Autosegmental phonology

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). According to 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 tonal 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 derivation of words from consonantal roots in Arabic could be analyzed autosegmentally.

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).

Structure of autosegmental rules

The autosegmental formalism departs from the depiction of segments as matrices of features in order to show segments as connected groups of individual features. Segments are depicted through vertical listings of features connected by lines. These sets can also underspecify in order to indicate a class rather than a single segment. Environments can be shown by placing other connected sets of features around that which is the focus of the rule. Feature changes are shown by striking through the lines that connect a feature that is lost to the rest of the segment and drawing dotted lines to features that are gained.

Distinctive features

Rather than classify segments using the categories given in the International Phonetic Alphabet, the autosegmental formalism makes use of distinctive features, which provide greater granularity and make identification of natural classes easier. A segment is identified by a +/− dichotomy of a series of binary features, some of which are subfeatures of unary features (place of articulation, in particular, is identified by unary features indicating the active articulator, and binary subfeatures that distinguish further). For example, [p], the voiceless bilabial stop, is indicated [−sonorant, −continuant, −voice, labial], and the set of voiced coronal stops can be indicated [−sonorant, −continuant, +voice, coronal].

Feature dependencies

For unary features to be fully specified, it is necessary to include binary subfeatures that correspond to them. In the autosegmental formalism, this is depicted by placing the binary subfeature at a horizontal offset from the unary feature and connecting them with a line. The next top-level feature in the segment would then be connected to the unary feature as well as opposed to the tone.

Functional groupings

There are situations in which the rule applies not to a particular value of a feature, but to whatever value the feature has. In these situations, it is necessary to include the presence of the feature, but not to specify its value. This can be done by including a placeholder feature composed of ellipses, with an indication of the type of feature. For example, a generic place feature can be indicated [...]_P.