A fundamental observation of phonological theory is that, out of the rich sound signal of speech, a small subset of phonetic properties is contrastive in any given language. Standardly, this observation is captured by excluding the non-distinctive phonetic properties from some levels of representation, yielding an abstract categorical representation of the contrasts among the speech sounds. Universally non-contrastive features have generally been assumed to be unspecified throughout the phonological component; thus, for example, Keating (1984) and Lombardi (1991) have argued against inclusion of particular laryngeal features in phonological representation on the grounds that they are never contrastive. Language-particular non-contrastive features have generally been assumed to be unspecified only in underlying representation and early stages of the derivation (e.g. Kiparsky 1982, Archangeli 1984, 1988, Archangeli & Pulleyblank 1986, 1994, Steriade 1987, Clements 1988). Moreover, since the discovery of extensive language-particular gradient alternations, it has standardly been assumed that a subsequent phonetic component is needed, to fill in gradient and universally non-contrastive properties (e.g. Pierrehumbert 1980, Keating 1990; but see Pierrehumbert 1994 for an attack on this view of the phonetics–phonology interface). This model is schematised in Fig. 1.