John Humphrey
email: humphrjm@iu.edu

Elizabeth Nagel

James G Carlucci

Andrew Edmonds

Aarti Kinikar

Kim Anderson

Valériane Leroy

Daisy Machado

Dwight E Yin

Marco Tulio Luque

Esaú Custódio

João Filho

Madeleine Amorissani-Folquet

Safari Mbewe

Tulathip Suwanlerk

Athanase Munyaneza

Rena C Patel

Beverly Musick

Lisa Abuogi

Kara Wools-Kaloustian

Integration of HIV care into maternal and child health services in the global IeDEA consortium

Keywords: decentralization, pregnant women, postpartum, infant, service & deployment models, HIV service delivery, care model

come   L'archive ouverte pluridisciplinaire

Introduction

The World Health Organization (WHO) defines HIV integration as "the co-location and sharing of services and resources across different health areas and includes offering HIV testing, prevention, treatment and care services alongside other relevant health services" [START_REF]Consolidated guidelines on HIV prevention, testing, treatment, service delivery and monitoring: Recommendations for a public health approach[END_REF]. In 2006, the WHO recommended the integration of routine HIV services within maternal and child health (MCH) services as a strategy to reduce the fragmentation of and promote retention in care for pregnant and postpartum women living with HIV (WWH) and their infants [START_REF]World Health Organization. Technical consultation on the integration of HIV interventions into maternal, newborn and child health services[END_REF][START_REF]Integrated health services: what and why? Technical brief[END_REF]. Limited evidence from low-and middle-income countries (LMICs) suggests that integration improves outcomes for these populations, including uptake of maternal and infant HIV testing and antiretroviral treatment (ART), retention in care, and care quality [START_REF] Car | Integrating prevention of mother-to-child HIV transmission programs to improve uptake: a systematic review[END_REF][START_REF] Torpey | Increasing the uptake of prevention of mother-to-child transmission of HIV services in a resource-limited setting[END_REF][START_REF] Aliyu | Integrated prevention of mother-to-child HIV transmission services, antiretroviral therapy initiation, and maternal and infant retention in care in rural north-central Nigeria: a cluster-randomised controlled trial[END_REF][START_REF] Ezeanolue | Why are children still being infected with HIV? Impact of an integrated public health and clinical practice intervention on mother-to-child HIV transmission in Las Vegas, Nevada, 2007-2012[END_REF][START_REF] Killam | Antiretroviral therapy in antenatal care to increase treatment initiation in HIVinfected pregnant women: a stepped-wedge evaluation[END_REF][START_REF] Suthar | Integrating antiretroviral therapy into antenatal care and maternal and child health settings: a systematic review and meta-analysis[END_REF][START_REF] Berlacher | Integrating prevention of mother-to-child transmission of HIV care into general maternal child health care in western Kenya[END_REF]. Integration may also facilitate longitudinal HIV testing and early diagnosis for infants and children exposed to HIV (ICEH), which is particularly critical in settings such as sub-Saharan Africa where routine breastfeeding may last 24 months or more [START_REF] Breastfeeding | Late postnatal transmission of HIV-1 in breast-fed children: an individual patient data meta-analysis[END_REF]. Adverse effects of integration have also been reported, and include heavier provider workloads, increased patient wait times, insufficient clinic space and resources, the risk of unwanted HIV status disclosure, and the need to revise monitoring and evaluation tools and reporting systems for pregnant WWH and their infants and children exposed to HIV (ICEH) [START_REF] Winestone | Acceptability and feasibility of integration of HIV care services into antenatal clinics in rural Kenya: a qualitative provider interview study[END_REF][START_REF] Edmonds | Implementation and operational research: decentralization does not assure optimal delivery of PMTCT and HIV-exposed infant services in a low prevalence setting[END_REF][START_REF] Vo | Patient satisfaction with integrated HIV and antenatal care services in rural Kenya[END_REF][START_REF] Bulstra | Integrating HIV services and other health services: a systematic review and meta-analysis[END_REF][START_REF] Humphrey | Barriers and enhancers to retention in integrated HIV and maternal and child health care: the IeDEA-Kenya PMTCT cohort[END_REF]. Moreover, while some have advocated for integration as a strategy to enhance program efficiency, particularly in the context of declining donor funding for HIV, data supporting the cost-effectiveness of integration have been mixed, in part because per-patient cost savings associated with integration are offset by the resources needed for implementation [START_REF] Bulstra | Integrating HIV services and other health services: a systematic review and meta-analysis[END_REF]. Consequently, nearly two decades after the WHO first recommended the integration of HIV and MCH services, the WHO evidence grade for this recommendation remains very-low-certainty [START_REF]Consolidated guidelines on HIV prevention, testing, treatment, service delivery and monitoring: Recommendations for a public health approach[END_REF].

Despite this uncertainty, there is a growing body of literature indicating that integrated HIV and MCH services are increasingly being adopted in LMICs, particularly in sub-Saharan Africa where the burden of HIV is highest [START_REF] Bulstra | Integrating HIV services and other health services: a systematic review and meta-analysis[END_REF]. Yet while these studies suggest that HIV services are more commonly integrated with MCH services compared to other health services, the extent to which HIV care and treatment programs in LMICs have adopted HIV and MCH integration globally is unknown [START_REF] Car | Integrating prevention of mother-to-child HIV transmission programs to improve uptake: a systematic review[END_REF][START_REF] Suthar | Integrating antiretroviral therapy into antenatal care and maternal and child health settings: a systematic review and meta-analysis[END_REF][START_REF] Bulstra | Integrating HIV services and other health services: a systematic review and meta-analysis[END_REF]. The ways that HIV and MCH integration is configured within programs is also largely unknown and likely heterogeneous, and may include HIV testing, ART initiation for patients newly diagnosed with HIV, or continuation of ART for established patients. Understanding the current epidemiology and implementation of integrated HIV and MCH services is needed to guide research on the drivers and outcomes of HIV and MCH integration in LMICs.

The International epidemiology Databases to Evaluate AIDS (IeDEA) is a research consortium established by the U.S. National Institutes of Health which pools and harmonizes HIV data from over two million people with and at risk of HIV at clinical sites in 44 countries around the world (www.iedea.org). IeDEA has conducted periodic consortium-wide site assessment surveys describing the available resources and implementation of HIV care and treatment for people living with HIV at affiliated sites since 2009 [START_REF] Duda | Characteristics and comprehensiveness of adult HIV care and treatment programmes in Asia-pacific, sub-saharan Africa and the americas: results of a site assessment conducted by the international epidemiologic databases to evaluate AIDS (IeDEA) collaboration[END_REF][START_REF] Fritz | Comprehensiveness of HIV care provided at global HIV treatment sites in the IeDEA consortium: 2009 and 2014[END_REF]. Data from these surveys are used to document sitelevel capacity and availability of services critical to understanding global trends in HIV care and treatment implementation, as such data are not usually available in routine program databases. IeDEA's latest site assessment was implemented in 2020-2021, offering a unique opportunity to assess the uptake of integrated HIV and MCH services within LMICs globally. The objective of this study was to determine the prevalence and characteristics of integrated HIV and MCH services at LMIC sites participating in the global IeDEA consortium.

Methods

Setting and study population

The IeDEA site assessment was a cross-sectional survey of all clinical sites that contributed longitudinal patient data to IeDEA in 2020. These sites represent seven geographic regions: Asia-Pacific, the Caribbean, Central and South America Network for HIV Epidemiology (CCASAnet), North America (i.e., The North American AIDS Cohort Collaboration on Research and Design, NA-ACCORD), and four sub-Saharan Africa regions (Central, East, Southern, and West Africa). As the Southern Africa region included >200 small clinics contributing data to IeDEA as part of larger programmatic cohorts, it was not considered feasible to survey 100% of active sites in this region. Therefore, a systematic, hybrid sampling strategy was used to (i) purposefully sample sites that had completed prior IeDEA site surveys to facilitate future longitudinal analyses, and (ii) ensure that selected sites were representative of the larger programmatic cohort by randomly sampling sites stratified by location (urban vs. rural) in line with the clinic distribution within each programmatic cohort. Thus, 32 representative sites from the Southern Africa region (15% of active sites) were included in the site assessment, which included sites that were purposively sampled (n = 5), randomly sampled (n = 18), and those in IeDEA's database that are not part of a large programmatic cohort (n = 9) [START_REF] Brazier | Design and implementation of a global site assessment survey among HIV clinics participating in the International epidemiology Databases to Evaluate AIDS (IeDEA) research consortium[END_REF].

