As a theory of phonological representation, autosegmental phonology developed a formal account of ideas that had been sketched in earlier work by several linguists, notably Bernard Bloch (1948), Charles Hockett (1955) and J. R. Firth (1948). On such a view, phonological representations consist of more than one linear sequence of segments; each linear sequence constitutes a separate tier. The co-registration of elements (or autosegments) on one tier with those on another is represented by association lines. There is a close relationship between analysis of segments into distinctive features and an autosegmental analysis; each feature in a language appears on exactly one tier. The working hypothesis of autosegmental analysis is that a large part of phonological generalizations can be interpreted as a restructuring or reorganization of the autosegments in a representation. Clear examples of the usefulness of autosegmental analysis came in early work from the detailed study of African tone languages, as well as the study of vowel and nasal harmony systems. A few years later, John McCarthy proposed an important development by showing that the vocalism and consonantism of Arabic could be analyzed autosegmentally.
As a theory of the dynamic of phonological representations, autosegmental phonology includes a Well-formedness Condition on association lines (each element on one tier that "may" be associated to an element on another tier "must" be associated to such an element, and association lines do not cross) plus an instruction as to what to do in case of a violation of the Well-formedness Condition: add or delete the minimum number of association lines in order to maximally satisfy it. Many of the most interesting predictions of the autosegmental model derive from the automatic effects of the Well-formedness Condition and their independence of language-particular rules.
In the first decade of the development of the theory, G. N. Clements developed a number of influential aspects of the theory involving harmonic processes, especially vowel harmony and nasal harmony, and John McCarthy generalized the theory to deal with the conjugational system of classical Arabic, on the basis of an autosegmental account of vowel and consonant slots on a central timing tier (see also nonconcatenative morphology).