The existence of regular and irregular forms in the past tense in English and many related languages has been a subject of enquiry and speculation over a long period. Why should there be irregular verbs? Why do not all verbs in English form the past tense by a single, simple, rule? It is also puzzling that irregular verbs are not wholly irregular; they can be formed into small groups which share a similar pattern of past tense formation. In a recent book [Words and Rules: The Ingredients of Language 2001] Steven Pinker has discussed the problem of irregular verbs in English. The account he favours is that regular forms of the past tense are constructed by following the [default] rule: add -ed. Irregular forms, however, have to be learnt individually and recalled from memory each time they are used; he refers to the [rather uncertain] evidence from brain scanning that regular and irregular forms are processed by different areas of the brain. He is unable to explain why there should be irregular verbs, why they have persisted over long stretches of time and why the individual irregular past tenses have the diverse forms that they do.

Relevance to the issue of the motor theory of language ? The theory is that the sound structures of words are related to their meanings via motor equivalence, that is, the motor articulation of the word can be demonstrated in the form of gesturally equivalent motor patterning. To examine the effect of regular and irregular formation of the past tense, graphic comparisons are made between the final equivalent gestural patterns for the present tense and the past tense of two regular verbs and a selection from the complete set of irregular verbs. The general conclusion from these comparisons is that for both regular and irregular verbs the effect is the same. The change in the sound structure of a verb from the present to the past tense results in a small redirection of the equivalent gesture, away from the central line to the side of the body. For both regularly and irregularly formed past tenses, the basic shape of the gesture is preserved whilst the sideways shift marks the completion or pastness of the action. If instead of the irregular past tense, an artificially regular past tense is created e.g. come com-ed, the shape of of the gesture is not preserved or is distorted. There is reason to hypothesise that the position change associated with the past tense is part of a larger system extending to the full set of tenses.

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