3.4 Distinctive features and non-distinctive features

　 In Chapter 2, we discussed phonetic features and natural classes. We know that features distinguish sounds. In this chapter we have shown that phonemes distinguish meaning, but that allophones do not. It is then natural and logical that features that distinguish phonemes and those that distinguish allophones are different in value. Features that distinguish meaning are called distinctive features, and features that do not, non-distinctive features. In sip and zip, the two words are both distinguished by /s/ and /z/. The two sounds are both alveolar fricatives. The feature that makes the two distinctive is voicing. In final analysis, the two words are distinguished by one feature only.

　 Distinctive features in one language may be non-distinctive in another. For example, aspiration is a distinctive feature in Thai, as shown in the minimal pair [paa] and [phaa] mentioned in 3.3.4. In English aspiration is non-distinctive. It is a feature that distinguishes allophones, [ph] and [p], [th] and [t], [kh] and [k]. Non-distinctive features are predictable. They are rule-governed in speech. This will be discussed in the following section.