Sound Change in Functional Phonology

Sound systems may never stop changing, not even if only internal factors are present, because there may always be a better system. Non-teleological random variation of constraint ranking defines a pressure that explains the existence of perpetually rotating cycles of sound changes. In a companion paper (Boersma 1997b), I showed that the symmetries in inventories of sounds can be described and explained by general properties of motor learning and perceptual categorization, and that the gaps in these inventories can be described and explained by asymmetries in articulatory effort or perceptual confusion probabilities. Intimately related with the problem of inventories is the problem of sound change. After all, the inventories have been created in a long series of sound changes, and if inventories seem constructed according to functional principles, these same functional principles must be the driving forces for many sound changes as well. However, speakers cannot be expected to be able to see ahead to the state that their language will be in after the change: their goal is not to improve the language, but to make themselves understood as quickly, clearly, and easily as possible (Passy 1890). Thus, we have three levels of looking at sound change: (1) The grammar. In Functional Phonology (Boersma 1997a), the production grammar (i.e., the system that determines the shape of the utterance, given an underlying form) contains constraints that express the drives of maximizing articulatory ease and minimizing perceptual confusion either directly (by disfavouring gestures and favouring faithfulness) or indirectly (by their relative rankings). Strong evidence for the presence of these principles in the production grammar, which handles discrete phonology as well as phonetic implementation, is found in pragmatically based reranking of faithfulness: people are capable of speaking more clearly if they are required to do so. At this level, therefore, goal-oriented processes play a role; in Passy’s (1890, p.229) words, “one speaks in order to be understood”. For instance, if a language has a voicing contrast in /b/ and /p/, and underlying ñbñ and ñpñ are usually pronounced as [b] and [p], a speaker may enhance the contrast by implementing ñpñ as [pH], [p'], or [p ̆], thus reducing the probability that the listener will perceive the intended ñpñ as /b/, or by implementing ñbñ as [B], [∫], or [mb]. Paul Boersma Sound change in Functional Phonology 2 (2) The change. If many speakers let a certain constraint prevail, e.g., if many speakers implement ñpñ as [pH], new learners will include the aspiration in their specifications, thus creating a new underlying segment (= bundle of perceptual features) ñpHñ. This change is automatic; it was not a goal of anyone at any time. Though change, therefore, is not teleological (there is no final causation), it is functional in the sense that it is the result of local optimization in the production grammar. (3) The inventory. As a result of the change, the inventory has improved: a voicing contrast has changed into a voicing-and-aspiration contrast, reducing the average number of confusions. At this level, we can talk in teleological terms again, if only we know what we are doing. This is completely analogous to the common use of teleological jargon in discussions on biological evolution (“why giraffes have long necks”), where everyone realizes that what appears to be a historical gene change is the automatic result of the survival of the fittest (those with the longest necks) in the struggle for life (Darwin 1859), not the result of any goal. However, we saw above that in contrast with genetic change, whose ultimate sources are random mutations, the ultimate sources of (several types of) sound change are directly related to communicative principles in phonetic implementation. In order not to confuse the concrete (1) and abstract (3) uses of teleological terminology, we should refrain from describing change as goal-oriented at the inventory level. Thus we expect the following types of changes to be frequent: – Shifts with conservation of symmetry. The clearest examples can be read off from small regional variations. Dutch /e ̆/ is diphthongized to /ei/ in exactly the same regions where /o ̆/ is diphthongized to /ou/. This may reflect pure diachronic autosegmental behaviour of height contours (like we are used to in the case of tone contours), or result from a quick restoration of symmetry after an initial small imbalance. This restoration may take place as follows. If /e ̆/ slightly diphthongizes but /o ̆/ remains the same, listeners have to distinguish two very similar F1 contours. Quite probably, learners will put these two contours