Sites in IeDEA regions were eligible for this analysis if they reported providing HIV services to pregnant WWH, postpartum WWH, or ICEH <24 months of age. NA-ACCORD was not included in the analysis as it comprises high-income countries with low HIV burdens, where factors influencing the integration of HIV and MCH services may differ markedly from those in LMICs. Sites and coordinating centers for all regions had institutional review board approvals in place permitting the collection of site-level data for this survey. Specifically, this study was approved by the Vanderbilt University Institutional Review Board where the survey data are housed.

Data collection and management

Survey development and data collection methods have been previously described [START_REF] Fritz | Comprehensiveness of HIV care provided at global HIV treatment sites in the IeDEA consortium: 2009 and 2014[END_REF]. Briefly, IeDEA investigators developed the survey based on prior IeDEA-wide surveys and input from technical working groups. Core domains of the survey that pertained to this study included patient populations served, HIV testing, and HIV care and treatment. Questions about the integration of HIV and MCH services were also incorporated into the survey and included the locations of HIV care and ART initiation for pregnant WWH, postpartum WWH, and ICEH. These location response options were not mutually exclusive, such that respondents were allowed to indicate more than one location of HIV care and ART initiation for each population at their clinic. Though originally intended to assess service delivery at the time the survey was administered in 2020-2021, the year 2019 was selected as the reference period for all survey questions due to the potential for disruptions in service delivery related to the COVID-19 pandemic. The survey was programmed in REDCap and distributed using a web-based link to a designated clinical staff member for each IeDEA clinic or cohort of clinics. Some sites completed paper-based surveys, which were entered into REDCap. The accuracy of data input was verified by the regional data team. REDCap servers were housed in a local data center hosted at Vanderbilt University Medical Center. Data from English and French surveys were merged in REDCap and exported for analysis.

To inform our interpretation of the data, we also conducted a non-systematic search of the literature (PubMed, Google scholar) and ministry of health websites for policies recommending the integration of HIV and MCH services on or before 2019 in each country included in the IeDEA survey. For this search, the presence of integration policy was defined as any statement recommending the delivery of HIV care or ART initiation in MCH clinic from a ministry of health or other government entity. The search was facilitated and verified by the study coauthors representing each IeDEA region. Countries for which integration policy was not identified in our search were designated as having "unconfirmed" integration policy to acknowledge the potential limitations of our non-systematic search. The results of the search were descriptively summarized and presented in the Supplementary Material (Supplementary Table S1).

Statistical analysis

Site characteristics relevant to service delivery for MCH clients were descriptively summarized overall, by IeDEA region, and by population setting (urban, rural, or mixed urban/rural). The primary outcome was the proportion of sites providing HIV services integrated within MCH clinics for pregnant WWH, postpartum WWH, and ICEH, respectively. For pregnant WWH, this included integration of HIV services within antenatal care (ANC) clinics; for postpartum WWH, this included integration of HIV services within postnatal care (PNC) clinics (i.e., clinics for postpartum women only) or MCH clinics (i.e., clinics for women and infants); and, for ICEH, this included integration of HIV services within well-baby clinics (i.e., clinics for infants) or MCH clinics. Integration was defined as full (integration of HIV care and ART initiation), partial (integration of HIV care or ART initiation), and no integration. These definitions were based on WHO guidance [START_REF]Consolidated guidelines on HIV prevention, testing, treatment, service delivery and monitoring: Recommendations for a public health approach[END_REF][START_REF]HIV Care and support: hIV care and support taking into account the 2016 WHO consolidated guidelines[END_REF]. Tableau (Tableau Software, LLC, Seattle, WA) was used to map the IeDEA sites included in the analysis, and SAS version 9.4 (SAS Institute Inc., Cary, NC) was used for analysis.

Results

Between September 2020 and March 2021, clinical staff at 202 sites in 40 LMICs completed the survey, and of these sites, 193 (96%) reported providing services to pregnant WWH, postpartum WWH, or ICEH and were included in the analysis (Figure 1). The number of sites included in the analysis in each IeDEA region were: Asia-Pacific (n = 48), CCASAnet (n = 8), Central Africa (n = 21), East Africa (n = 74), Southern Africa (n = 28) and West Africa (n = 14).

Overall, 58 (30%) sites served an urban population, 43 (22%) served a rural population, and the remainder served a mixed urban/rural population (Table 1). Most sites reported providing services to pregnant WWH (92%), postpartum WWH (88%), or ICEH (82%), while fewer sites (73%) provided services to all three groups. Pregnancy/breastfeeding services and ICEH services were available every day, as opposed to special/dedicated days, in 60% and 74% of sites, respectively. HIV DNA or RNA PCR for infant HIV diagnosis testing was available at 81% of sites, ranging from >85% in East, Southern and West Africa to 54%-75% in the other regions.

For pregnant WWH, HIV care was most frequently delivered in the ANC clinic in 80% of sites in East and Southern Africa (Table 2). However, 84% of sites in Southern Africa also reported delivering HIV care to pregnant WWH in the HIV clinic, compared to 19% of sites in East Africa. As with Southern Africa, other regions had similar proportions of sites providing HIV care to pregnant WWH in HIV and ANC clinics. Among all sites, ART initiation for pregnant WWH was less frequently offered in ANC clinics (59%) compared to HIV clinics (71%). Full and partial integration of services for pregnant WWH occurred in 54% and 21% of sites, respectively, with the highest proportions of fully integrated sites reported in Southern Africa (80%) and East Africa (76%).

For postpartum WWH, HIV care was delivered in the MCH clinic in 51% of sites overall and was highest in East Africa (76%). In contrast, approximately 80% of sites in the Asia-Pacific, CCASAnet, and Central and West Africa delivered HIV care in the HIV clinic. In Southern Africa, the location of HIV care for postpartum WWH was approximately 50% in each of the HIV, PNC, and MCH clinics. The locations of ART initiation for postpartum WWH (i.e., at the HIV, well-baby, MCH or other clinic) generally mirrored the locations of HIV care for postpartum WWH in each region. Full and partial integration of services for postpartum WWH occurred in 51% and 9% of sites, respectively, with the highest proportions of fully integrated sites in East Africa (76%) and Southern Africa (64%).

For ICEH, HIV care was delivered in the MCH clinic at 55% of sites overall and was highest in East Africa (78%) followed by Southern Africa (63%). Compared to the MCH clinic, the well-baby clinic accounted for a higher proportion of HIV care Stratifying the integration outcome by population setting, full integration for pregnant WWH (74%), postpartum WWH (78%), and ICEH (80%) was more prevalent in rural settings compared IeDEA sites included in the analysis. with HIV, including two-thirds of all children with HIV [START_REF]Joint United Nations Programme on HIV/AIDS (UNAIDS)[END_REF]. It is possible that the high levels of integration in these regions, compared to other regions in our study, are the result of policies and research responsive to their higher burdens of HIV among women and their exposed children, and the need to enhance access to HIV care and treatment services by integrating HIV and MCH services for these populations [START_REF]Consolidated guidelines on HIV prevention, testing, treatment, service delivery and monitoring: Recommendations for a public health approach[END_REF][START_REF] Bulstra | Integrating HIV services and other health services: a systematic review and meta-analysis[END_REF]. In Kenya, for example, significant investments in integration research and stakeholder engagement likely played a critical role in promoting integration in Kenya and more broadly in the region [START_REF] Turan | Implementation and operational research: effects of antenatal care and HIV treatment integration on elements of the PMTCT cascade: results from the SHAIP cluster-randomized controlled trial in Kenya[END_REF][START_REF] Washington | Implementation and operational research: effect of integration of HIV care and treatment into antenatal care clinics on mother-to-child HIV transmission and maternal outcomes in nyanza, Kenya: results from the SHAIP cluster randomized controlled trial[END_REF][START_REF] Turan | The study of HIV and antenatal care integration in pregnancy in Kenya: design, methods, and baseline results of a cluster-randomized controlled trial[END_REF][START_REF] Reynolds | Reflections on the Integration for Impact Conference: The MEASURE Evaluation blog[END_REF]. Not all sites in East and Southern Africa offered integrated services, however, and there was heterogeneity in the prevalence and characteristics of integration both within and between IeDEA regions in our study. Similar heterogeneity in the uptake of integration was identified in a systematic review conducted in 2010 (4). We also could not identify policies recommending HIV and MCH integration in more than half of countries in CCASAnet and Central Africa. Although, it is possible that those countries lacking an explicit integration policy in Ministry of Health guidance were reliant on WHO or regional guidelines (e.g., Pan American Health Organization) for such policy [START_REF]Consolidated guidelines on HIV prevention, testing, treatment, service delivery and monitoring: Recommendations for a public health approach[END_REF][START_REF]Regional initiative for the elimination of mother-to-child transmission of HIV and congenital syphilis in Latin America and the Caribbean: regional monitoring strategy[END_REF]. More research is needed to determine the factors driving integration in LMICs, and the impact of integration on HIV vertical transmission and other maternal and child health outcomes, to understand this heterogeneity and how to measure and address it through WHO and national policy implementation [START_REF] Abuogi | Achieving UNAIDS 90-90-90 targets for pregnant and postpartum women in sub-Saharan Africa: progress, gaps and research needs[END_REF].

