Distinctive feature theory

Just saying that rules are defined in terms of phonetic properties is too broad a claim, since it says nothing about the phonetic properties that are relevant. Consider a hypothetical rule, stated in terms of phonetic properties:

all vowels change place of articulation so that the original difference in formant frequency between F1 and F3 is reduced to half what it originally was, when the vowel appears before a consonant whose duration ranges from 100 to 135 ms.

What renders this rule implausible (no language has one vaguely resembling it) is that it refers to specific numerical durations, and to the difference in frequency between the first and third formant.

An acoustic description considers just physical sound, but a perceptual description factors in the question of how the ear and brain process sound. The difference between 100 Hz and 125 Hz is acoustically the same as that between 5,100 Hz and 5,125 Hz. The two sets are perceptually very different, the former being perceived as “more separate” and the latter as virtually indistinguishable.

The phonetic properties which are the basis of phonological systems are general and somewhat abstract, such as voicing or rounding, and are largely the categories which we have informally been using already: they are not the same, as we will see. The hypothesis of distinctive feature theory is that there is a small set, around two dozen, of phonetically based properties which phonological analysis uses. These properties, the distinctive features, not only define the possible phonemes of human languages, but also define phonological rules.

The classical statement of features derives from Chomsky and Halle (1968). We will use an adapted set of these features, which takes into consideration refinements. Each feature can have one of two values, plus and minus, so for each speech sound, the segment either has the property (is [+Fi]) or lacks the property (is [-Fi]). In this section, we follow Chomsky and Halle (1968) and present the generally accepted articulatory correlates of the features, that is, what aspects of production the feature relates to. There are also acoustic and perceptual correlates of features, pertaining to what the segment sounds like, which are discussed by Jakobson, Fant, and Halle (1952) using a somewhat different system of features.