Phonological alternations, processes and rules
The previous chapter was concerned with establishing the phonemic system which underlies the phonetic inventory of a language; that is deciding what the underlying set of contrasts is. Mention was also made (in Section 8.3) of the need to link the two levels formally via a set of rules which account for the particular allophone of a phoneme occurring in any speciﬁc environment. This chapter takes a closer look at this part of the phonological component of the grammar, starting with some discussion of the range of phenomena we have to account for as phonologists, and moving on to a more formal explication of the conventions of rule writing.
9.1 Alternations vs. processes vs. rules Much of the focus of recent phonological thinking concerns the characterisation of predictable alternations between sounds found in natural languages. We’ve already seen many examples of these alternations, such as that between [p] and [ph] in English. Under speciﬁc conditions, there is an alternation between these phones: we get one, [p], and not the other, [ph], after [s], as in [spt], not *[spht]. That is, while at the underlying (phonemic) level there is only one element, /p/, there is an alternation in the representation of this element on the surface (phonetic) level between [p] and [ph], which is determined by the environment in which the phoneme occurs.