The verb 'teach' originates from the Old English 'tǣcan', meaning to show, point out, or instruct. Its past tense form 'taught' derives from the Old English 'tǣhte', which was the first and third person singular past tense. This change from 'teach' to 'taught' represents a common Germanic pattern of strong verb conjugation through internal vowel alteration (ablaut), rather than by adding the regular '-ed' suffix. The specific vowel shift here is part of a pattern seen in other English verbs like 'catch/caught' and 'buy/bought'. Over time, 'taught' became standardized as the sole past form, losing its status as a regular strong verb and becoming an irregular form that must be memorized.

The word 'taught' is a suppletive form of the verb 'teach'. It is not productively formed from separable morphemes in Modern English. Its core is the Germanic root of 'teach', which underwent a vowel change (ablaut) to form its past tense and past participle.