in the same perceptual category and subsequently see no reason to distinguish them in their own productions; the extra F1 contour has been temporary. – Filling of gaps. If (as the result of a blind sound change) an unnatural gap emerges in a system, subsequent sound changes or lexical selections will hurry to fill that gap. For instance, Latin inherited from Proto-Indo-European the stop system /p t k b d g/ with an unnaturally skewed distribution of voiced stops: though the implementation of voicing would be easiest for the labial plosive, only about 1.2% of all Latin words started with /b/, whereas /d/ accounted for 6% (without the deand di(s)words: 2%), and /g/ for 1.5% (as a page count in several dictionaries teaches us). In French, these numbers have become 5%, 6% (2%), and 3%. A weak interpretation of these facts is that the Proto-Indo-European gap at /b/ was in an unnatural position and that the local-ranking principle (Boersma 1997a: §11) caused Paul Boersma Sound change in Functional Phonology 3 this gap to be a lexical accident in the learner’s grammar, thereby allowing IndoEuropeans to freely borrow words with /b/ faithfully (Latin, Greek, Sanskrit) or to fill in the gap with a sound change (Greek: dw → b). A stronger interpretation of the same facts is that French borrowed /b/ to a larger extent than the other voiced plosives; this active de-skewing would presumably involve phonologically-determined choices between synonyms in the lexicon. Though I believe that these choices can be made in the production grammar (“choose the best candidate”), a proof of the controversial factuality of this procedure would require a large empirical investigation. Whether natural gaps, like the lacking /g/ in { p t k b d }, can also be filled, depends on the relative importance of the various factors involved, i.e. it depends on the rankings of the faithfulness, gestural, and categorization constraints (Boersma 1997b). – Emergence of new gaps. If a system obtains a phoneme at a location where it would be natural to have a gap, subsequent sound changes may create such a gap. Many of the defective stop systems /p t k b d/ used to have a /g/. A “passive” explanation would be that a learner does not hear the difference between /g/ and /k/ as well as the differences in the other pairs, and merges the two. An “active” explanation would be that speakers selectively modify their /g/ so that it becomes perceptually more distinct from /k/. In §1.2, I will show that these active modifications are actually used. The main idea to be learned from this small typology of functionally explainable sound changes, is that symmetrizing principles (“I have learnt a finite number of types of articulatory gestures and perceptual categories”) are just as “functional” as those depending on the biases of the human speech and hearing apparatuses (“minimize articulatory effort and perceptual confusion”). The functional tradition (Passy 1890, Martinet 1955) has always recognized that these principles conflict with each other and that every sound system shows a balance that is the result of a struggle between these principles. The important question, however, has always been: can and should these principles be expressed directly in a grammar of the language? In Boersma (1997a), I have shown that they can be represented in a production grammar, thanks to the formal constraint-based phonology of Optimality Theory (Prince & Smolensky 1993). In Boersma (1997a; to appear a; 1997b,c; to appear b,c), I argue that a phonological theory based on these principles adequately describes the data of the languages of the world without the need for positing any innate features, representations, or constraints. After elaborating on the controversy (§1), I will use the remainder of this paper to propose an answer to the irritating question: Q: “if functional principles optimize sound systems by causing sound change, why do not all languages get better, and why do languages never stop changing?” The proposed answer will simply be: “because there will always be a better system”. Paul Boersma Sound change in Functional Phonology 4 1 Criticisms of functionalism in sound change Several criticisms have been directed to the unclear definitions and lack of formalizability that used to go with the idea of functionalism. These criticisms come together in Trask’s (1996) definitions of both maximum ease of articulation and maximum perceptual separation as “somewhat ill-defined principle[s] sometimes invoked to account for phonological change”. With the gestural and faithfulness constraints of Functional Phonology (Boersma 1997a), however, the principles have received formal definitions that are capable not only of explaining, but also of describing