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Phonetics & Phonology 101: Phonological Opacity, a Debate in Modern Phonology


Phonetics and phonology are two essential parts of linguistic competence. While both are related to the processes of production and perception of language sounds, they differ in their approach and goals. Phonetics is concerned with the physical properties of sounds, i.e., articulatory, acoustic, and perceptual, and aims at a scientific description and classification of all sounds attested in human languages. Phonology, on the other hand, is more focused on how these sounds are organized in single languages, i.e., how they constitute their phonological inventory through distinctive oppositions and how they relate to morpho-syntax and semantics. This course aims at introducing the reader to both disciplines, focusing on the following aspects: (a) the basic concepts of phonetics and phonology, their interrelation, and differences; (b) the use of IPA to write phonetic and phonological transcriptions; (c) the major issues and debates in modern phonological theory.

This series is divided into the following chapters:

Phonetics & Phonology 101: Phonological Opacity, a Debate in Modern Phonology

In chapter four, two distinct approaches to the characterization of phonological competence have been exposed, namely the rule-based and the constraint-based approach. The constraint-based approach, which was developed within Optimality Theory, justifies the output forms in a way that is both adequate and (relatively) simple. In the 90s' some problems emerged within this theory. In particular, phonological opacity was seen as a kind of phenomenon which a constraint-based approach cannot explain satisfyingly.

Phonological Opacity

Green (2004, 37) has defined phonological opacity in the following terms:

Phonological opacity is the phenomenon of a process applying even though its environment is not present on the surface (overapplication), or of a process failing to apply even though its environment is present on the surface (underapplication).

Thus, opacity is the effect of specific rule orderings: the order by which rules apply may generate opaque forms in the output. A typical phenomenon of opacity is present in Hebrew. This language shows regular spirantization: non-emphatic stops alternate with fricatives in predictable contexts. Idsardi (1998, 47) formalizes this regularity with the following phonological rule: “a stop which is adjacent to a preceding syllabic nucleus is realized as a fricative in the output”. Consider the following forms, where spirantization applies regularly: ‘melekh’ (king) and ‘sefer’ (book). Here, underlying ‘k’ and ‘p’ (consider first person pronominal forms like ‘malk-ì’ and ‘sipr-ì’) surface as spirants ‘kh’ and ‘f’. Such a regularity seems missing in verbal forms like ‘kathvu’ (they write) and ‘ganvu’ (they steal), where the spirantization b --> v clearly violates the spirantization rule given by Idsardi. This is not really the case, i.e., the violation is only apparent. The reason why b --> v seems irregular is that this rule has been applied in an internal phase of the phonological derivation, where a vowel (in this case, ‘a’) was present and, after triggering the spirantization, has been deleted due to the application of a distinct rule of the language. The entire process is represented in Figure 1.

Figure1. Phonological derivations for Hebrew spirantized forms (Piersigilli, 2020).

Accounts based on classic OT cannot explain why the final forms are those attested, simply because such accounts are based on the notion of optimal forms, i.e., forms that surface because of the non-violation of the fatal constraints of the language. Paradoxically, forms like ‘kathvu’ and ‘ganvu’ would be eliminated by the phonological computation because of their clear surface-apparent violation of regular spirantization.

New Proposals within OT

While cases of phonological opacity across different languages convinced a part of the linguistic community that constraint-based models like OT were wrong and thus rule-based models inspired by SPE were preferable, many supporters of OT stated that such an incongruency was, in fact, fixable by modifying the original proposal. These new elaborations are mainly of two kinds: John J. McCarthy formulated the so-called “sympathy theory” (McCarthy, 1999), while Paul Kiparsky proposed a stratal model of OT. The main innovations and the two are presented in the following lines.

Chapter four has shown that the attested forms in OT are referred to as optimal candidates. Since opaque forms are not optimal at all, McCarthy introduced the notion of sympathetic candidates. The function of these candidates is to force the input forms to surface not in relation just to the optimal forms but also to these sympathetic forms. Such a process is shown in Figure 2, where the flower symbol indicates the sympathetic candidate and the first line contains various phonological constraints.

Figure 2. Tableau for 'deshe' (grass) under sympathy theory (Piersigilli, 2020).

A distinct approach is that which considers opacity as a feature of just some components of the language. Stratal OT has been theorized to explain this variability in the occurrence of opacity in the language taken into consideration. Opacity is not a problem for phonological theory and does not need to be explained through rule-ordering because it is strictly predictable according to the grammatical mechanisms. For example, Tiberian Hebrew shows regular opacity in verbal suffixation and in lexical prefixation, but not in verbal prefixation.

Such new approaches to opaque forms have been harshly criticized by Green, who stated, “Sympathy theory is an attempt to [allow] a fully parallel selection of both the sympathetic candidate and the optimal candidate, but it is unclear to what extent this is conceptually really possible. If the selection of the optimal candidate depends on faithfulness to the sympathetic candidate, then the selection of sympathetic candidate must happen in some sense 'before' the selection of the optimal candidate”. The presence of these internal layers, according to Green, introduces a derivational element that should not be present in a clearly anti-derivational approach like OT (both in its classic and ‘evolved’ form). With regards to stratal OT, he claimed, “Traditionally in lexical phonology each level corresponded to some level of morphological affixation. That is not always the case in opacity cases, rendering stratal OT analyses of opacity somewhat ad-hoc” (Green, 2004).

