2.3.1. Survey of crazy rules

A crazy rule is one that does not make sense phonetically speaking, that is, which is not “natural”. Since Bach and Harms (Reference Bach, Harms, Stockwell and Macaulay1972), a small literature on crazy rules has arisen that documents particular cases such as i → u / d__ (for Southern Pomoan, see Buckley Reference Buckley2000, Reference Buckley2003) (Vennemann Reference Vennemann, Stockwell and Macaulay1972, Hyman, Reference Hyman, Hume and Johnson2001). Chabot (Reference Chabot2021) has drawn an inventory of cases mentioned in the literature. A relevant generalization is that crazy rules appear to only ever be melodically crazy (see also Scheer Reference Scheer, Honeybone and Salmons2015: 333ff). That is, in a crazy rule A → B / C, A and B are only ever items that occur below the skeleton. There do not appear to be crazy rules that manipulate items at and above the skeleton: compensatory shortening, closed syllable lengthening (see section 2.3.2), tonic shortening etc. (syllable structure) or anti-Latin stress (stress falls on the antipenultimate syllable except when the penultimate syllable is short, in which case this syllable is stressed) are not on record.

But crazy rules not only appear to spare items at and above the skeleton: they also seem to make no reference to them in the conditioning context: i → u / d__ is reported for Southern Pomoan, but rules like p → r in coda position, or p → r after tonic vowels do not appear to occur.Footnote ¹⁴

Of course Chabot's (Reference Chabot2021) sample of crazy rules is incomplete and there is no guarantee that there are no syllabically or stress-wise crazy rules out there. But given the arbitrary and incomplete sample, there is no reason for all documented cases to accidentally concern only melodic properties.

Therefore the absence of crazy rules concerning syllable and stress properties is likely to be significant. This absence is exactly what is predicted by SFP: the computation of phonologically meaningless items (alphas and betas that occur below the skeleton) is arbitrary (see (2b)), but the computation of phonologically meaningful items (at and above the skeleton) is not.

2.3.2. There is no closed syllable lengthening or open syllable shortening

The notions closed syllable lengthening and open syllable shortening are frequently misunderstood. What is meant are processes whereby the syllabic position causes the effect observed, just as in regular closed syllable shortening, where shortening is specifically triggered by closed syllables, and by no other factor. That is, it occurs in all closed syllables and only in this environment. A valid closed syllable lengthening (or open syllable shortening) will thus be a process whereby all short vowels lengthen specifically in closed syllables and nowhere else (or all long vowels shorten specifically in open syllables and nowhere else).

Of course, there are cases where vowel lengthening in closed syllables occurs but is not caused by syllable structure. A recurrent pattern of this kind is due to voice-induced vowel lengthening whereby short vowels lengthen before a voiced consonant, which may be a coda. This pattern is found in German, in the evolution of Western Slavic (Scheer Reference Scheer2017), in English (where it may be called pre-fortis clipping) and beyond (Chen Reference Chen1970, Klatt Reference Klatt1973). Like other processes, it has a phonetic origin and may be phonologized in systems with distinctive vowel length (like German or Czech). When vowels lengthen before voiced consonants that happen to be codas, there is of course no closed syllable lengthening, since closed syllables play no role in the causality of the process.

In this context, an interesting case is reported from Menomini (Algonquian). In this language where vowel length is distinctive, Bloomfield (Reference Bloomfield1939) describes vowel length alternations that respond to a complex set of conditioning factors.Footnote ¹⁵ In §32 of the article, Bloomfield reports that “if the even (second, fourth, etc.) syllable after the next preceding long vowel or after the beginning of a glottal word, is open and has a long vowel, this long vowel is replaced by short.” Conversely, “if the even syllable (as [defined] in §32) is closed and contains a short vowel, this short vowel is replaced by a long” (§33). Glottal words are those “whose first syllable contains a short vowel followed by ʔ” (§31). That is, in order for a long vowel to shorten in an open syllable, or for a short vowel to lengthen in a closed syllable, the syllable at hand must be even-numbered with respect to the next long vowel to its left, or to the beginning of the word in glottal words. The even-numbered condition is translated into “head of a disyllabic (iambic) foot” by Hayes (Reference Hayes1995: 219), but this is not obvious, since the calculus is not based on the left word edge (except for glottal words), but rather on the next preceding long vowel.

In any case, the Menomini process described does not qualify as closed syllable lengthening or open syllable shortening, since the causality is multi-factored: it is not the case that all long vowels in open syllables undergo shortening, or that all short vowels in closed syllables lengthen.

2.4.1. Below and above the skeleton

SFP thus produces a situation where an arbitrary and a non-arbitrary phonology coexist in the sense of (2a) (objects), and (2b) (the computation of these objects). Arbitrary phonology occurs below, non-arbitrary phonology at and above the skeleton in a regular autosegmental setting. This is shown under (3), which also mentions a consequence of the fact that only items below the skeleton have a phonetic correlate: these, but not items at and above the skeleton, are spelled out. This is because spelling out an item is the process of assigning it a phonetic value: items at and above the skeleton cannot be spelled out, because they do not have any phonetic correlate (more on this in section 6).

For the time being, the two phonologies are i) taken to be static (i.e., areas in the autosegmental representation, computation therein is discussed below) and ii) are called Phonology I and II. They occur in a box called production phonology under (3), referring to the computation that turns an underlying (lexical) representation into a surface representation (which is then subject to spell-out). It is opposed to lexicalization phonology, to be introduced in section 3, which includes those phonological operations that occur upon the lexicalization of morphemes, that is, when the acoustic signal is transformed into a lexically stored item. The setup under (3) will be refined as the discussion unfolds.

The coexistence of an arbitrary and a non-arbitrary phonology has an obvious consequence: we are dealing with two distinct computational systems, that is, two distinct modules. Computation within a single module could not possibly be arbitrary and non-arbitrary at the same time, or build phonologically meaningful items (onsets, feet etc.) on the basis of phonologically meaningless primes (alphas, betas, gammas).Footnote ¹⁷

The existence of two distinct phonological modules in production raises the non-trivial questions under (4) below.

