[…] in any corpus of material, it is possible to identify every linguistic element solely in terms of non-zero stretches of speech. For that matter, any corpus could be described in terms of elements each of which represents only the addition (to the utterance in which it occurs) of some stretch of speech. In some cases, however, it is convenient to identify an element as representing an interchange of segments (i.e. the omission of one stretch of speech and the addition of another in its place […]), rather than a simple addition. In other cases, we may recognize just the omission of a stretch of speech as indicating a linguistic element […]. Even in the simpler situations, when we say that two stretches of speech contain an identical additive element, we may not wish to state what part of each stretch represents that element (e.g. the components of chapters 10 and 17); in such cases the linguistic element represents the difference between two segments (as F represents the difference between Hebrew 'hu' ‘he’ and 'hi' ‘she’). Finally, we may wish to set up a linguistic element to indicate the non-addition and non-omission of anything in a particular environment, i.e. to indicate a segment consisting of zero. All such elements are possible, in terms of our present methods, because they are all definable in terms of segments: they are all relations among segments.
- Harris (1951), Pag. 334