[…] a phoneme is defined not as a speech sound or allophone, but as a ‘range’ of speech sound which functions as a point of contrast in an interlocking network of contrasts. A pnoneme is defined not so much in terms of what it “is” or what it “sounds like”, as in terms of what it is not-what, within the same language, it differs from.
- Hockett (1958), a pag.134

A phoneme is defined, not as a sound produced in such- and such a manner, but as a point of reference in an interlocking network of contrasts.
- Hockett (1958), a pag.112

The phonemes of a language, then, are the elements which stands in contrast with each other in the phonological system of the language.
- Hockett (1958), a pag.26