In both cases under (4), the communication between the two phonologies is non-arbitrary: syllable structure is not just anything and its reverse, given (segmental) sonority, and the lenition / fortition that is visible on segments is not random (lenition occurs in weak, not in strong positions).Footnote ¹⁸

2.4.2. Modular workings

The previous section has drawn the conclusion that there must be two distinct computational systems in phonology, hosting phonologically meaningless and meaningful items, respectively.

Space restrictions precluding more detailed discussion of modularity, the following merely mentions some relevant properties. Fodorian modularity (Fodor Reference Fodor1983) expresses the insight that computation in the mind/brain is not all-purpose, but rather falls into a number of specialized systems that are designed to carry out a specific task. Computational systems are thus competent for a particular domain and can only parse information pertaining to this domain (domain specificity): their input is restricted to a specific vocabulary. That is, foreign vocabulary is unintelligible and communication with other modules requires a translational mechanism (spell-out). Humans are predisposed to develop modules for specific domains: the information that there will be a computational system for vision, audition, etc. (but not for filling in a tax declaration or playing the piano) is genetically coded and present at birth. Relevant literature includes Segal (Reference Segal, Carruthers and Smith1996), Coltheart (Reference Coltheart1999), Gerrans (Reference Gerrans2002), Jackendoff (Reference Jackendoff2002) and Carruthers (Reference Carruthers2006: 3ff).

Modules are thus computational systems that take a domain-specific vocabulary as an input, carry out a computation and return structure. For example, syntactic computation (Merge) operates over number, person, animacy etc. and builds hierarchical structure, the syntactic tree. In this article, vocabulary items are called primes, and the result returned by computation based on them, is structure. Hence the computation that takes sonority primes (Son) as an input returns structSon (syllable structure, feet, etc.), and the same goes for Place primes (StructPlace) as well as Lar primes (StructLar).

4.1.1. To be heard vs. to be understood

Harris (Reference Harris2006) argues that Son is different in kind with respect to Place and Lar. Observing that “sonority differences are never contrastive in the way that differences defined in terms of individual features can be”, he argues that phonetically speaking, “speech is a modulated carrier signal: the modulations bear the linguistic message, while the carrier enables the message to be heard.” That is, the carrier signal, sonority, “is concerned primarily with the audibility of the linguistic message rather than with the message itself” (all quotes from Harris Reference Harris2006: 1484). Thus sonority is about being heard, while place and laryngeal properties are about being understood: they carry the linguistic message that sonority is not conveying.Footnote ²⁵

4.1.2. Selective bottom-up visibility

It is a trivial, though rarely explicitly stated fact that Son is projected above the skeleton, while Place and Lar are not. Syllable structure is a function of two and only two factors: the linear order of segments and their relative sonority. That syllable structure depends on these two factors (plus parametric settings determining whether or not specific syllabic configurations such as codas, branching onsets etc. are provided for) and on no other is an undisputed and theory-independent fact which is transcribed in all syllabification algorithms (e.g., Steriade Reference Steriade1982: 72ff, Blevins Reference Blevins and Goldsmith1995: 221ff, Hayes Reference Hayes2009: 251ff).

That Son, but not Place and Lar, are present above the skeleton is also shown by reverse engineering. Sonority values may to a certain extent be predicted given syllable structure: onsets and codas contain low sonority items, nuclei contain high sonority items; the sonority of the members of a branching onset is rising; it is non-rising in a coda-onset sequence. By contrast, syllable structure does not allow us to deduce anything about Place or Lar properties of segments: the fact of being a nucleus, onset or coda tells you nothing about whether the segments associated are labial, palatal, velar etc., and onset- and codahood provide no clue whether segments are voiced or voiceless either.Footnote ²⁶

There is thus reason to believe that Phon I under (3), that is, items which occur at and above the skeleton, are the result of a structure-building computation that is based on (phonologically meaningful) sonority primes. That is, the domain-specific vocabulary of the Son module are Son primes, and modular computation based on them returns structSon, the items familiar from above the skeleton.

4.1.3. Selective top-down visibility

The previous section has discussed the fact that syllable structure is built without reference to Place and Lar. This indicates that the Son vocabulary on the one hand, and Place / Lar vocabulary on the other hand, are distinct: if Place / Lar primes were present and available when structSon is built, they would be expected to be taken into account. The fact that they are not suggests that they occur in a different module.

This conclusion is supported by a solid empirical generalization: processes which occur at and above the skeleton may be conditioned by Son, but are blind to Place and Lar.Footnote ²⁷ Evidence comes from linearization when the landing site of infixes is defined (see (6a)) from phonologically conditioned allomorph selection (6b), from stress placement (6c), from contour tone placement (6d) and from positional strength (6e). If the processes at hand occur in the Son module that is different from the Place / Lar module(s), it follows that they cannot see Place / Lar properties (just as syllabification is blind to them).

Note that the diagnostic for tone provided by contour tone placement (6d) appears to be consistent with the fact that tone may also influence allomorph selection (6b): Paster (Reference Paster2006: 126–130) discusses a case from the Yucunany dialect of Mixtepec Mixtec (Otomanguean, Mexico) where the first person sg is marked by a floating low tone, except when the final tone of the verb stem is low, in which case -yù is suffixed. This also ties in with the fact that tone appears to be able to influence morpho-syntactic computation, as reported by Rose and Jenks (Reference Rose and Jenks2011) (see section 5.4.2). These three diagnostics are consistent, suggesting that tone belongs to the area above the skeleton (the Son module) where it is typically located in autosegmental representations. But they conflict with the fact that tone has a phonetic correlate (pitch) and interacts with regular melodic primes (namely in Lar) (see footnote 8). The diagnostics developed in the present article thus confirm the infamous hermaphrodite nature of tone (Hyman Reference Hyman, Goldsmith, Riggle and Yu2011).

4.2.1. Perception-based sonority

Perception-based sonority is exposed by Steriade (Reference Steriade1994, Reference Steriade, Fujimura, Joseph and Palek1999). As Moreton et al. (Reference Moreton, Feng and Smith2005: 341) put it, “perceptibility theory […] says that a segment's compatibility with a given environment depends on how accurately it is likely to be perceived in that environment”, where “environment” refers to classical syllabic positions such as onset, coda and so forth. In this approach, syllable structure exists in phonological representations, but is directly abstracted from phonetic information and has no bearing on segmental alternations. That is, VTRV is parsed as V.TRV in Spanish but as VT.RV in Classical Arabic, but “consonantal phonotactics are best understood as syllable-independent, string-based conditions reflecting positional differences in the perceptibility of contrasts” (Steriade Reference Steriade, Fujimura, Joseph and Palek1999: 205). In this view, lenition and fortition are thus entirely unrelated to syllable structure, the latter however existing independently.

