Having recorded an utterance in terms of the segments we associate with it, we now record repetitions of the utterance in identical environment. We then say that each segment of one repetition is freely substitutable for (or a FREE VARIANT of) the corresponding segment of every other repetition. That is, if an utterance represented by segments 'A'' 'B'' 'C'' is a repetition of the utterance recorded as 'A' 'B' 'C' (where 'A'' is the first n %— e.g. the first third—of the length of 'A'' 'B'' 'C'' and 'A' is the first n % of the length of 'A' 'B' 'C', etc.) then 'A' = A', 'B' = B', 'C' = C'. If the segments are freely substitutable for each other they are descriptively equivalent, in that everything we henceforth say about one of them will be equally applicable to the others.
- Harris (1951), Pag. 29