Tone is distinct from other phonological phenomena both qualitatively and quantitatively (Hyman 2011), and has been instrumental in shaping phonological theory in many ways. However, the contributions to current linguistic theory of “grammatical tone’ (GT) – a type of non-concatenative morphology where a morpheme is expressed at least in part by tone and/or tone changes – have been less apparent. In this paper, we take stock of the types of GT patterns attested in the literature and the different theoretical treatments of GT that have been proposed to date. We show that GT is still to a large extent underexplored, and highlight the immense potential of the study of GT for improving our understanding of phonology and its outer limits. This paper serves as an introduction to the high-quality research articles collected in this special issue, which directly address how GT critically informs phonological theory and its current developments.

This article considers the question of what constitutes item-based morphology, with a specific look at grammatical tone. Numerous case studies of grammatical tone are examined in light of the debate on whether morphology is item-based or process-based. In each case, tonal alternations are an exponent, sometimes the sole exponent, of some grammatical feature. Two of the case studies are examples of grammatical tone that can straightforwardly be analysed as involving concatenated morphophonological forms; however, in other cases, the grammatical tone cannot be reduced to the concatenation of a tonal affix or phonological feature with some stem. The latter type cannot straightforwardly be analysed as item-based, but if still phonologically predictable and productive, is not satisfactorily analysed as suppletive. This article suggests a set of diagnostics that can be used to determine whether a given phenomenon is best analysed as item-based, process-based or suppletive. Then, an analysis is presented in Cophonologies by Phase (CbP), where morphosyntactic features can be mapped not only to underlying phonological items, but also to morpheme-specific constraint weight adjustments. CbP allows for what may have been traditionally called item-based and process-based morphology to co-exist in a single framework.

Dagaare is a language of northern Ghana and adjoining areas of Burkina Faso. There are two tones, H and L, and contrastive downstep H!H that involves a non-automatic pitch drop between two H tones. The challenge is to explain the extensive morphological conditioning of tonal processes, including dissimilation, downstep and spreading. Our solution involves level ordering: tones are introduced at different morphological levels (stems, words and phrases) and later processes can make earlier processes opaque. Tonal differences between nouns (spreading) versus verbs (no spreading) and stems (dissimilation) versus words (downstep) arise from constraint ranking differences within and across levels. There are two kinds of downsteps: stem-level downsteps are underlying L tones affiliated with some morpheme; word-level downsteps are L tones inserted by a general process of word-final lowering. Only one downstep per word is allowed. If more would arise, the morphologically inner downstep blocks the morphologically outer downstep.

Grammatical tone (GT) can be the sole exponent or a co-exponent of grammatical meaning (Hyman 2012; Rolle 2018), but there has been little discussion of how they distribute within a single language. In this article, I explore the relationship between tonal and segmental materials in Gyeli (Bantu A801, Cameroon), adopting a property-driven approach to phonological typology (Plank 2001; Hyman 2009). Gyeli has eight GTs in simple predicates, which serve as sole exponents of tense, aspect, mood and polarity distinctions and object-marking. When GT is a co-exponent accompanied by segmental material, for example, in auxiliary constructions, the information that the tonal component contributes to the meaning is insufficient to distinguish between grammatical categories: its functional load is weak. The decrease in functional load is correlated with an increase in length of a segmental co-exponent. This can be explained by the tonal cophonologies of segmental morphemes and their different GT dominance types.

A major issue in Bantu morphophonology is how to get the right tones in the right ‘cells’ in the verb paradigm. In many Bantu languages, grammatical tones are assigned to different positions in the verb stem depending on inflectional features of tense, aspect, mood (TAM), polarity and clause type: The same TAM may assign different tones (and different segmental allomorphs) in the affirmative vs. negative and in main vs. relative clauses. Although such ‘melodic tones’ (Odden & Bickmore 2014) are typically restricted to the verb stem (root + suffixes), often also the domain of vowel harmony and other segmental phonology, both the presence and mapping of grammatical tones within the stem cannot be determined without reference to the prefixal inflectional marking of subject, negation, TAM and object which precede the stem. In this article, we discuss three cases in Ekegusii, a Bantu language of Kenya, that require the stem-assigned grammatical tones to look ‘outward’ to morphological and phonological properties of such prefixes: (1) differential mapping according to whether the pre-stem tone-bearing unit is toneless, a derived H(igh) (from H-tone spreading), or underlyingly /H/ (Bickmore 1997, 1999); (2) presence of an object prefix in imperative and subjunctive forms and (3) initial/final tone agreement between the subject prefix and the final vowel of the verb (cf. Rolle & Bickmore (2022). We will show that Ekegusii provides extensive evidence that both the presence of grammatical Hs and their specific mapping, while targeting the stem (root + suffixes), must be ‘globally’ calculated on the basis of the entire morphosyntactic structure of the verb (including features exponed by prefixes).

Amuzgo (Otomanguean: Mexico) has a large inventory of lexically arbitrary tonal inflection classes in person/number paradigms, where inflectional tones overwrite the root's lexical tone. In causatives, however, inflectional tones are predictable from phonological properties of the root, primarily lexical tone. The inertness of root inflection classes in causatives is argued to follow from cyclicity: once the causative Voice head triggers spell-out, lexical inflection-class specifications are no longer visible, and only phonological information can condition allomorphy in the outer domain of person/number agreement. The grammatical behaviour of inflectional tone thus reflects its structural morphosyntactic position, as distinct from its linear phonological one. I distinguish between several possible analyses of phonologically conditioned tonal-overwriting allomorphy, and propose that the Amuzgo case involves constraint-mediated competition among a priority-ranked list of allomorphs in the input, rather than creation of tonal allomorph candidates purely within the phonology or subcategorisation frames in the lexical representations of allomorphs.