The question whether syllable structure is responsible for positional phenomena is unrelated to the issue pursued here, that is, the existence of Son primes and the way items, at and above the skeleton, are built. Regarding this issue, it seems to me that the perceptibility-based approach is in fact a notational variant of the regular perspective based on Son primes. When building (phonological) syllable structure based on perceptibility, the gradient phonetic signal will also need to be transformed into discrete phonological units, the segments, and it must also be somehow decided that certain segments are vowels, while others are consonants, and that the former will end up in a nucleus, while the latter are parsed into an onset or a coda. This is but a short version of the process described in section 3 and further discussed in section 5.2.3, that is, the construction of syllable structure based on the phonetic signal with an intermediate classification of segments in terms of sonority.

4.2.2. Structuralization of sonority

In SPE, major class features such as [±son], [±cons] or [±voc] were scrambled in a single feature matrix together with features defining melodic characteristics such as place of articulation and laryngeal properties. OT implements sonority along the same lines, except that scrambling concerns constraints, rather than features (e.g., Smith and Moreton Reference Smith, Moreton and Parker2012).

Departing from an amorphous and unstructured set of primes, Feature Geometry made a first step towards the structural representation of sonority. The theory introduced by Clements (Reference Clements1985) autosegmentalized the amorphous bundle of SPE features, aiming at grouping them into natural classes (class nodes) in a feature geometric tree. In this approach, sonority is still represented in terms of the SPE features (or some version thereof), but following the class node logic, features are grouped together and isolated from other classes of features. In Clements and Hume's (Reference Clements, Hume and Goldsmith1995) final model of Feature Geometry, the Son primes [±son], [±approximant] and [±vocoid] are borne directly by the root node, as opposed to other features which are represented in the feature geometric tree below the root node.

This structural insulation of sonority was further developed in a number of approaches sharing the idea that rather than being represented by specific primes, sonority is a function of Place and Lar primes as well as of their organization. Government Phonology has pioneered this line of thought: in this approach, sonority is a derived notion based on segmental complexity. That is, the more primes a segment is made of, the less sonorous it is (and vice versa) (Harris Reference Harris1990, Backley Reference Backley2011: 114ff). Segmental complexity has a number of issues: for example, it cannot derive vocalic sonority. High i,u and low a are made of just one prime (I, U and A, respectively), while mid vowels bear two primes (I,A or U,A) and should thus be less sonorous than high and low vowels, which of course is not the case.

Other implementations of the idea that sonority is a structural property include GP2.0 (Pöchtrager Reference Pöchtrager2006: 55ff, Pöchtrager and Kaye Reference Pöchtrager and Kaye2013); Rice (Reference Rice1992); Schwartz’ (Reference Schwartz2013, Reference Schwartz2017) Onset Prominence model; Hulst's (Reference van der Hulst1994, Reference van der Hulst, Durand and Katamba1995a, Reference van der Hulst, Rennison and Kühnhammer1999) Radical CV Phonology; and de Carvalho's (Reference de Carvalho2002a, Reference de Carvalho, de Carvalho, Scheer and Ségéral2008, Reference de Carvalho2017) perspective. These approaches are reviewed in greater detail in Hermans and Oostendorp (Reference Hermans, van Oostendorp, Broekhuis, Corver, Huybregts, Kleinhenz and Koster2005) and in Scheer (Reference Scheer2019b).

The visibility-based evidence discussed in sections 4.1.2 and 4.1.3 documents the exclusive reference to sonority for the processes mentioned, with Place and Lar being irrelevant and invisible. Given this situation, it would come as a surprise if sonority and melody cohabited the same space: were they all accessible, there would be no reason why some items should be selectively taken into account, while others are actively ignored. Therefore, Place and Lar information must not be accessible when sonority computation is carried out, irrespective of how sonority is represented (structuralized or in the guise of primes). Scheer (Reference Scheer2019b) thus concludes that the empirical situation regarding visibility warrants a segregation of sonority and Place / Laryngeal properties into distinct modules, rather than the structuralization of the former.Footnote ²⁹

Approaches that make sonority a structural property thus take a step in the right direction by estranging sonority from Place / Lar. But they leave all players in the same computational space (module). If a further step is taken that recognizes the segregation of Son and Place / Lar in distinct computational systems, the structural representation of sonority loses its raison d’être, which is to enact the difference.

If thus sonority is a computational system of its own, there must be Son primes, since modular computation is always based on primes (see section 2.4.2).

5.2.1. Primes are module-specific

It was mentioned in section 2.4.2 that modules are hard wired, that is, genetically coded: humans are predisposed for processing visual, auditory etc. information. If Son, Place and Lar are three distinct modules, their existence and domain of competence must thus be genetically coded and present at birth. That is, children know beforehand that these three modules exist, and that their working requires the construction of relevant primes in each domain.Footnote ³³

An argument for the existence of three distinct and universal systems is the trivial fact that all languages appear to have distinctions in all three areas: there is no language which chooses, say, to ignore the possibility of implementing Lar distinctions, or which builds a distinctive system without some contrast in Place, or where all segments belong to the same sonority class. If primes were entirely unconstrained at birth, some language could build a contrastive system where, say, laryngeal properties play no role. What is observed, though, is that while the three types of contrast are always present independently of the language-specific environment, there is variation within each system.

A consequence of there being three distinct modules is that alphas, betas and gammas are not colourless, but rather specific to the three domains at hand. That is, primes occur in a specific module and are thus different in kind. This difference may be graphically indicated by using symbols from different alphabets, say, α, β, γ for Place primes, б, г, д for Lar primes and a, b, c for Son primes.Footnote ³⁴

5.2.2. Place and Lar primes

Place and Lar primes bring together the three types of arbitrariness under (2): the primes themselves are arbitrary ((2a): α is not any more appropriate than β); their computation is arbitrary ((2b): any prime may be added to or removed from any segment, given any trigger and its reverse); and so is their association to a phonetic category ((2c): any association of any prime with anyphonetic category is possible).