sound patterns. Apart from the definitions of the principles, the concerted effects and interactions of the functional principles have also met with a poor press. Labov (1994) criticizes the simultaneous functional explanations of chain shift as an expression of the preservation of contrast and of parallel shift as an expression of rule generalization (i.e., preservation of symmetry): “the entire discussion will quickly become vacuous if we lump together explanations based on the facilitation of speech with those that are based on the preservation of meaning.” (Labov 1994, p. 551) However, we can use the constraint-ranking approach of Optimality Theory to combine many explanations without ‘lumping’; instead, they are interleaved, which makes all the difference. Several functional principles can play a role simultaneously. The existence of parallel chain shifts, by the way, proves that. 1.1 Ohala’s “phonetic” approach to sound change With the definition and formalizability issues out of the way, we can turn to another criticism, directed at the idea that functional explanations invoke goal-orientedness. Ohala (1993) aggressively argues against language change involving “goals”: “reliance on teleological accounts of sound change is poor scientific strategy. For the same reason that the mature sciences such as physics and chemistry do not explain their phenomena (any more) by saying ‘the gods willed it’, linguists would be advised not to have the ‘speaker’s will’ as the first explanation for language change”. (Ohala 1993, p. 263). Ohala’s own proposal involves synchronic unintended variation, hypo-correction, and hyper-correction. In his model, normal speech perception involves the process of correction, which occurs when a listener restores a phoneme from its contextually influenced realization. For instance, in a language with no contrasting nasality for vowels, the utterance [kA)n] can be reconstructed by the listener as the phoneme sequence ñkAnñ that was intended by the speaker, because she knows that every vowel is nasalized before a nasal consonant. Hypo-correction occurs if she fails to restore a phoneme, perhaps because the [n] was not pronounced very clearly, and analyses the utterance as ñkA)ñ. Paul Boersma Sound change in Functional Phonology 5 Hyper-correction refers to the listener restoring a phoneme from the troubled environment although it was not intended by the speaker. Ohala’s example is the Latin change /kwi ̆Nkwe/ ‘five’ → */ ki ̆Nkwe/. The first [w] in [kwi ̆Nkwe] may be interpreted by the listener as resulting from the spreading of the second, in which case it would be correct to reconstruct the word as ñki ̆Nkweñ. Ohala’s theory accounts for several attested sound changes; for instance, it explains most of Kawasaki’s (1982) data of a general avoidance of /wu/ sequences. However, his anti-teleological position denies the possibility of sound changes (or lexical choices) that seem to preserve the contrast between segments, like (to stay with the */wu/ example) the avoidance of /um/ insertion into /w/-initial stems in Tagalog. In the following section, I will discuss a case that probably does involve contrast enhancement. 1.2 The story of the fugitive /g/ Ohala (1993) maintains that languages change by misunderstanding of the input, and that goal-oriented drives are never at work. However, we will show in this section that speakers do try to solve the problems that arise when two sounds are hard to distinguish. We will do this by looking at an example that Ohala himself (Ohala & Riordan 1979) has noticed as a tendency in the languages of the world. Analogously to Ohala’s (1993) account described above, the relative voicelessness of [g], which is due to its short distance to the glottis, would result in misinterpretations of an intended /g/ as /k/. According to Ohala’s reasoning, the only thing /g/ could do, due to the small contrast with /k/, is to be misheard as /k/. If a language used to have [b]-[p] contrasts as well as [g]-[k] contrasts, and now still shows a [b]-[p] contrast but no [g][k] contrast, this would have to be due to a coalescence of the velar stops, in particular the conversion of /g/ into /k/. This would give a merger of /g/ and /k/ in all cases. Surely the /g/ could not travel away from this danger zone, which would be a bad case of teleology? Nevertheless, exactly this is what real languages seem to do: most languages that lost the /g/-/k/ contrast while retaining the /b/-/p/ contrast, did so by converting their /g/ into something perceptually more distinguishable from /k/. Here are a few examples. Arabic. In Arabic, an older /g/ was fronted and affricated, and became the palatoalveolar affricate /dZ/ (Moscati, Spitaler, Ullendorff & Von Soden 1964):