Several factors could explain the lower proportions of integrated HIV and MCH services outside of East and Southern Africa. In the Asia-Pacific, the lower levels of HIV and MCH integration may relate to this region's higher overall economic status compared to other regions. The IeDEA Asia-Pacific region includes countries from upper-middle (China, Malaysia, Taiwan, Thailand) and high (Austrailia, Japan, South Korea) income strata according to World Bank classifications [START_REF]World bank country and lending groups[END_REF]. These countries may have sufficient resources and infrastructure to meet the individual HIV care and treatment needs of WWH and their infants within existing care systems. The lower levels of HIV and MCH integration in the Asia-Pacific could also relate to the nature of this region's epidemic which is largely driven by key populations such as men who have sex with men, sex workers, and people who inject drugs, as opposed to the epidemic in sub-Saharan Africa which disproportionately affects heterosexual women of childbearing potential [START_REF]Joint United Nations Programme on HIV/AIDS (UNAIDS)[END_REF]. Therefore, it may be the case that policy implementation and resources in the Asia-Pacific region are primarily focused on these key populations. Nevertheless, some countries, such as the Philippines, are experiencing a resurgence in HIV incidence among women [START_REF]Joint United Nations Programme on HIV/AIDS (UNAIDS)[END_REF]. Some countries are also experiencing challenges transitioning from a reliance on international aid to domestic financing of HIV services, particularly in the context of the COVID-19 pandemic. These challenges underscore the need to better understand the advantages of integration in different settings and the impact of country-level policies on integration implementation.

It is also possible that integration is linked in part to a site's geographic setting. In our study, integration was most prevalent at sites serving rural and mixed urban/rural populations compared to urban populations for pregnant and postpartum WWH, and ICEH. Rural clinics may have been better positioned and incentivized to implement integrated HIV and MCH services given more available clinic space or the need to optimize staffing and resource allocation. Patients desiring access to more specialized services and advanced care at urban clinics may also act as a counter force to integration in these settings, compared to rural clinics with less access to these services. Furthermore, the potential association between integration and rural settings was mostly driven by East Africa, which accounted for 37 of 43 (86%) rural sites included in the analysis, whereas sites in other IeDEA regions had relatively higher proportions of urban and mixed urban/rural population settings. The international and national integration policies we reviewed do not distinguish between rural and urban settings. These findings highlight the significant need for further research to understand what is enabling MCH integration in rural areas which may be transportable to other settings.

A strength of our study is its use of the well-established IeDEA-wide site assessment platform to survey global HIV care and treatment sites. This platform enabled us to gather unique global data that have not been previously reported. A potential limitation of our study is that the IeDEA sites included in the analysis may not be generalizable to the broader array of HIV care and treatment sites in the countries represented. For example, sites were initially selected to participate in IeDEA based on their data collection infrastructures, which may imply that they have higher levels of resources, funding and available services compared to non-IeDEA sites. This potential limitation is the reason we elected not to segment the data at the country level. Our data may also be subject to social desirability and reporting biases by clinical staff who completed the surveys, as well as biases arising from the ways the questions were interpreted, for which there was limited ability for investigators to verify responses. Recall bias is also a potential limitation, as respondents were asked to consider practices prior to, rather than during, the COVID-19 pandemic.

Our non-systematic search may have failed to identify relevant ministry of health integration policies for some countries. Countrylevel guidance on MCH integration can be disseminated through local policy circulars, notices and press releases published years ago that are no longer searchable electronically, so we did not consider it feasible to systematically assess all potentially related policy documents for all countries. Rather, our search was enhanced by direct communications with IeDEA regional and country-level representatives who were able to provide expertise on integration policy for each country. Donor policies and priorities, such as the U.S. President's Emergency Plan for AIDS Relief (PEPFAR), may also have important influences on integration which were not accounted for in our search [START_REF] Duda | Characteristics and comprehensiveness of adult HIV care and treatment programmes in Asia-pacific, sub-saharan Africa and the americas: results of a site assessment conducted by the international epidemiologic databases to evaluate AIDS (IeDEA) collaboration[END_REF]. Still, the findings from our search align with a recent systematic review assessing global HIV and MCH integration research, as well as WHO guidance recommending integration of HIV and other health services particularly in areas with high HIV prevalence [START_REF]Consolidated guidelines on HIV prevention, testing, treatment, service delivery and monitoring: Recommendations for a public health approach[END_REF][START_REF] Bulstra | Integrating HIV services and other health services: a systematic review and meta-analysis[END_REF]. Finally, the structured site survey did not allow us to fully tease apart the nuances of service delivery at each site, for example, in Southern Africa, where high proportions of sites reported providing HIV care to pregnant WWH in both the MCH and HIV clinic. In future research involving these sites, we will seek to better understand the factors influencing integration as well as the various nuances of service delivery, including measures of service quality and associations with clinical outcomes for pregnant and postpartum WWH and ICEH.

Conclusion

The integration of HIV and MCH services was most prevalent in East and Southern Africa, regions with the highest burdens of HIV disease and prevalence among women globally. However, there was heterogeneity in the prevalence of integration both within and between regions. More research is needed to understand the factors driving integration of HIV and MCH services, and the impacts of integration on vertical transmission and other maternal and infant outcomes, to inform how best to address the gaps in integration implementation. The findings of our study will be useful to policymakers interested in the impact of integration policy and its global implementation, as well as program stakeholders and researchers concerned with health system structures and improving service delivery to pregnant and postpartum WWH and their infants.

TABLE 1

 1 Characteristics of service delivery for pregnant and postpartum women with HIV and infants with perinatal HIV exposure, by IeDEA region, September 2020 to March 2021.

FIGURE 1

 1 FIGURE 1

FIGURE 2

 2 FIGURE 2Integration of HIV and maternal and child health services, by urban and rural population setting, September 2020 to March 2021.

Frontiers in Global Women's Health

frontiersin.org

Funding

The International Epidemiology Databases to Evaluate AIDS (IeDEA) is supported by the U.S. National Institutes of Health's

to 30%-53% of urban and mixed urban/rural settings (Figure 2; see Supplementary Table S1).

We found policies recommending integration for 31 of 40 (78%) countries, including at least one country in each IeDEA region (Supplementary Table S2). The proportions of countries with integration policy, by region, were: Asia Pacific (12/12, 100%), CCASAnet (2/7, 29%), Central Africa (2/5, 40%), East Africa (3/3, 100%), Southern Africa (6/6, 100%), and West Africa (6/7, 86%).

Discussion

Integration of HIV and MCH services was reported in all IeDEA regions, with East and Southern Africa reporting the highest proportions of fully integrated services. In addition, we identified country-level policies recommending HIV and MCH integration for all countries in the East and Southern Africa IeDEA regions. East and Southern Africa have the highest burdens of HIV in the world, and account for half of all people 16) 2 ( 20) 44 ( 25)

Data availability statement

Complete data for this study cannot be posted in a supplemental file or a public repository because of legal and ethical restrictions. The Principles of Collaboration under which the IeDEA multiregional collaboration was founded and the regulatory requirements of the different countries' IRBs require the submission of a project concept proposal and approval by the IeDEA Executive Committee. To request data, please review IeDEA guidance and complete the concept proposal template, available at: https://www.iedea.org/resources/multiregionalresearch-sops-templates/. Signing of a data sharing agreement may also be required. Requests to access the datasets should be directed to humphrjm@iu.edu.

Ethics statement

The studies involving human participants were reviewed and approved by Vanderbilt University Institutional Review Board. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.

Author contributions

JH, LA, KW: conceptualized the study. AE, AK, KA, VL, DM, MTL, MA, SM, TS, and AM: contributed to data acquisition. BM: analyzed the data. JH prepared the original draft with contributions from BN. All authors contributed to the drafting and critical revision of the manuscript and read and approved the final manuscript. All authors contributed to the article and approved the submitted version.

Library of Medicine: Asia-Pacific, U01AI069907; CCASAnet, U01AI069923; Central Africa, U01AI096299; East Africa, U01AI069911; NA-ACCORD, U01AI069918; Southern Africa, U01AI069924; West Africa, U01AI069919. Informatics resources are supported by the Harmonist project, R24AI24872. This work is solely the responsibility of the authors and does not necessarily represent the official views of any of the institutions mentioned above.

Conflict of interest

KA has received funding from ViiV Healthcare which is unrelated to this project. All other authors declare that they have no competing interests.

Publisher's note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fgwh.2023. 1066297/full#supplementary-material.