Primes themselves are thus absent at birth. They are created and associated to relevant phonetic correlates upon exposure to contrast and phonological processing of the target language (e.g., Boersma Reference Boersma1998: 461ff, Mielke Reference Mielke2008, Dresher Reference Dresher2014, Reference Dresher2018, Odden Reference Odden2022; see also Goudbeek et al. Reference Goudbeek, Smits, Culter, Swingley, Claire and Cohen2005).

5.2.3. Son primes are hard wired

Section 2 has concluded that unlike other segmental properties, sonority is phonologically meaningful. This describes the fact that the Son module is not arbitrary. Unlike what is observed for Place and Lar, the computation of Son primes upon lexicalization is lawful (hence at odds with (2b):its result, structSon, is the same in all languages. That is, its items and their properties as well as their arrangement are universal: the list of structSon items is the same in all languages (onset, nuclei, feet, etc.), their properties are shared across languages (onsets host consonants, nuclei host vowels, or high sonority items) and their arrangement is also the same everywhere (onsets occur to the left, not to the right of rhymes, etc.).Footnote ³⁵

The association of a Son prime with a phonetic correlate is also not arbitrary (against (2c)). As Clements (Reference Clements, Raimy and Cairns2009: 165ff) points out, there are no flip-flop systems where all items that are vowels phonetically-speaking would be interpreted as consonants in the cognitive system upon lexicalization, and thus associate to a C position, while all items that are phonetic consonants would become phonological vowels and therefore associate to a V position. This means that Son primes are extracted from the phonetic signal in a predictable way that is at least partly the same in all languages. Clements (Reference Clements, Kingston and Beckmann1990: 291) says that “in the absence of a consistent, physical basis for characterizing sonority in language-independent terms, we are unable to explain the nearly identical nature of sonority constraints across languages” (see also Clements Reference Clements, Raimy and Cairns2009: 166).

There must thus be a way for humans to recognize the difference between consonants and vowels in the acoustic signal, and this capacity is put to use in such a way that there is a hard-wired relationship between a phonetic vowel and its lexicalization as a cognitive / phonological vowel, as well as between a phonetic consonant and its lexicalization as a cognitive / phonological consonant.

Therefore, children must roughly know what a vowel sounds like at birth, and in which way a vowel is distinct from a consonant. In an SFP setting, this means that they must have Son primes that are associated with a specific phonetic correlate. The literature has identified perceptual salience as a cross-linguistically robust correlate of sonority, which owes to phonetic properties such as loudness, energy and intensity (Bloch and Trager Reference Bloch and Trager1942: 22; Heffner Reference Heffner1950: 74; Fletcher Reference Fletcher1972: 82ff; Price Reference Price and J1980; Ohala Reference Ohala1992; Wright Reference Wright, Hayes, Steriade and Kirchner2004: 39ff; Harris Reference Harris2006; Clements Reference Clements, Raimy and Cairns2009; Parker Reference Parker2008, 2011; Gordon et al. Reference Gordon, Ghushchyan, McDonnell, Rosenblum, Shaw and Parker2012; Bakst and Katz Reference Bakst and Katz2014).Footnote ³⁶

Despite this massive literature, there are also voices saying that no phonetic correlate was ever identified: Hooper (Reference Hooper1976: 198), Ohala and Kawasaki (Reference Ohala and Kawasaki1984: 122), Ohala (Reference Ohala1990: 160),. Later on, though, Ohala (Reference Ohala1992: 325) arrives at about the same conclusion as the literature mentioned: sonority is the result of a number of acoustic parameters, that is, amplitude, periodicity, spectral shape and fundamental frequency.

The idea that no phonetic correlate of sonority is currently available may either lead to the rejection of sonority as an unscientific concept, or to consider the issue an open question whose answer is orthogonal to phonological analysis. The former position was taken by the early Ohala (Reference Ohala, Bruck, Fox and Galy1974: 252) who says that phonologists “invent meaningless labels for types of sounds and sound patterns (e.g., marked, strong, sonority, chromatic)” (on this, see Hankamer and Aissen Reference Hankamer, Aissen, Bruck, Fox and La Galy1974: 143, footnote 8).

The latter position is adopted by Hankamer and Aissen (Reference Hankamer, Aissen, Bruck, Fox and La Galy1974: 137), Hooper (Reference Hooper1976: 198) and Clements (Reference Clements, Kingston and Beckmann1990: 291): we know that sonority exists, since the analysis of phonological patterns shows it does, and there must be some phonetic correlate which, in the current state of our knowledge, we are not able to identify. Hooper (Reference Hooper1976: 198) argues that whether or not analysts are able to identify the phonetic correlate of sonority by machine measurements is irrelevant for linguistic analysis. We know that the human abstracts sonority from the acoustic signal, just as we know that the human is categorizing the gradient acoustic signal into discrete segments (or phonemes), while it is impossible to identify where exactly one segment ends and another begins, based on machine or other analysis of the signal. It would of course be enjoyable, Hooper says, to know how exactly the human extracts sonority and segments from the gradient acoustic signal, but our current ignorance is not an obstacle to taking sonority or the segment as a linguistic fact.

The situation described leaves no serious doubt that sonority does have a cross-linguistically stable phonetic correlate, and that this correlate is perceptual salience (in its various acoustic guises).

5.2.4. Sonority is phonetically composite and entropy-driven

The literature mentioned contains two ideas that are worth isolating. The observation that sonority is phonetically composite is made, among others, by Ohala (Reference Ohala1992: 325) and Harris (Reference Harris2006: 1486), the latter concluding “that sonority does not map to any unitary physical property but is rather a cover term for a collection of independent acoustic properties that contribute to an overall dimension of perceptibility or auditory-perceptual salience.” The other idea is that modulations (modifications of the signal) count, rather than static values (Ohala Reference Ohala1992: 325, Harris Reference Harris2006).

