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The linguistics encyclopedia 228
A universal set of well-formedness conditions is proposed to determine the permissible
associations, as well as rules which operate on the tonal tier itself. In more recent work,
other phenomena, such as vowel harmony (Clements, 1976) and nasalization (e.g.
Hyman, 1982), have been given a similar treatment.
Metrical phonology began as an interpretation of the stress rules of the SPE
framework (see Liberman, 1975; Liberman and Prince, 1977), in which it was shown that
the various stress levels could be derived from a hierarchically ordered arrangement of
strong and weak nodes. Such a hierarchy results in a metrical grid from which the stress
levels of individual syllables can be read off, e.g.:
This theory, too, has been extended into other areas, such as syllable structure (Kahn,
1976), and even into tonal structure, which in some cases can be shown to involve
hierarchical organization.
In both autosegmental and metrical phonology, a much richer phonological structure is
postulated than that which underlies SPE, and this has been further developed so as to
give a range of suprasegmental units such as syllables, feet, etc. (see Selkirk, 1980) or
tiers such as tonal tier, nasalization tier, etc. The relationship and complementary
nature of these theories have also been considered (Leben, 1982), and other hybrid
theories have developed which combine features of both autosegmental and metrical
principles, e.g. CV-phonology (Clements and Keyser, 1983). Other theories of
generative phonology, e.g. lexical phonology (Mohanan, 1981), have also been
considerably influenced by these non-linear frameworks (see Kiparsky,
1982;Pulleyblank, 1986).
The phonological representations assumed in these theories are very different from
those of the SPE model, and there has been a shift of focus away from discussions of
such issues as abstractness or rule ordering, and the appropriate formalisms, towards an
exploration of the structural complexities of such representations. Nevertheless, many of
the original principles of generative phonology, such as the postulation of an abstract
underlying phonological structure related by rules to a phonetic representation, have not
been abandoned.
A.F.