Pavel Caha

Karen De Clercq

Guido Vanden Wyngaerd

The split-comparative hypothesis and the morphology of comparative adverbs in Czech

Keywords: adjectives, adverbs, allomorphy, comparative, morphology, nanosyntax

, according to which the comparative head splits into two independent projections, C1 and C2. The second idea is a split ADV hypothesis (hinted at in Bobaljik 2012), according to which there are two positions for an ADV head in the functional sequence.

Introduction

This article explores the morphosyntactic relationship between comparative adjectives and comparative adverbs in Standard Czech and two Moravian 1 dialects (East and Central). The forms under investigation exhibit complex patterns of allomorphy, where the shape of the comparative marker is influenced by two factors. The first factor concerns the (arbitrary) class of the root: the comparative degree is expressed differently for different roots. The second factor is part of speech (adjective or adverb). Czech has a productive way of forming adverbs related to adjectives, including comparative adverbs. The morphology of degree marking is affected by the distinction between an adjective and an adverb in a number of rather complex ways.

We argue that in order to capture these patterns, we need to adopt two proposals. The first one is the Split-Comparative Hypothesis [START_REF] Caha | The fine structure of the comparative[END_REF]. The hypothesis says that the comparative meaning is not atomic, and it should be decomposed into two components of meaning as in (1), where we call the components C1 and C2.

(1)

The Split Comparative Hypothesis:

comparative = [[[positive] C1 ] C2]
The hypothesis in (1) follows the standard idea that the comparative is derived from the positive (see, e.g., [START_REF] Bobaljik | Universals in comparative morphology[END_REF][START_REF] Grano | Universal markedness in gradable adjectives revisited. The morpho-semantics of the positive form in Arabic[END_REF]. The new thing about it is that the comparative is not added as a single meaning component, but it is derived by adding two components of meaning.

The second ingredient we need is a proposal for adverbs. In [START_REF] Bobaljik | Universals in comparative morphology[END_REF] seminal work, it has been proposed that comparative adverbs can be formed in two different ways. In some languages, comparative adverbs are derived from positive-degree adverbs, as in (2a). We call the relevant adverbial head LOADV, since it comes below the comparative. In other languages, comparative adverbs are derived from comparative adjectives (by turning a comparative adjective into an adverb), as in (2b). We call the adverbial head HIADV, since it is found above the comparative.

(2)

Two ways of forming a comparative adverb [START_REF] Bobaljik | Universals in comparative morphology[END_REF] a.

[[[ A ] LOADV ] CMPR ] b. [[[ A ] CMPR ] HIADV]

The current paper proposes that the complex patterns of allomorphy in Czech can be explained under the idea that it has both the low and the high ADV head. We call this the split adverb hypothesis. We depict the idea in a simplified form in (3), noting that in the final version of our proposal, the CMPR head will have to be split into C1 and C2.

(3)

Our proposal (simplified version) [[[[ A ] LOADV ] CMPR ] HIADV ]

The paper is organised as follows. Section 2 discusses the formation of comparative adjectives in Czech, focussing on the fact that the shape of the comparative marker is influenced by the root. Section 2 also presents the account by [START_REF] Caha | The fine structure of the comparative[END_REF], which has been designed to explain how exactly the root determines the form of the suffix. In Section 3, we turn to the fact that the comparative marker is not only influenced by the root, but also by the adjective/adverb distinction. These patterns are rather complex and, as we argue, impossible to derive under the idea that Czech only has a single adverbial head. In Section 4, we show how these facts can be explained under the hypothesis that Czech has both a low and a high adverbial head. Section 5 discusses adverbs in the dialects. Section 6 concludes.

Comparative adjectives

In this section, we discuss comparative adjectives in Standard Czech. In doing so, we also provide the account of the allomorphic variation proposed in [START_REF] Caha | The fine structure of the comparative[END_REF].

The first thing to know is that Standard Czech comparatives are formed by two allomorphs, namely ějš or š. The allomorph ějš is illustrated in (4a), š is in (4b The two adjectives in (4) are similar both in their phonology and their meaning. This indicates that the use of one or the other marker is not uniquely determined by the phonology or the meaning of the base. The decision which roots require š and which ějš is therefore an idiosyncratic property of the root.2

We illustrate the 'arbitrary' nature of allomorph selection in more detail in table (5). In this table, we put side by side adjectival roots that have similar phonology, yet they differ in their comparative allomorphs. In the table, the root on the left (e.g. star-'old' on the first row) always has similar phonology as the root on the right (e.g. čir-'pure'), but the allomorphs differ (see Vyshnevska 2022 for similar observations concerning Ukrainian).

(5

) POS CMPR GLOSS POS CMPR GLOSS a. star-ý star-š-í 'old' čir-ý čiř-ejš-í 'pure' b. bohat-ý bohat-š-í 'rich' svat-ý svat-ějš-í 'saint' c. tvrd-ý tvrd-š-í 'hard' hrd-ý hrd-ějš-í 'proud' d. drah-ý draž-š-í 'expensive' uboh-ý ubož-ejš-í 'poor'
It can be observed that each of the suffixes triggers particular consonant mutations at the end of the base. The comparative marker š palatalises velars (see (5d)). The suffix ějš palatalizes velars, dentals, alveolars and labials. Palatalisation of the preceding consonant is sometimes marked directly on the consonant (e.g. ř in (5a) and ž in (5d)). Other times, it is marked on the vowel (as ě), yet the effect is the same. For instance, the comparative svat-ěj-š-í on line (5b) contains a palatalised root (IPA: svacEjSi:).

Let us now turn to the form of the two allomorphs, ějš and š. It has been argued in the literature [START_REF] Caha | Suppletion and morpheme order: Are words special[END_REF][START_REF] Caha | The fine structure of the comparative[END_REF]) that the comparative marker ějš should be decomposed into two independent morphemes, namely ěj and š. The first reason is that this explains the (phonological) containment of š inside ějš, since after the decomposition, ěj-š actually contains š as a subpart. The second reason is that each of the two morphemes can surface independently. We already saw this in ( 5), where -š can appear without -ěj. Conversely, comparative adverbs in Standard Czech lack š, and only contain ěj, as shown in ( 6).

(6) Adverbs in Standard Czech CMPR ADJ CMPR ADV GLOSS chab-ěj-š-í chab-ěj-i 'weak' rychl-ej-š-í rychl-ej-i 'fast' červen-ěj-š-í červen-ěj-i 'red' hloup-ěj-š-í hloup-ěj-i 'stupid'
These fact support the idea that -ěj and š are independent morphemes. [START_REF] Caha | The fine structure of the comparative[END_REF] propose that the morphological complexity of the comparative marking indicates that the comparative meaning is also complex, and requires the addition of at least two semantic ingredients. [START_REF] Caha | The fine structure of the comparative[END_REF] call these C1 and C2, proposing that each of these meaning components heads an independent projection, as in (7). The morphemes ěj and š are the realization of these meanings. As [START_REF] Caha | The fine structure of the comparative[END_REF] point out, the proposal in (10) is compatible with the fact that the positive degree is realised by the same root slab 'weak,' as in (11). This is because of the fact that in the Nanosyntax approach, insertion is driven by the Superset Principle:

(12)
The Superset Principle [START_REF] Starke | Nanosyntax: A short primer to a new approach to language[END_REF]) A lexically stored tree matches a syntactic node iff the lexically stored tree contains the syntactic node.

To see how this principle works, consider the lexical entry of the adjective slab-'weak' in (13), which connects a phonology (on the left) with a syntactic tree (middle), and a concept (on the right):

( The take-home message is that [START_REF] Caha | The fine structure of the comparative[END_REF] use root size to model the type of allomorph that each root combines with. This leads to a simplification of the rules of exponence that describe the realisation of the c1 head (ěj or zero). Moreover, the approach provides a way to deal with root suppletion in an elegant way, since C1P sized roots lexicalise different features in the positive and in the comparative. The analysis of suppletion correctly predicts that all suppletive adjectives will be in the š-í class [START_REF] Caha | The fine structure of the comparative[END_REF]. With this background, let us now turn to the discussion of comparative adverbs.

Comparative adverbs in Standard Czech

This section shows how adverb formation influences the marking of the comparative. Table (18) (repeated from (6) above, but with the positive forms added, for reasons to be made clear below) gives the standard forms of comparative adverbs corresponding to ěj-š-í adjectives.

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Adverbs of ěj-š-í adjectives Standard Czech, positive included

CMPR ADJ CMPR ADV GLOSS POS ADJ POS ADV chab-ěj-š-í chab-ěj-i 'weak' chab-ý chab-ě rychl-ej-š-í rychl-ej-i 'fast' rychl-ý rychl-e hloup-ěj-š-í hloup-ěj-i 'stupid' hloup-ý hloup-ě
The table illustrates the fact that all the ěj-š-í adjectives form adverbs in ěji. [START_REF] Caha | The fine structure of the comparative[END_REF] propose an account where the structure of the adverb has both C1 and C2 (despite the absence of š). In addition, there is an ADV head above C2, see ( 19).

