It must be borne in mind that when we ask for repetitions we may get a totally different utterance (e.g. 'auto' for 'car'), or a partially different one ('rocking-chair' for 'rocker'). The different utterance may be sufficiently similar in sound to mislead us. If the putative repetitions come in different environments (e.g. 'knife', but 'knive' before '–s'), the present procedure does not enable us to equate the corresponding segments (we cannot say [f] = [v]).
- Harris (1951), a pag.37

Utterances or parts of them are considered equivalent to each other if they are repetitions of each other […].
- Harris (1951), a pag.361