Autosegmentalmetrical

Autosegmental-Metrical theory, often abbreviated AM theory, is a framework for phonological representation that unites autosegmental phonology with metrical theory. It treats phonology as organized on multiple tiers, rather than a single linear string. In AM theory, certain features—such as tone, vowel length, nasalization, or phrasal prosody—are represented on separate autosegments or tiers. These autosegments can be linked to multiple segments via association lines, allowing a feature to be shared or spread across several segments without being bound to a single segment. This accounts for phenomena such as tone spreading, downstep, and tonal morphology without forcing a one-to-one segment-to-feature correspondence.

Alongside autosegments, AM theory uses a metrical tier to represent the hierarchical structure of prosody, including feet, syllables, and higher prosodic constituents. The metrical grid provides a way to model stress assignment, syllable weight, and prosodic prominence, with association lines linking segmental material to the appropriate positions in the metrical structure.

The framework was introduced in the 1970s by John Goldsmith and was developed into a full autosegmental-metrical theory by researchers in generative phonology. It has been influential for analyzing tone languages (where pitch is not strictly attached to segments) and for capturing interactions between tone, stress, and other prosodic phenomena in a unified representation.

Over time, AM theory has influenced subsequent approaches to phonology, though it faced critiques regarding complexity and the rise of alternative theories such as constraint-based or probabilistic models. It remains foundational in the study of non-linear phonology and prosodic structure.