(

) ADVP C2P C1P AP ... C1 ěj C2 ADV chab 'weak' -i (20) ADVP C2P C1P AP ... C1 C2 ADV slab 'weak' -i 19
The reason why š is not present in (19) (despite the presence of C2) is because it is blocked by the adverbial ending i, which is a portmanteau that spells out the C2 projection along with the high ADV head. This is indicated by the brace in (20). 5 The idea that the ending i is a portmanteau for C2 and ADV is supported by the fact that adverbs in the positive never have i; they have the adverbial ending ě instead. This ending is different because it does not lexicalise C2. This can be seen in Table ( 18) on the right.

The theory proposed in [START_REF] Caha | The fine structure of the comparative[END_REF] thus successfully deals with adverbs corresponding to ěj-š-í adjectival comparatives, using a structure with a high Adv head. However, the account faces difficulties with the š-í class of comparatives, where it wrongly predicts adverbs like *slab-i 'weak'. To see why this is the case, consider (20). The root of š-í adjectives will realise AP+C1 (recall the adjectival comparative in ( 10)). This leaves C2+ADV, which will be realised as -í, precisely as in ( 19), yielding forms like *slab-í 'weak'. The comparative adverbs we do get in the adjectives with š-í are of two types, with the type depending on the root. The first (most common) type of adverb is shown in Table (21). The adverb is morphologically identical to the adverbs formed from ěj-š-í comparatives.

CMPR ADJ CMPR ADV GLOSS POS ADJ POS ADV slab -š-í slab-ěj-i 'weak' slab-ý slab-ě tuž -š-í tuž-ej-i 'tough' tuh-ý tuz-e tvrd -š-í tvrd-ěj-i 'hard' tvrd-ý tvrd-ě
The fact that ěj appears in the adverbs corresponding to š-í adjectives is mysterious. In the system proposed by [START_REF] Caha | The fine structure of the comparative[END_REF], it is expected that whenever a particular head can be spelled out by the root, then this type of realisation must be preferred to other ways of realizing it.6 This is ultimately the reason why comparative adjectives like slab-š-í 'weaker' lack ěj: since the root can spell out C1, ěj is not needed. Therefore, the class of adverbs in ( 21) is problematic because ěj surfaces in the adverb with roots that can lexicalise C1. The marker ěj in fact shows a complex distribution, being sensitive both inwards (to the identity of the root), and outwards (to the final morpheme of the comparative). It is sensitive to the root, because it does not appear in the context of a selected class of roots. However, this is so only when the form is used as an adjective, but not when an ADV head is introduced higher up, in which case ěj must appear again. We shall show below how the postulation of a second, low ADV head explains this complex distribution.

The second class of comparative adverbs corresponding to š-í comparatives is shown in Table (22). This is a minor class, populated mainly by suppletive adjectival comparatives.

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Standard Czech comparative adverbs (š-í adjectives, Class II)

CMPR ADJ CMPR ADV GLOSS POS ADJ POS ADV draž -š-í dráž -e 'expensive' drah-ý draz-e lep -š-í lép -e 'good' dobr-ý dobř-e del -š-í dél -e 'long' dlouh-ý dlouz-e
These adverbs come close to the predicted form, because they lack ěj just like the corresponding adjectives. With these roots, it appears that C1 is spelled out by the root both in the adjective and in the adverb. However, the adverbs also show two unexpected features. First of all, the adverbial marker is not the predicted i, but e. This may initially look like the adverbial marker that we find in the positive degree, given in the final column in ( 22). However, we assume that these are different morphemes, since they interact differently with the final consonant of the root. This can be seen with the root drah 'expensive,' where we get draz in the positive and dráž in the comparative. It is known that in the Czech phonology, different endings trigger different palatalisations of the base, and since the palatalisations are different here, these are quite likely to be different e's.

Another noteworthy fact is that the root always lengthens in the comparative adverb in ( 22), e.g., the adjectival root drah 'expensive' is realised as dráž in the adverb (the accent on the vowel indicates length). Such lengthening looks as something specific to this class of comparative adverbs, and we shall capture it by proposing that the adverbial marker e is accompanied by an empty vocalic space µ, that triggers the lengthening of the root.

To summarise, [START_REF] Caha | The fine structure of the comparative[END_REF] posited two classes of roots, yielding two different types of comparative adjectives: š-í vs. ěj-š-í. When comparative adverbs are introduced, it turns out that there are three classes of roots. This is because the š-í class of adjectives splits into two subclasses, where each subclass has a different way of forming the adverb, as we show in Figure 1, where the three arrows correspond to the three classes of adjectives. The notation PAL+µ+e represents the fact that comparative adverb suffix e triggers palatalisation (PAL) and lengthens the preceding vowel (µ).

Deriving the Standard pattern

In this section, we propose an account that delivers the correct pairing between the adjectival and the adverbial forms. The crucial idea is that adverbs have two additional heads compared to adjectives. Specifically, we propose a low adverb head (LOADV) in between C1 and C2, and a high adverbial head (HIADV) above C2:

(24) HIADVP HIADV C2P C2 LOADVP LOADV C1P C1 AP ...
This structure provides enough analytical space to propose more than two sizes of roots, which is empirically required. However, Bobaljik (2012: §4.2) also provides some independent cross-linguistic evidence for two different positions of an adverbial head in a comparative, which we review briefly below.

Evidence for the existence of a high adverb is based on morpheme ordering in Karelian. Consider the root 'quick' in (25). The comparative marker mpa (and its allomorphs) appears closer to the root than the adverbial marker h (in bold). This suggests that the adverbial endings sit in a structurally position higher than the comparative mpa.

(25)

Karelian 'quick' and 'good' (Bobaljik 2012: 118)

'quick' 'good' POS CMPR POS CMPR ADJ rutto rutto-mpa hyvä pare-mpi ADV rutto-h rutto-mpa-h hyv-in pare-mm-in
There are reasons to think that mpa spells out C2, and therefore, that h occupies the high adverb head of ( 24). The analysis of mpa as C2 is suggested by the patterning of suppletive adjectives in Karelian. Consider the forms of the suppletive adjective 'good' in (25). This adjective has the root hyvä 'good' for both positive forms and the root pare for the comparative forms. 7 Recall now from (17) that [START_REF] Caha | The fine structure of the comparative[END_REF] posit slightly different feature specifications for suppletive roots. Following this approach, the suppletive comparative root pare 'bett' would be specified as lexicalising AP+C1 (to make it different from the positive hyvä 'good,' which spells out just AP). However, specifying pare as C1 necessarily leads to the analysis of mpi as C2, because it comes on top of the suppletive root pare 'bett'. If this is so, the Karelian adverb marker must be hosted by an ADV head that is higher than both C1 and C2, and corresponds therefore to the high adverb head HIADV. Basque, on the other hand, leads to different conclusions concerning the location of the ADV head. Consider the forms of the root 'new' in (26). We see that the adverbial morpheme ki is closer to the root than the comparative ago.

(26)

Basque 'new' and 'good' [START_REF] Bobaljik | Universals in comparative morphology[END_REF] In sum, the patterning of the suppletive adjective 'good' in (27) tells us that ago is C2, and therefore, that the adverbial ki must be lower than C2. However, we do not know the position of ki relative to C1. With this question in mind, let us now turn to the adverbial forms of the adjective 'good' in (27).

The relevant fact in ( 27) is that in the comparative adverb, the adverbial ki attaches on top of the suppletive form hobe; the form *on-gi-ago (with gi attaching to the positive AP root) is ungrammatical. This indicates that even though ki is lower than C2 (because it is lower than ago), it must be higher than C1, else it would not combine with hobe. These considerations locate ki unequivocally between C1 and C2.

In sum, the two languages discussed here each provide a piece of evidence for a particular location of an ADV head, yet the location is different in each case. [START_REF] Bobaljik | Universals in comparative morphology[END_REF] concludes from this that the position of the ADV head is not fixed. In what follows, we show that if we assume for Czech the simultaneous presence of both of these heads, we are able to correctly model the pairing between adjectival and adverbial allomorphs of the comparative. 8With this much in place, we now return to the Czech patterns in Table (28 The structure of the comparative adverb is provided in (30), in which two things are worth noting. First, ěj spells out the LOADV head along with C1, as indicated by the brace. This is compatible with ěj lexicalising just C1 in the adjectival structure, since C1P is a subconstituent of [ LOADVP LOADV [ C1P C1]] (not shown in the trees, but created through leftward movement of AP in (24); see note 5). Second, the combination of C2+HIADV is realised as i. The other comparative adverb marker ě lexicalises just HIADV (as we shall show below). This means that the heads C2 and HIADV could in principle be lexicalised analytically as š-ě. However, the Nanosyntax spellout algorithm prefers portmanteau lexicalisation of the two heads by a single morpheme, so i is chosen in (30).