Opacity as an Analogical Phenomenon

Green himself, denying the validity of such innovations within OT, has considered opacity not to be a phonological problem at all. According to him, opacity is nothing but the effect of a grammatical phenomenon known as an analogy. So, there are recurring patterns in some grammatical classes. Such patterns are so frequent that they may become generalized to the entire grammatical class. Taking into account the case of Hebrew opacity, Green observes that: (a) the ‘irregular’ forms (opaque) in the imperative paradigm are due to the fact that most forms exhibit regular spirantization. Cases in which spirantization is irregular, or opaque, then, are just the adaptation of this form to the general pattern for imperatives; (b) nominal inflection too conforms to the general spirantization pattern (Figure 3).

Figure 3. Spirantization pattern for nominal forms 'kokhov' (star) and 'melek' (king) (Piersigilli, 2020).

After considering all these theoretical proposals, it is difficult to draw a conclusion on which approach is the most adequate to explain opacity. If it is true, as Green claims, that both stratal OT and sympathy theory are reducible to derivational phonology, then two alternatives stand: i) opacity shows derivational phonology to be better from an explanatory point of view or ii) opacity is not a problem at all; therefore OT maintains its virtues, namely being adequate and economical. Green explicitly chooses the second alternative: once he has shown TH opacity to be explainable in morphological terms (i.e., relying on the principle of general paradigm uniformity), he concludes that this is generally true for all the attested cases of opacity. This is not evident at all. Instead, it requires further investigation. Of course, one cannot dismiss Green’s hypothesis a priori, but it is clear that, at the present state, the burden of proving is on him and not on derivational models, which have shown their adequacy for all the cases of opacity attested.

Opacity as a Psycholinguistic Problem

The interesting fact about opacity is that it may be considered as a case of what Bertrand Russell called Plato’s problem: how do humans acquire knowledge of something which is not empirically evident? Indeed, opacity presupposes rule (or constraint) ordering which is never explicitly taught to children. They just seem to be able to draw generalizations relying on a limited amount of data.

Derivational models may interpret the acquisitional process in two different ways and only partially compatible with one another : (a) adults and children share the same underlying forms. The phonological systems, during language development, proceed to re-order, simplify or delete rules. For example, Smith (1973) has shown that English native-speaker children apply a rule which converts the initial /d/ into [g] in words like /dɔg/ à [gɔg] and /dʌk/ à [gʌk]; (b) the child associates the received forms in input to the underlying forms, and this thus makes the latter different from adults’ underlying forms. To facilitate production, children use simplifying rules which are then put aside during development and then they acquire adult-like underlying forms (Kiparsky and Menn, 1977).

According to optimal models, underlying forms for adults and children are the same. Constraints are innate and are the same for adults and children, but differences in their ordering may manifest during acquisition. Imperfect forms produced by children are the result of such differences. Thus, the acquisition is error-driven: “The detection of mismatches in children’s own productions and target forms will trigger changes in the grammar.” (Fikkert, 2007).

Other proposals, like distributional models, support the view that opacity may be acquired by simply relying on distributional evidence (Rasin, Berger, et al. 2018; Rasin and Katzir, 2018). According to this view, there is no Plato’s problem in phonological opacity.


The debate over opacity is still far from being concluded: the occurrence of phonological phenomena across many languages (Hebrew, Bulgarian, Dutch, English) has been representing a challenge for optimal models while reviving classical rule-based models. On the experimental side, there are no conclusive studies today about how opacity is effectively acquired. This article has shown some theoretical proposals and considered psycholinguistic evidence, showing how this debate is relevant in modern phonology. The next chapter will focus on a more general topic: the relationship between phonological competence and language acquisition.

Bibliographical References

Fikkert, P. (2007). “Acquiring phonology”. Handbook of phonological

theory, pp. 537–554.

Green, A. (2004). “Opacity in Tiberian Hebrew: Morphology, not

Phonology”. ZAS Papers in Linguistics 37, pp. 37–70.

Idsardi, W. (1998). “Tiberian Hebrew Spirantization and

Phonological Derivations”. Linguistic Inquiry 29.1, pp. 37–73.

McCarthy, J. J. (1999). “Sympathy and phonological opacity”. Phonology 16.3, pp. 331–399.

Kiparsky, P. (2000)."Opacity and cyclicity" , vol. 17, no. 2-4,pp. 351-366.

Kiparsky, P. and Menn, L. (1977). “On the acquisition of phonology”.

Language learning and thought. 47778.

Rasin, E., Berger, I. et al. (2018). “Learning phonological optionality

and opacity from distributional evidence”. Proceedings of NELS.

Vol. 48, pp. 269–282.

Rasin, E. and Katzir, R. (2018). “Learning abstract underlying

representations from distributional evidence”. Proceedings of NELS.

Vol. 48, pp. 283–290.

Smith, N. (1973). The Acquisition of Phonology: A Case Study.

Cambridge University Press.

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Federico Piersigilli

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