Goldsmith’s Autosegmental Phonology has two layers: at the first level it merely accepts the SEP invitation to consider matters of tone which were completely avoided by Chomsky and Halle, but at the second it offers a potentially radical revision in the systematic phonetic one ,which are conceived in SPE as single-stranded concatenation of segments each of which consists of a cluster of simultaneous features. Goldsmith at least envisages the possibility of several parallel concatenations with variable linkages (“association lines”) between segments in one and segments another.
Again no fundamental axioms of SPE are altered. The proposal suggests various testable speculations about language acquisition by children and eases the formalization of various changes, particularly assimilations, some of them also improvable by theories such as R.Cheng’s（1977）,which make the sequence single but the units in it syllables, each syllable being a bundle of simultaneous features which may be arranged in various ways on the surface. Many of the same goals may be attained either by multiplying the strings vertically or broadening the beads horizontally.
In recent years a great deal of work has gone into the description of prosodic processes in language, and two advances that have come out of this work are the frameworks of autosegmental phonology and metrical phonology. These two frameworks provide ways of escaping the assumption, which used to be quite ordinary in phonological theory, that speech and phonological representation could both be represented linguistically as nonlinear sequences of discrete symbols. This development seems particularly fortunate, since the approaches in question appear to express some of the prosodic properties of speech much more adequately and elegantly than previous ones. However, for a given prosodic phenomenon in language, it is not always easy to determine which sort of analysis-metrical or autosegmental-will be the most appropriate. Halle (1980) is the first attempt to deal with this problem, though almost totally in the area of vowel harmony. The present paper will attempt to deal with this question in a somewhat more general way.
Autosegmental phonology A term used in recent PHONOLOGICAL theory to refer to an approach which contrasts with strictly SEGMENTAL theories of phonology. The segmental approach is seen as a set of REPRESENTATIONS which consist of a LINEAR arrangement of segments (of unordered sets of FEATURES) and BOUNDARIES that are dependent on MORPHOLOGICAL and SYNTACTIC criteria. By contrast, the autosegmental approach sees phonology as comprising several TIERS, each tier consisting of a linear arrangement of segments; these are linked to each other by association lines which indicate how they are to be COARTICULATED. Originally devised to handle TONAL phenomena, the approach has now been extended to deal with other features whose scope is more than one segment, especially VOWEL and CONSONANT HARMONY.
At the bottom layer (L1), or row, each TERMINAL NODE of the TREE is aligned with a grid placeholder (marked by x); this layer is the grid’s ‘terminal seet’. A second layer is used to reflect the relative strength of teen and men, as opposed to third; and a third layer is used to reflect the relative strength of men as opposed to teen. Grid elements at the same layer are said to be ‘adjacent’ Adjacent elements are ‘alternating’ if, at the next lower layer, the elements corresponding to them (if any) are not adjacent (as in the antique settee example); they are ‘clashing’ if their counterparts one layer down are adjacent (as in the thirteen man example). The relationship between trees and grids proved controversial; some phonologists argued that the formalisms are equivalent, and that only grids need be represented (an ‘autonomous’ grid, ‘grid-only’ phonology); some argued that only trees need be represented (‘tree-only’ phonology); and some argued that both are required because they have different functions (trees representing STRESS, grids representing RHYTHM). Grid construction is carried out using a set of PARAMETERS (e.g. QUANTITY SENSITIVITY). The rhythmical basis of the grid is provided by the rule of perfect grid: a foot layer mark is added on top of alternating syllable-layer marks. Bracketed grid theory is a metrical grid with CONSTITUENCY markers added, introduced to formalize a constituent structure view of rhythm. Various notations have been proposed.
Metrical phonology A theory of PHONOLOGY in which phonological STRINGS are REPRESENTED in a HIERARCHICAL manner, using such notions as SEGMENT, SYLLABLE, FOOT and WORD (of also PROSODIC phonology). Originally introduced as a hierarchical theory of STRESS, the approach now covers the whole domain of syllable structure and phonological boundaries. Stress patterns are considered to reflect, at least in part, relations of PROMINENCE between SYNTACTIC and MORPHOLOGICAL CONSTITUENTS. The UNDERLYING metrical STRUCTURE of words
and PHRASES may be represented in the form of a metrical TREE, whose NODES reflect the relative metrical strength between SISTER , constituents, as in the following examples (W = weak, S = strong):