Let us next turn to the š-í → ěj-i class (second row in ( 28)). This is the class where [START_REF] Caha | The fine structure of the comparative[END_REF] wrongly predicted adverbs like *slab-i 'weaker'. Roots of this class are of size C1P. There is no need for ěj in the adjective, since the root spells out C1 (see ( 31)). However, in the comparative adverb in (32), ěj is the only marker that can spell out LOADV. The marker i then appears as the lexicalisation of C2+HIADV, exactly as in (30). This is then how the problematic class š-í → ěj-i arises: due to the additional LOADV head, ěj is needed in the adverb, even though it is missing in the adjective. 9The third and final Standard Czech class is š-í → ě. It can be captured by associating the root to the adverbial C2P indicated in (34). Such lexical item gives rise to an adverb where the root pronounces all the features except HIADV, which is realised as ě. In the comparative adjective in (33), the root cannot spell out C2P, since the C2P of ( 33) is not a sub-constituent of the root's lexical entry, which has the C2P tree as in (34). This is because the C2P of (33) lacks LOADV. As a result, the root only spells out C1P, and C2 is spelled out as š.

The case of the C2P sized roots reveals an interesting aspect of the nanosyntactic framework. Standardly, an emergence of a head in the morphosyntactic structure goes hand in hand with the emergence of a morpheme realising that head. This is the case, for instance, in the š-í → ěj-i class: the presence of the extra LOADV head in the adverb leads to the emergence of ěj (recall (32)). However, sometimes, the opposite happens, i.e., we find cases where the presence of more features in the morphosyntactic structure leads to the disappearance of a morpheme. This is so in the current case. Here the presence of the LOADV head in the structure leads to an effect where the adverb root can spell out C2, and the adverb as a consequence lacks š. In the adjective, the root cannot spell out C2 because of the constituency issue (the adjectival C2P is not a subconstituent of the lexical entry). The morpheme š therefore appears in the adjective only (despite the fact that the adjective has fewer heads).

The three classes of Standard Czech thus correspond to three root sizes: AP, C1P, and C2P. This does not exhaust the logical options: there could be roots of size LOADVP. Such roots would give rise to a fourth pattern (absent from Standard Czech): š-í → i. In Section 5, we shall see that there exist dialects of Czech that have exactly this pattern.

Summarising the discussion of Standard Czech, we conclude that once the LOADV head is added in the structure, it is possible to formulate an analysis that resolves the two puzzles we encountered. First, it provides a natural solution for the puzzling š-í → ěj-i class, where ěj emerges in the adverb due to the need to realise the LOADV head. Second, it provides the analytical space for the two different comparative-adverb markers (i and ě), such that each marker has a different specification (C2+HIADV for i vs. HIADV for -ě). In the next section, we show that this analysis also provides for a neat approach to dialect variation in Czech.

Dialect variation

This section shows that a structure with two adverb heads also leads to a natural account of dialectal variation in comparative-adverb formation. Recall first that in the standard language, adverbs are marked by two different vocalic endings; see the leftmost column in In a number of Czech dialects, these vocalic endings are absent (Balhar et al. 1997: 379) and comparative adverbs are only marked suprasegmentally, namely by palatalisation and lengthening. Since the adverbial forms diachronically had a vocalic ending (Kosek 2014: 95-6), we call these the Apocope Dialects. The loss of the final vowel affects the marking of the comparative degree in rather complex ways.

In this section, we zoom in on East and Central Morava dialects (Sections 5.1 and 5.2 respectively). Since these dialects lack the final vowel, they also lack the Standard-Czech distinction between i and -ě, minimally on the surface. However, we argue that they also lack the distinction at a deeper level, in the sense that there has been paradigm levelling resulting in the loss of the Standard Czech distinction, as shown by the shading in (35). What Table (35) also intends to show is the different direction of the levelling: East-Morava has generalised the equivalent of standard i (the marker of C2+HIADV), whereas Central-Morava has generalised the equivalent of standard ě (the realisation of HIADV). This single point of difference interacts with the proposed structures in a way that all the surface differences follow from this.

East Morava

In this section, we discuss adverbs in the East Morava dialect group. Our main point is to show that East Morava dialects have a uniform comparativeadverb marker, which is the counterpart of the standard i. The relevant facts are provided in Table ( 36) on the left. For ease of comparison, the classes are organised as in the standard language (we list the standard forms on the right). 10 (36)

East Morava dialect group (data from [START_REF] Hlubinková | Stupňování adverbií, zvláště ve východomoravských nářečích [Grading of adverbs, especially in East Moravian dialects[END_REF][START_REF] Hlubinková | Tvoření deadjektivních adjektiv, zvláště ve východomoravských nářečích [Formation of deadjectival adjectives, especially in East Moravian dialects[END_REF])

East Morava Standard Czech CMPR ADJ CMPR ADV GLOSS CMPR ADJ CMPR ADV tepl-ej-š-í tepl-éj 'warm' tepl-ej-š-í tepl-ej-i ti(š) -š-í tiš-éj 'silent' tiš -š-í tiš-ej-i dra(š) -š-í dráž 'expensive' draž -š-í dráž -e
The table shows that there is no significant morphological difference between East Morava and the standard language regarding the adjectival comparatives. However, we can see that the adverbial forms lack the final vowel.

The absence of the final vowel does not entail the absence of marking: we can see that adverbs in East Morava always lengthen the final consonant, either of the suffix or the root (tepl-éj, dráž). Moreover, if they end in a non-palatal consonant (drah-ý 'expensive'), they are palatalised (dráž). 11

10 The forms are given in orthographic form, since the main focus here are not the phonetic details of the dialects, but the morphological structure of the form. 11 The lengthening of -ěj to -éj is subject to variation within East Morava (short adverbial forms are also found). [START_REF] Hlubinková | Stupňování adverbií, zvláště ve východomoravských nářečích [Grading of adverbs, especially in East Moravian dialects[END_REF] gives forms such as tepl-éj/tepl-ej 'warmer.' This contrasts with adverbs such as dráž 'more expensively,' which are never short (*draž). We analyse this as a matter of phonology, because it is independently known that the palatalising ě often prevents lengthening in contexts where all other vowels show length alternations. For instance, [START_REF] Caha | The syntax and phonology of Czech templatic morphology[END_REF] observe that infinitives with a single vowel always lengthen (e.g., pi-l 'drank' has the infinitive pí-t 'to drink'), but if that vowel is ě, it often fails to lengthen (pě-l 'sang' has the infinitive pě-t 'to sing'). We therefore assume that morphologically, all comparative adverbs lengthen, but ěj adverbs may fail to show length for phonological reasons. Now since in East Morava, lengthening applies to all adverbs, this makes it tempting to propose an analysis with a uniform marking of comparative adverbs, which we show as PAL+µ in Figure 2. This uniform adverbial marker always involves palatalisation in addition to lengthening. Palatalisation cannot be directly observed in the adverbs ending in -éj, since -j is already palatal, but we can observe palatalisation whenever the base ends in a consonant that can be subject to it (e.g., drah-ý 'expensive' dráž 'more expensively'). Other than having a single comparative-adverb marker (PAL+µ), the East-Morava dialects have a very similar type of pairing between adjectives and adverbs as Standard Czech, with a clear intermediate class that lacks ěj in the adjectival comparative, but acquires ěj in the adverb. The main point of our analysis is to show that all these classes can be captured assuming a uniform comparative-adverb marker (PAL+µ) that lexicalises C2+HIADV, which means that it has the same specification as the standard i.

Let us start the analysis with the ěj-š-í → -éj class. This class is based on AP-sized roots. In (37), we see the adjective, and (38) gives the adverb. The lexicalisation is the same as in the standard language, the only difference being the phonological realisation of C2+HIADV.

PAL+µ

The final class of roots (š-í → PAL+µ) could be of size C2P (as in the Standard), but since a dedicated HIADV marker like standard ě is missing in East Morava, a C2P size root would still pair with the uniform adverb marker PAL+µ. For simplicity, we therefore assume that the roots in question are of the size LOADVP, as we show in ( 41) and ( 42).

PAL+µ

This concludes the analysis of the three classes in East Morava Czech. The main point was to show that if we assume a uniform non-segmental PAL+µ ending, the analogue of Standard Czech i, we can easily capture the facts as they are found in East Morava dialects. Aside from the absence of a segmental adverb marker, East Morava differs from Standard Czech only in the size of the roots of the third class, which are of size LOADV rather than C2P. In the following section, we turn to Central Morava dialects.