Stilp and Kluender's (Reference Stilp and Kluender2010) study is based on these two insights. It takes the latter idea to follow from Shannon's (Reference Shannon1948) more general information theory which is based on the idea that the degree of informativeness of an event depends on its entropy, that is, the uncertainty or unpredictability associated with it: the more unexpected, the more informative. Stilp and Kluender (Reference Stilp and Kluender2010: 12387) thus test “whether relative informativeness of portions of the speech signal is related to the degree to which the signal changes as a function of time.” On these grounds, they develop the notion of Cochlea-scaled Spectral Entropy (CSE), which “is a measure of the relative (un)predictability of signals that is operationalized as the extent to which successive spectral slices differ (or cannot be predicted) from preceding spectral slices. Most simply, CSE is quantified as Euclidean distances between equivalent-rectangular-bandwidth-scaled spectra of fixed-duration (16 ms) sentence slices that were processed by auditory filters” (p. 12388). They report that in their experiment “[t]his pattern of CSE decreasing from low vowels, to high vowels, to laterals/glides and nasals, to fricatives, to affricates, and finally stops closely parallels the sonority hierarchy” (p. 12389). They conclude that although in their measurements “there are no assumptions that the signal is created by a vocal tract” and “[w]ithout introduction of constructs such as distinctive features, CSE reveals distinctions between classes of speech sounds that mirror those in the sonority hierarchy. Although the present results are agnostic to linguistic constructs and theory, CSE could be construed as providing a case in which some linguistic distinctions are natural consequences of operating characteristics of the mammalian auditory system” (p. 12390).Footnote ³⁷

This is not to say that there is no slack, of course. It is not the case that all languages build the same sonority hierarchy based on the phonetic signal: in some languages, nasals count as (pattern with) sonorants, while in others they go along with stops. Only liquids may be second members of branching onsets in some languages, while in others nasals or glides also qualify for this position. In some languages, only vowels may be sonority peaks, while in others sonorants (or a subset thereof, typically liquids) may also occur in this position and act like vowels (syllabic consonants). The slack that is observed cross-linguistically for the specific location of a given phonetic item on the sonority hierarchy is called ‘relative sonority’. This variation has produced a massive body of literature (Clements Reference Clements, Kingston and Beckmann1990; Parker 2011, Reference Parker2017).

Note that the same workings allowing for some slack in a basic invariant frame are known from other cases, where a real-world continuum is converted into discrete cognitive categories. In colour perception, some distinctions like black and white have a physiological basis (magna vs. parvo layer cells of the lateral geniculate nucleus located in the thalamus, Kay et al. Reference Kay, Berlin, Maffi, Merrifield and Cook2009: 26) and may be selectively impacted by dysfunction: there are humans with no chromatic vision (achromatipsia, i.e., seeing only black and white). Beyond physiological grounding, the World Color Survey based on colour naming in 110 languages (Kay et al. Reference Kay, Berlin, Maffi, Merrifield and Cook2009: 25) has found that there are six universal sensations (four chromatic: red, yellow, green, blue and two achromatic: black and white) related to colour along which humans partition the colour space.

This partition follows some rules that appear to be universal, but allow for slack: languages may choose to follow a number of different partition paths. Thus, if a language has only two colour-terms, they will partition the spectrum into two chunks whose foci are black (or dark) and white (or light). They are never, say, green and yellow, or black and blue, etc. If there are three colour terms, the third will refer to red/yellow, and in cases where there are four words, the fourth will either split red into red/yellow and green/blue, or into red and yellow (green and blue being versions of black), or into red and yellow/green/blue. Languages with more colour terms also obey this kind of pattern, but the parametrical possibilities increase (Kay and McDaniel Reference Kay and McDaniel1978, Kay et al. Reference Kay, Berlin, Maffi, Merrifield and Cook2009).

Coming back to sonority, this suggests that the conversion of the phonetic signal into Son primes is partly shared by all humans, but allows for some slack that is conventionalized by each language. The work by Iris Berent supports the universal and innate character of sonority. Showing that sonority sequencing is ubiquitous in productive phonological processes, that it is supported by typological data and constrains the behaviour of speakers in psycholinguistic experiments, Berent (Reference Berent2013: 165ff) concludes that sonority sequencing is a grammatical universal since it cannot be derived from extra-grammatical factors (such as phonetics) (see also Berent et al. Reference Berent, Steriade, Lennertz and Vaknin2007). She further shows that sonority sequencing does not merely extend to lexical items that speakers have never come across: it is also active in structures that are unattested in the speaker's language, such as branching onset preferences produced by Korean speakers, whose language lacks branching onsets (Berent et al. Reference Berent, Lennertz, Jun, Moreno and Smolensky2008). Finally, as was mentioned in footnote 37, Berent et al. (Reference Berent, Dupuis and Brentari2013) adduce experimental evidence for sonority being in fact amodal, that is, a single system shared by the vocal and signed modalities whose expression is loudness etc. on the former, movement on the latter side.

5.2.5. Son primes do, Place and Lar primes do not come with a phonetic category

All representatives of SFP (see footnote 6) except those located at Concordia / Montreal hold that primes are emergent, that is, absent at birth, and that their association with phonetic categories is learned during first language acquisition (2c). The work done at Concordia rejects (2c), arguing that both primes and their association to phonetic categories are genetically coded and present at birth: there is a universal set of substance-free primes (α, β, γ) from which L1 learners choose when building their system, and which are associated to specific phonetic categories (Hale et al. Reference Hale, Kissock and Reiss2007: 647ff, Volenec and Reiss Reference Volenec and Reiss2018, Reiss and Volenec 2022).Footnote ³⁸

The former option is shown under (10a), the latter under (10b).

This distinction corresponds to the difference between the two types of primes discussed in the previous sections: while Place and Lar primes instantiate (10a), Son primes follow (10b).

5.4.1. Computational domains

In production, a computation is carried out in each module, based on the content of the lexical items (11b) that are retrieved from long-term memory, that is, the linearized string of morphemes that co-occur in a given computational domain (cycle, phase).

