Since what we test is the substitutability of segments, we cannot tell whether in a new utterance, e.g. 'Cash it!' the segment we record as [k⁽ʰ⁾] is equivalent to our previous [kʰ] segments until we have substituted one of these for it. It is true that after several attempts, we get to recognizing the differences among the various segments, so that even without making the test we can be quite sure, say, the [kʰ] of a newly recorded 'Can you?' Would be substitutable for the segments we have marked [kʰ].
- Harris (1951), Pag. 40