Allomorphy and stem classes

One function, several shapes

Allomorphs are different forms of a morpheme in different environments. Modern English plural [s] after the voiceless sound in books, [z] after the voiced sound in dogs, and [ɪz] after a sibilant in horses illustrate phonologically conditioned alternation. The written endings conceal some of the phonetic pattern. A learner must compare sound or a careful transcription, not only spelling.

A shape can instead be selected by lexical class. English child/children and ox/oxen show that one cannot predict every plural from the final sound alone. In historical languages, the grammar may organize stems into classes based on inherited endings, phonology or analogy. A class label is a summary of observed behavior; it should not substitute for a form-by-form citation.

Testing conditioning

Collect a set of stems taking each variant and ask whether a phonological property predicts the choice. If it does, formulate the environment and test it on further forms. If not, inspect stem classes and lexical exceptions. A single pair cannot establish whether the alternation is productive, restricted to a historical stratum, or merely orthographic.

Sound change can make an older regular alternation opaque. Conversely, analogy can level it within a paradigm. Separate a synchronic description of the attested period from an account of how the alternation arose. Both may be valuable, but they answer different questions.

Morphs and analysis

Do not force every surface piece to express one invariant meaning. A cumulative ending can be a single exponent for case and number, and a stem alternation can be part of the same paradigm. Record the surface form first, then the hypothesized morpheme and conditioning. If two analyses predict the same recorded forms, explain what additional evidence would distinguish them.

Practice

Using the English plurals cited above, predict the pronunciation of a new plural after a voiceless stop and after a sibilant. Then state why this modern prediction cannot be transferred to an ancient script without phonological evidence.