Upon production, computation thus takes structure (created upon lexicalization for each morpheme) as an input and returns (modified) structure. The difference between computation creating structure based on primes (lexicalization) and computation modifying existing structure (production) is reminiscent of the distinction that is made in syntax between internal Merge (creation of hierarchy based on primes) and external Merge (movement, i.e., the modification of existing structure).Footnote ⁴¹

In all cases, the domain of phonological computation is defined by the spell-out of morpho-syntactic structure which delineates specific chunks of the linear string that are called cycles or phases. It is obvious and consensual that these chunks are not defined in the phonology.Footnote ⁴²

5.4.2. StructSon

Computation modifying structSon includes all regular syllable-based processes, stress, as well as the communication with morpho-syntax: structSon (but not structPlace or structLar) and morpho-syntax do communicate, in both directions. Before proper phonological computation can run, though, the string of morphemes over which it operates must be pieced together and linearized.

Computation of structSon caused by linearization is shown under (12a). Morphemes need to be linearized, and this process may be conditioned by phonological information pertaining to Son (infixation (6a)). But items other than morphemes also need to be linearized: there is reason to believe that the exponent of stress may be syllabic space (depending on theoretical inclinations, an x-slot, an empty CV unit, a mora, etc.: Chierchia Reference Chierchia1986, Ségéral and Scheer Reference Ségéral, Scheer, de Carvalho, Scheer and Ségéral2008b, Bucci Reference Bucci2013). This extra space thus needs to be inserted to the left or right of the tonic vowel once the location of stress (ictus) is determined. This implies a modification of the linear order present in the lexicon.

The same goes for approaches where the carrier of morpho-syntactic information in phonology is syllabic space: in Strict CV the beginning of the word (or phase) incarnates as a CV unit (the initial CV; see Lowenstamm Reference Lowenstamm1999; Scheer Reference Scheer2012a, Reference Scheer, Bendjaballah, Faust, Lahrouchi and Lampitelli2014a). Note that there are no cases on record where the exponent of morpho-syntactic information is reported to be a Place or a Lar item inserted into structPlace or structLar (such as a labial or a voicing prime at the beginning of the word; see Scheer Reference Scheer2011: Section 663).

In the reverse direction, bearing of structSon on morpho-syntactic computation is documented for the items mentioned under (12b). Again, there are no cases on record where Place, Lar, structPlace or structLar would influence morpho-syntax. That is, morpho-syntax communicates with structSon in both directions, but is completely incommunicado with Place or structPlace, Lar or structLar (Scheer Reference Scheer2012a: Section126, see footnote 27).

Finally, cases of regular phonological computation involving structSon are shown under (12c).

5.4.3. structPlace and structLar

There is also a computation concerning Place primes and structPlace, such as palatalization, vowel harmony etc.: the prime associated to palatality is absent in velar but present in palatal segments, and a palatal source may add palatality to velars (front vowel harmony in V-to-V interaction, palatalization in V-to-C interaction). There is no need for going into more detail regarding Place and Lar: relevant phenomena are well known and not any different in the present environment from what they are in regular autosegmental structure: spreading, linking and delinking of primes.

5.4.4. Timing units are specified for consonant- and vowelhood

As is obvious in general and from the preceding, Place computation is informed of whether the items computed belong to a consonant or a vowel: vowel harmony is only among vowels, and in regular palatalization the trigger is a vowel and the target, a consonant. Information about vowel- and consonanthood is absent from the Place system, though. It must therefore be present in the only other structure that Place has access to: the timing units that represent linearity.

That Place has access to consonant- and vowelhood is also shown by a fundamental insight of autosegmentalism: the same primes may produce different segments depending on whether they are associated to consonantal or vocalic slots. High vowels and corresponding glides i-j, u-w, y-ɥ are the same segmental items and distinct only through their affiliation to a consonantal or a vocalic slot (Kaye and Lowenstamm Reference Kaye and Lowenstamm1984). For instance, when an i spreads its segmental content to a vacant consonantal position, it is interpreted as j: French li-er “to link” is pronounced [li-j-e], but the j is absent from both the root (il lie [li] “he links”) and the infinitive suffix (parl-er [paʁl-e] “to talk”). The same goes for lou-er “to rent” [lu-w-e] and tu-er “to kill” [ty-ɥ-e]: in all cases the glide is a copy of the preceding vowel into a C-position. This is shown under (13) where the Element I represents the Place specification of i/j (in substance-laden guise).

The idea that timing units are specified for consonant- and vowelhood goes back to Clements and Keyser (Reference Clements and Keyser1983).

5.5.1. Multiple-module spell-out

The existence of several computational systems (Son, Place and Lar) that concur in the pronunciation of a single segment raises a non-trivial challenge for the spell-out mechanism at the phonology–phonetics interface. Note that the situation is quite different from what we know from the morpho-syntax–phonology interface where the input to spell-out comes from one single system (morpho-syntax) and hence conveys one single vocabulary.

At the phonology–phonetics interface, Son, Place and Lar do not see each other and cannot communicate, but are segment-bound, that is, they must co-define the same segment. Therefore, segment integrity can only exist if the items of the three computational systems are related through a fourth player that defines the segment: the skeleton. Timing units that embody the linear structure of the string do precisely the job that is needed, that is, the definition of what does and does not belong to a segment. The difference between the upper spell-out that receives information from one single module and the lower spell-out which needs to combine inputs from three different modules is thus reflected by the presence of linearity in the latter, against its absence in the former. It is only the existence of linearity and hence the skeleton that affords the existence of a multiple-module spell-out.

It follows that the lower interface does not spell out individual primes or the set of primes defined by each one of the three computational systems, but entire segments as defined by timing units. How exactly timing units relate to segments is discussed in the following section.

5.5.2. Segment-defining root nodes are spelt out

Regular autosegmental representations allow for the association of a set of primes to multiple timing units as under (14a) where a geminate is shown. It is obvious that the primes must “know” whether they are associated to one or two timing units: this makes the difference between a short and a long item.

Let us consider the spell-out algorithm, that is, the way units are defined that are submitted to phonetic conversion. Spell-out cannot proceed timing unit by timing unit (Cs and Vs under (14)) since this would create two identical phonetic items under (14a): the association of α, β to a C would be spelt out twice, for the two Cs of the geminate. What is realized, though, is not two times the consonant in question, but the consonant with a longer duration (or with other phonetic correlates; see (19) below).Footnote ⁴³

Spell-out cannot proceed prime by prime either, since in this case α of the geminate under (14a) will be converted into a phonetic item, followed by the conversion of β, effecting, on the phonetic side, a sequence of items. In this case the phonetics would not “know” that the representatives of α and β need to be pronounced simultaneously, rather than in sequence.

