Defective distribution

Of course, if /h/ and /ŋ/ were entirely normal phonemes, we would not have got into the problematic situation of regarding them as potential realizations of the same phoneme in the first place. In the normal case, we would expect some realization of every phoneme in a language to appear in every possible environment: initially, medially, and finally in the word, and also before and after other consonants in clusters. There are, however, two types of exception to this sweeping generalization.

First, there are the phonotactic constraints of a language, which spell out which combinations of sounds are possible. In English, only rather few three-consonant clusters are permissible; and the first consonant in the sequence must always be /s/. Nasal stops in English can cluster only with oral stops sharing the same place of articulation (unless the oral stop marks the past tense, as in harmed); hence lamp, clamber, plant, land, rink, finger, but not *lamk, *lanp, *[laŋt]. Even more specifically, /v/ and /m/ cannot be the first member of any initial consonant cluster, although both can occur alone initially, medially and finally; and /h/ never clusters at all (although, again, this was possible in Old English, where there are forms like hring ‘ring’, hwæl ‘whale’). Phonotactic statements of this kind restrict the length and composition of possible clusters, on a languagespecific (and period-specific) basis

Secondly, some phonemes have defective distributions: they are not only restricted in the combinations of consonants they can form, but are simply absent from some positions in the word. English /h/ and /ŋ/ both fall into this category, since the former is available only syllable-initially, and the latter only syllable-finally. It is because those defective distributions are mutually exclusive that English [h] and [ŋ] are in complementary distribution.

Phonemes with defective distributions like this are relatively rare. Sometimes, their defectiveness follows from their historical development: [ŋ] is derived historically from a sequence of [nk] or [ng ] where the nasal assimilated to the place of articulation of the following consonant; and since initial clusters of nasal plus stop are not permissible in earlier English or today, the appropriate context for [ŋ] never arose word-initially. Similarly, a chain of sound changes leading to the weakening and loss of /h/ before consonants and word-finally has left it ‘stranded’ only syllable-initially before a vowel; and there is a parallel story in non-rhotic varieties of English, where /r/ is pronounced before a vowel, but not before a consonant or a pause, meaning that [ɹ] appears in red, bread, very, but not in dark, car. Often, defectively distributed phonemes are relatively new arrivals. For instance, the newest member of the English consonant system is probably, which developed in Middle and Early Modern English from sequences of [zj] in measure, treasure, and from French loans such as rouge, beige: the [zj] sequence does not appear word-initially, and although French does allowhere, as in jamais ‘never’, no words with that structure have been borrowed into English, leading to an apparent prohibition on word-initial Englishwhich is really accidental, and may change in time (as suggested by recent loans like gîte).