Our main idea is that the non-segmental ending in Central Morava is the analogue of the standard ě, spelling out just HIADV.

Central Morava adverbs

In this section, we discuss comparative adverbs found in Central Morava Czech.12 This dialect group differs from both the standard language as well as the East Morava dialects discussed in Section 5.1 in two important respects. First, it maintains š in the comparative adverb (except in class IV; see the third column in ( 43)). It is also the only dialect type that distinguishes four different classes of roots when it comes to comparative formation.

The main set of facts that we aim to explain are given in The first class is exemplified by the adjective chab-ý 'weak.' The comparative adverb chab-ěj-š illustrates that in this dialect, adverbs corresponding to ěj-š-í comparatives maintain both ěj and š in the adverb. Apparently, there is no overt adverbial ending, but this does not automatically mean that morphologically speaking, there is no adverbial marking. Possibly, the marking may be non-segmental, namely lengthening, which, however, fails to lengthen the palatalising -ě (as discussed in footnote 11).

The second fact that makes Central Morava dialects different is that š-í comparatives do not have two corresponding adverbs, but three. These correspond to classes .

Class II has an adjectival š-í comparative paired with an adverb in ěj-š. The adverb thus looks the same as the adverb corresponding to an ěj-š-í adjective (as highlighted by the dark shading). We have already encountered this intermediate class before both in Standard Czech and in East Morava.

Another familiar pattern is found in Class IV. The adverb dráž 'more expensively' shows neither C1 ěj or C2 š, but it undergoes lengthening and palatalisation (which we take to be a non-segmental realisation of the comparative-adverb function). On the bottom row of Table (43), we also include the suppletive adverb líp 'better,' which belongs in the same class. We include it because this adverb makes it clear that there is no C2 ending š. This is a point that may be spurious in the case of dráž 'more expensively,' because one could argue that this is an effect of degemination, and that the underlying morphological structure is dráž-š. In this context, líp 'better' is a clearer instance of this class, since there is nothing phonologically odd about the ungrammatical *lípš (certainly, there is no need for degemination here). Note, however, that the root of the adverb 'better' líp is lengthened (the comparative adjective being lep-). Palatalisation has no effect on the labial.

The final class of š-í adjectives is represented by the root slab-ý 'weak' on row III. This root has the adverb sláb-š, which preserves the C2 marker š, while the root also lengthens. This is a new class, which is not found in Standard or East-Morava Czech.

Figure 3 summarises the four patterns. 43) (where we observe lengthening), but indirect in the case of Classes I and II. These classes have the ěj-š ending, and -ě is immune to lengthening (as we have argued in footnote 11). We nevertheless assume that the same comparative-adverb marker is present here too, maintaining the idea that upon losing the segmental endings, the evidence for a distinction between two different adverbial endings is lost, and a single comparative-adverb marker appears in its stead. We shall argue that in Central Morava, this marker is the realisation of HIADV, i.e., the counterpart of the Standard -ě. This idea is going to explain why comparative adverbs in this dialect acquire š in Classes I-III. Figure 3 represents the most complex system found in the Czech dialects, and our goal will be to explain both the allomorphs found, and the pairing between adjectives and adverbs, which requires us to operate with four different classes of roots. Our idea is that the four classes of adjectiveadverb pairs can be derived under the hypothesis that each class is based on a root of a different size, as shown in (44). The structure of the comparative adverb is provided in (46). The suprasegmental ending only spells out HIADV, which leads to the emergence of š under C2. The morpheme ěj spells out C1 and LOADV, as it does in all other varieties. Let us now turn to roots of size C1P (Class II). In the adjectival structure, these roots spell out C1P, and they therefore do not need ěj: their adjectival comparative is just š-í. However, in the adverb structure, these roots still need ěj, because something must realise the LOADV head. The rest of the structure is spelled out as in ( 46). In sum, roots of the size C1P give rise to the š-í → ěj-š pattern, with ěj appearing due to the low adverb head. Roots of size LOADVP (Class III) give rise to the š-í → š pattern. We show this in ( 49) and ( 50). Starting with the adverbial structure (50), we see that with these roots, there is no need for the marker ěj, since the root lexicalises the LOADV feature, which triggered the presence of ěj in the adverbs that have it. However, the root requires the presence of š, and it also lengthens, e.g. slab-š-í → sláb-š 'weaker'. The very same root can also spell out just C1P in the adjectival structure (49), because this is a sub-constituent of the LOADVP; hence, spellout of C1P in ( 49) is allowed by the Superset Principle. The comparative marker ěj remains absent here too since the root lexicalises C1. Finally, Class IV roots are of size C2P (where this C2P includes the LOADV head). They do not need either ěj or š in the comparative adverb, as shown in (52). They only undergo lengthening and palatalisation (recall from (43) the length difference between draž-š-í → dráž 'more expensive'; or lep-š-í → líp 'better'). In the comparative adjective in (51), the root spells out only C1P, and C2 is therefore spelled out as š. The root cannot spell out C2P in the adjectival structure (51), since this is not a sub-constituent of the root's lexical entry.

The lexical entry of the root corresponds to the adverbial C2P, and since the adjectival C2P lacks LOADV, it is not a subconstituent of the adverbial one. As a result, the root can only spell out C1P in the adjective, and this leads to the emergence of š under C2 in (51).

Summary

This section has shown that the system developed to handle Standard Czech (with two adverb heads and a split comparative) can be extended to capture various dialects of Czech. The main idea of the analysis is that due to the lack of a segmental ending, the dialects use a single non-discriminate adverbial ending. Our idea is that in some dialects (exemplified by East Morava), the single surviving ending is the counterpart of the standard i. In other dialects (Central Morava), it is the counterpart of ě. Different types of adverbial marking arise as an automatic consequence of this simple distinction. The final point we want to stress regarding this section is that the rich structure with two adverb heads and a split comparative allows us to capture the fact that there are four different classes of roots in Central Morava. The rather complex system of pairing between adjectival and adverbial comparatives in this dialect falls out as an effect of root size, with no need to say anything special beyond characterising the individual roots in terms of what features they are capable of realising.

Conclusions

In this article, we investigated the complex system of pairing between comparative adjectives and comparative adverbs in Standard Czech and Czech dialects. We have provided a formal model of how this pairing is achieved for each variety, and we have also identified a plausible source of differences among the varieties: while Standard Czech has two different endings (i and e), the dialects only have a single ending. This single ending came to exist due to paradigmatic levelling on the one hand, and phonological erosion on the other, whereby the segmental vocalic adverbial endings got eliminated in the dialects. The difference in the direction of the levelling lead to different systems of adverb formation. We could achieve this result by adopting the following ideas.

(53) a. The comparative meaning is distributed across two projections, C1 and C2 b. There is both a low and a high adverbial head c. Lexicalisation targets non-terminals. Which lexical item realises which head is determined by the Spellout Algorithm of Starke (2018) d. Roots belong to different classes. These can be modelled by attributing to each root a different number of functional features in the lexicon Once these assumptions are adopted, the allomorphs that each root combines with in the adjectival and in the adverbial comparative are a function of the root's specification, in combination with the proposals (53ac). As a final note, we observe that in achieving this result, the proposal does not rely on complex context-sensitive rules. Consider, for instance, the distribution of -ěj in adjective-adverb pairs such as draž-š-í -dráž-e 'more expensive' and slab-š-í -slab-ěj-i 'weaker.' On the surface, we observe the following: 'C1 (the position of exponence for ěj) is always realised as zero when attached to roots such as drah; but with the root slab, it is zero only if the form is an adjective, but not an adverb. Else, C1 is realised as ěj.' Thanks to phrasal lexicalisation, zero morphemes (with such complex distributions) play no role in our account, which we take to be a notable achievement of the analysis.

  adverbs (š-í adjectives, Class 1)

  Figure 1: Adjective-adverb pairs in Standard Czech

  ) (repeated from (23)).(28)Three classes of comparative ADJs/ADVs in Standard CzechCMPR ADJ CMPR ADV GLOSS chab-ěj-š-í chab-ěj-i 'weak' slab-š-í slab-ěj-i 'weak' draž-š-í dráž-e 'expensive'We begin with the ěj-š-í → ěj-i class on the top row. The roots of this class are lexically specified as APs. The structure of the comparative adjective is given in (

Figure 2 :

 2 Figure 2: Adjective-adverb pairs in East Morava

  the š-í → -éj class is also analogous to the standard, and it is based on roots of the size C1P. The structures are shown below in (39

Figure 3 :

 3 Figure 3: Adjective-adverb pairs in Central MoravaIn the figure, we are again assuming that all classes have a uniform comparativeadverb marker, namely PAL+µ. The evidence for this marker is direct in Classes III and IV of Table (43) (where we observe lengthening), but indirect in the case of Classes I and II. These classes have the ěj-š ending, and -ě is immune to lengthening (as we have argued in footnote 11). We nevertheless assume that the same comparative-adverb marker is present here too, maintaining the idea that upon losing the segmental endings, the evidence for a distinction between two different adverbial endings is lost, and a single comparative-adverb marker appears in its stead. We shall argue that in Central Morava, this marker is the realisation of HIADV, i.e., the counterpart of the Standard -ě. This idea is going to explain why comparative adverbs in this dialect acquire š in Classes I-III.Figure3represents the most complex system found in the Czech dialects, and our goal will be to explain both the allomorphs found, and the pairing between adjectives and adverbs, which requires us to operate with four different classes of roots. Our idea is that the four classes of adjectiveadverb pairs can be derived under the hypothesis that each class is based on a root of a different size, as shown in (44).

  look at the individual patterns. We begin with the AP-sized roots (Class I). Such roots always need both ěj and š, yielding the ěj-š-í → ěj-š pattern. The structure of the comparative adjective is given in (45), C1 is spelled out by ěj, and C2 by š.