It thus appears that the representation under (14a) is not suited to identifying the geminate segment at hand, that is, “α and β associated to two consonantal timing units”: there is no single item that encompasses this set. In traditional Feature Geometry (Clements and Hume Reference Clements, Hume and Goldsmith1995), the segmental unit is defined by the root node. This option is shown under (14b) where “R” is the root node.Footnote ⁴⁴ If the segment is defined by this item, spell-out may proceed root node by root node: for every root node present on the phonological side, a spell-out instruction is searched that contains all items affiliated. That is, the geminate under (14b) will be able to be spelt out by the spell-out instruction under (14c) (phonetic categories appear as ERB values; see section 5.6.2): spell-out will transmit the phonetic correlates of the primes contained in the root node (α, β), as well as the phonetic correlate (duration) corresponding to the fact that the root node is attached to two timing units (length).

This means that languages possess exactly as many spell-out instructions as there are phonemes (segments), that is, objects that are phonologically distinct. In comparison to the upper interface of morpho-syntax and phonology, the number of lexical entries whose content is inserted into the receiving module is thus very small: thousands of morphemes against 15 or 20, in very large inventories maybe 40 phonemes (segments).

5.5.3. Workings

When phonological computation (in all three modules) is completed, the result is spelled out root node by root node (i.e., segment by segment): root nodes are associated to Son, Place and Lar primes, which in turn are associated to their respective structure (see (11)). Spell-out considers only timing units and primes (Son, Place, Lar) associated to a given root node. The structure projected by primes (structSon, structPlace, structLar) is not taken into account. The restriction of spell-out to timing units and primes is motivated in section 6 below.

Spell-out matches the output of phonological computation with the phonological side of spell-out instructions, a lexicon where (language-specific and hence acquired) correspondences between phonological and phonetic categories are defined. For example, the spell-out lexicon entry under (15a) associates the Place prime α and the Son prime b, both belonging to a root node “R” and linked to a V slot, with the phonetic value “high front unrounded vowel” (or rather, the corresponding ERB value; see section 5.6.2). This assures the spell-out of the leftmost V of French li-er [lije] “to link” under (13b). By contrast, the second C under (13b) will match the spell-out entry (15b) where the same primes α (Place) and b (Son) are associated to a C position, a configuration whose phonetic correspondence is a high front unrounded glide.

5.5.4. Spell-out mismatches

Spell-out is a list-based mapping of one vocabulary set onto another. Therefore, the relationship between the two items matched is necessarily arbitrary (2c). The overwhelming majority of mappings appears to be “natural”, that is, phonetically reasonable, though: an item that shows the phonological behaviour of a labial is also realized as a phonetic labial. The overwhelming naturalness of mappings is due to the fact that phonological categories come into being when a phonetic item or event is phonologized. At birth, phonology is thus phonetically transparent and natural, with a faithful mapping. It takes some accident in the further life of phonological processes for them to become crazy, or for phonological items to develop a non-faithful mapping (Bach and Harms Reference Bach, Harms, Stockwell and Macaulay1972, Scheer Reference Scheer, Cyran and Szpyra-Kozlowska2014b: 268ff, Chabot Reference Chabot2019). That is, processes are not born crazy and mappings are not born unfaithful – they may become crazy and unfaithful through aging. This is one aspect of the life-cycle of phonological processes (Baudoin de Courtenay Reference de Courtenay and Niecisław1895, Vennemann Reference Vennemann, Stockwell and Macaulay1972, Bermúdez-Otero Reference Bermúdez-Otero and Lacy2007, Reference Bermúdez-Otero, Honeybone and Salmons2015).

Nonetheless, nothing in the system enforces or favours faithful mappings: “naturalness” and faithfulness are imposed by workings that lie outside both phonology and spell-out (third factor in the sense of Chomsky Reference Chomsky2005; see Chabot Reference Chabot2021). Spell-out is happy to accommodate any type of mapping, faithful or arbitrary. The ability of the system to lexicalize arbitrary mappings should thus have some empirical echo: at least some phonology–phonetics mismatches should exist. The cases mentioned under (16)–(19) show that this is indeed the case for all components discussed: Son under (16), Place under (17), Lar under (18) and timing units under (19). Note that the phenomena mentioned for the sake of illustration are only a small subset of the empirical record: phonology–phonetics mismatches are pervasive cross-linguistically (Hamann Reference Hamann, Kula, Botma and Nasukawa2011, Reference Hamann2014).

5.6.1. Language-specific phonetics

There is reason to believe that phonetics falls into two distinct computations: one that is language-specific, acquired during L1 acquisition and cognitive in kind (Language-Specific Phonetics, LSP), the other being universal and located outside of the cognitive system (Universal Phonetics). While LSP is acoustic in kind and defines language-specific gradient properties that identify a specific dialect or pronunciation (e.g., t being dental, alveolar, post-alveolar etc.), Universal Phonetics is shared by all languages: it is articulatory in kind and based on coarticulation, aerodynamics and other physical / physiological properties.

Unlike phonology which manipulates discrete objects, both phonetic systems are gradient in kind. LSP thus identifies as a cognitive system which is part of the grammar that speakers acquire, and like other grammatical systems (phonology, syntax) affords well-formedness: phonetic items may be well- or ill-formed (this is expressed by articulatory constraints in BiPhon; see Boersma and Hamann Reference Boersma and Hamann2008: 227ff). Kingston (Reference Kingston, Katz and Assmann2019: 389) says that “speakers and listeners have learned a phonetic grammar along with their phonological grammar in the course of acquiring competence in their language” (emphasis in original).

Evidence for LSP comes from the fact that “speakers’ phonetic behaviour cannot be entirely predicted by the physical and physiological constraints on articulations and on the transduction of those articulations into the acoustic properties of the speech signal” (Kingston Reference Kingston, Katz and Assmann2019: 389). A classical case is vowel duration, which is variable according to the voicing of the following consonant: voiced articulations (both sonorants and voiced obstruents) provoke longer durations to their left than voiceless obstruents. This appears to be (near) universal (Chen Reference Chen1970), but the ratios of long and short vowels are quite different across languages: Cohn (Reference Cohn1998: 26) reports that while vowels before voiceless consonants are 79% of the length of vowels before voiced consonants in English, in Polish the ratio is 99%, with other languages coming in between these values. This suggests that some phonetic properties are under the control of the speaker and depend on the language they have acquired.

