[…] the distinct phonemic composition of each utterance is defined as the sum of its minimal differences from all other utterances of the language. For a pair such as 'pick-pit' we find no smaller minimal differences than the difference between these two members of the pair. The difference in the 'pick-pat' pair can be stated as the sum of the 'pick-pit' and and 'pit-pat' differences. The difference in 'sick-land' can be stated as the sum of the difference in, say, 'sick-sack', 'sack-lack', 'rack-ran', 'fine-find', each of these having been shown previously to be a minimal difference. We identify 'sick' by its difference, stated in this manner, from all other utterances of the language.
- Harris (1951), Pag. 43