  13

  Let us now turn to the class of adjectives that only have š in the comparative. With these adjectives, C1 remains unexpressed in the surface string. A standard way to express the fact that C1 is silent is to propose that it is realized by a special zero allomorph of ěj, see (8). The insertion of the zero would be only available in the context of selected roots, which is encoded by the rule (9).

	(9)	A context-sensitive rule C1 ⇔ Ø / { √ SLAB, ...}
	Building on Starke (2018), Caha et al. (2019) propose an alternative view based on the idea that lexical items (including roots) may lexicalise more than just a single terminal node. Specifically, roots that combine with š are proposed to lexicalise not only the adjectival core of the meaning (that is, AP), but also C1. This is depicted in (10), where the root slab-'weak' lexicalises a non-terminal node containing C1P, which contains C1 and AP. As a result, C1 is realised by the root, and the fact that the suffix -ěj is absent with these roots follows automatically.
	(10)			AGRP	(11)		AGRP
				C2P	AGR		AP	AGR
		slab 'weak'	C1P AP . . . C1	C2 š	í	3	. . . slab 'weak'	ý
	(7)			AGRP	(8)			AGRP
				C2P	AGR			C2P	AGR
			C1P		C2				C1P	C2
		AP		C1				AP	C1
		chab ('weak')	ěj	š	í	slab ('weak')	ø	š	í

Table (

 (

		23).
	(23)	Three classes of comparative ADJs/ADVs in Standard Czech CMPR ADJ CMPR ADV GLOSS
		chab-ěj-š-í slab-š-í draž-š-í	chab-ěj-i 'weak' slab-ěj-i 'weak' dráž-e 'expensive'

We can see that the system is descriptively simple (though analytically challenging, as we already mentioned). There are roots which always show ěj (top row, dark shade). Then there are roots which never show ěj (bottom row, light shade). And finally, there are 'intermediate' roots, which pattern with the ěj-less roots in the adjective, but with the other class in the adverb.

  There are reasons to think that ago (like the Karelian mpi) is the realisation of C2[START_REF] Holaj | Who is afraid of a non-local wolf? Talk presented at CRAFF[END_REF]. If that is so, the facts in (26) give us reasons to think that the adverbial ki is lower than C2.To see why[START_REF] Holaj | Who is afraid of a non-local wolf? Talk presented at CRAFF[END_REF] treat ago as C2, consider the suppletive pair on 'good' and hobe 'better,' given on the first row of Table (26). Since hobe does not combine with any overt comparative marker,[START_REF] Holaj | Who is afraid of a non-local wolf? Talk presented at CRAFF[END_REF] analyse it as lexicalising both C1 and C2. However, in forms featuring the marker xe 'a little bit,' hobe and ago do combine, yielding the form hobe-xe-ago 'a little bit better,' see (27).

			POS	'new'	CMPR	: 119) 'good' POS CMPR
		ADJ berri ADV berri-ki	berri -ago on berri-ki-ago on-gi	hobe hobe-ki
	(27)	hobe better.C1	-xe -bit	-ago -C2

[START_REF] Holaj | Who is afraid of a non-local wolf? Talk presented at CRAFF[END_REF]

suggest that xe comes in between C1 and C2. Its intervention prevents hobe from lexicalising C2, and ago is therefore inserted. The suppletive root hobe realises just AP+C1 in (27) (which is allowed by the Superset Principle).

  Table (35).

	(35)	Dialectal Variation in Czech Standard Apocope Dialects Czech East Morava Central Morava
		i ě	PAL+µ	PAL+µ

  Table (43). The table presents the four classes under roman numbers (I-IV), with Class IV exemplified by two adjectives.

	(43)	Central Morava comparative adjectives and adverbs POS ADJ CMPR ADJ CMPR ADV GLOSS
		I. II. III. IV.	chab-ý chab-ěj-š-í hrub-ý hrub-š-í slab-ý slab-š-í drah-ý draž-š-í dobr-ý lep-š-í	chab-ěj-š 'weak' hrub-ěj-š 'rough' sláb-š 'weak' dráž 'expensive' líp 'good'

There is a small class of adjectives that have a complex base ending in -k, e.g., leh-k-ý 'easy,' with the comparative leh-č-í 'easier.' This form can be interpreted as a zero-derived comparative, where the final agreement marker triggers palatalisation of the -k suffix (lehk-í → leh-č-í). However, it is unclear how these forms are derived, since an underlying sequence of morphemes leh-k-š-í would also be realised as leh-č-í in Czech, as a result of palatalisation and degemination[START_REF] Caha | The fine structure of the comparative[END_REF]). We set these adjectives aside here.

[START_REF] Křivan | Komparativ v korpusu: explanace morfematické struktury českého stupňování na základě frekvence tvarů [Comparative in the corpus: explanation of the morphematic structure of Czech gradation based on the frequency of forms[END_REF] concludes that frequency plays a role, with more frequent roots showing preference for š, as opposed to ějš.

In the semantics literature, a complex meaning for the comparative has been proposed, for instance, in[START_REF] Kennedy | Measure of change: The adjectival core of degree achievements[END_REF]. In their approach, the adjective base corresponds to a measure function, from which a derived measure function is constructed in the comparative, followed by the application of a POS head that turns the derived measure function into a property.

[START_REF] Caha | The fine structure of the comparative[END_REF] use pointers as a way of linking two suppletive roots to each other. We do not discuss pointers here for reasons of space.

The Superset Principle implies that lexicalisation is subject to a constituency requirement. The astute reader will notice that the C2 and ADV heads in (19) do not form a constituent which excludes the other heads. The reason for this is that we depict lexicalisations in an informal way using a brace. In actual fact, lexicalisation is driven by the Spellout Algorithm[START_REF] Starke | Complex left branches, spellout, and prefixes[END_REF]. Application of this algorithm will require C1P to move from within the AdvP, so that C2 and Adv form a constituent. For reasons of space, we ignore these technical details.

This follows from the so-called Spellout Algorithm[START_REF] Starke | Complex left branches, spellout, and prefixes[END_REF]).

It is not clear why 'quick' and 'good' use slightly different shapes of the functional morphemes. A possible explanation is that Bobaljik relies on multiple sources for Karelian, as revealed by the appendix of his book.

It is possible to assume that Basque and Karelian have both Adv heads, even though they do not show morphological evidence for this. For instance, if we specify the Basque -ago as spelling out [C2+HIADV], it will function both as a comparative marker in the adjective (spelling out just C2), or as a comparative adverb marker (spelling out C2+HIADV, with the low adverb head realised as ki). As a result, Basque can be analysed as Czech with both hi and low ADV. A similar analysis can be devised for Karelian, where the root can be assumed to spell out not only AP+C1, but also LOADV. We do not elaborate this analysis here as it is orthogonal to our main concern.

In the adverb, the C1 feature could in principle be lexicalised by either the root or the -ěj suffix. The spellout algorithm dictates that in such a case, the root only spells out AP. The ěj suffix lexicalises the remnant constituent [ LOADV [C1]], out of which the AP (lexicalised by the root) extracts. Technically, the derivation requires backtracking[START_REF] Starke | Complex left branches, spellout, and prefixes[END_REF].

Similar facts are also found in West Bohemia.

The raising of e to i under lengthening is productive in most Czech dialects, including Central Morava, and we are thus assuming that líp 'better, ADV' is a lengthened version of the adjectival root lep. Alternatively, we could also analyse lip as a suppletive adverbial root spelling out C2P (including the LOADV head), while lep would be just C1P.