Relevant literature describing the properties and workings of LSP includes Keating (Reference Keating and Fromkin1985), Pierrehumbert and Beckman (Reference Pierrehumbert and Beckman1988), Cohn (Reference Cohn1998), Cho and Ladefoged (Reference Cho and Ladefoged1999), Boersma et al. (Reference Boersma, Escudero, Hayes, Sole, Recasens and Romero2003); Cho (Reference Cho, Botma, Kula and Nasukawa2011: 343-346), and Kingston (Reference Kingston, Katz and Assmann2019) provide overviews.

5.6.2. Phonetic categories

If a spell-out hands over the output of phonology to another computational system that is cognitive (and grammatical) in kind, LSP, the question arises: what does the domain-specific vocabulary look like in this system? In the BiPhon model, the auditory continuum is expressed as an auditory spectral mean along the ERB scale (Equivalent Rectangular Bandwidth) (Boersma and Hamann Reference Boersma and Hamann2008: 229).

That is, the spell-out from phonology to LSP associates a phonological and a phonetic category, for example s ↔ 20,1 ERB. This reads “s is realized with a spectral mean of 20,1 ERB” and in a substance-free environment the consonant is replaced by alphas and betas. The goal of LSP (Auditory Form in BiPhon) in production is to determine an acoustic target in form of an ERB value that is transmitted to Universal Phonetics (Articulatory Form in BiPhon). Since LSP is gradual, but a simple spell-out instruction such as s ↔ 20,1 ERB produces a discrete ERB value, the computation carried out in the LSP module creates relevant variation: given an invariable and discrete phonological s, LSP computation produces ERB values with slight variation around the input from the spell-out instruction. This is responsible for some of the phonetically variable realizations of s. Variation/gradience is thus introduced by both the variable acoustic target that LSP produces and transmits to Universal Phonetics and the undershoot/overshoot that this target is subject to in the physical implementation carried out by Universal Phonetics.

Note that the red line between the discrete and the gradual is thus crossed in LSP: the input to LSP is a discrete ERB value contained in each spell-out instruction (s ↔ 20,1 ERB etc.). The modular computation operates over this ERB value and produces a gradient output. In the BiPhon model, the generation of the gradient output is achieved by adding noise to the computation either in the guise of multiple, slightly varying ERB values for a given spell-out that undergo an OT computation (constraints such as *s ↔ 20,1 ERB, *s ↔ 20,2 ERB, *s ↔ 20,3 ERB etc., Boersma and Escudero Reference Boersma and Escudero2004, Boersma and Hamann Reference Boersma and Hamann2008: 233ff) or by having the computation done by an artificial neural network (Seinhorst et al. Reference Seinhorst, Boersma, Hamann, Calhoun, Escudero, abain and Warren2019).

5.6.3. Visibility of morpho-syntactic divisions

Since LSP is a grammar-internal computational system, like all other modules it computes specific stretches of the linear string that are defined in terms of morpho-syntactic divisions, (i.e., cycles or phases; see section 5.4.1).

The visibility of morpho-syntactic divisions for phonetic processes is a disputed issue: in a feed-forward implementation of modularity as argued for by Bermúdez-Otero and Trousdale (Reference Bermúdez-Otero, Trousdale, Nevalainen and Traugott2012), modules can only take into account information of the immediately preceding module. Since phonology intervenes between phonetics and morpho-syntax, this perspective predicts that morpho-syntactic information will never be taken into account by phonetic processes. In a diachronic perspective, on this count, it is only when phonetic processes have been phonologized that a morpho-syntactic conditioning may kick in.

In a regular modular architecture (see section 2.4.2), there is no reason to restrict the availability of morpho-syntactic divisions, though. Like all other modules, LSP necessarily applies to a given computational domain. It is unclear how a cognitive computational system could work at all in absence of a specified stretch of the linear string over which it operates: there is no computation in absence of a computational domain. Hence the chunks defined in the morpho-syntax are handed down to all subsequent computational systems until the verge of the cognitive system is reached: universal phonetics is not cognitive in kind, and hence unbound by computational domains.Footnote ⁴⁸

Starting with Lehiste (Reference Lehiste1960), there is a substantial literature documenting cases where morpho-syntactic divisions are taken into account by phonetic processes. A well-studied item is l-darkening in English (Giles and Moll Reference Giles and Moll1975, Lee-Kim et al. Reference Lee-Kim, Davidson and Hwang2013, Strycharczuk and Scobbie Reference Strycharczuk and Scobbie2016, Mackenzie et al. Reference Mackenzie, Olson, Clayards and Wagner2018), but there is debate as to whether the gradient darkening overlaps with a categorical phonological process (Bermúdez-Otero and Trousdale Reference Bermúdez-Otero, Trousdale, Nevalainen and Traugott2012, Turton Reference Turton2017). If this is the case, Bermúdez-Otero and Trousdale (Reference Bermúdez-Otero, Trousdale, Nevalainen and Traugott2012), who reject the visibility of morpho-syntactic information in phonetics, can argue that l-darkening is influenced by morpho-syntactic divisions not in the phonetics, but in its phonological incarnation.Footnote ⁴⁹

In order to get around this caveat, Strycharczuk and Scobbie (Reference Strycharczuk and Scobbie2016) have tested whether phonetic processes may be sensitive to morpho-syntactic divisions. They study fronting of the goose vowel [uu] (see (17) in section 5.5.4), an ongoing sound change in Southern British English that is reported to be inhibited by a following coda l as in fool. The authors have experimentally contrasted fool with intervocalic l that is (fool-ing) or is not (hula) morpheme-final. Their results show that fronting is more inhibited in the former than in the latter case, thus documenting the impact of the morphological boundary. They carefully argue that the process at hand is gradient, rather than categorical, and therefore not a case of phonologically controlled allomorphy. They conclude that “morphological boundaries may affect phenomena that are phonetically continuous and gradient, and not only clear cases of allophony” (Strycharczuk and Scobbie Reference Strycharczuk and Scobbie2016: 90).