Each element may be said to occur over some SEGMENT of the utterance i.e. over a part of the linguistic representation of the time-extension of the utterance. A segment may be occupied by only one element (e.g. only an intonation in the English utterance which is written 'Mm.' ), or by two or more short elements and one or more elements occupying a long segment in which the segment in question is included (e.g. a phoneme, plus a component like Moroccan Arabic’ stretching over several phonemic segments, plus an intonation extending over the whole utterance).
- Harris (1951), a pag.14

The segment over which an element extends is in some cases called the DOMAIN or interval or length of the element […] .
- Harris (1951), a pag.15, n.15

We represent an utterance by a succession of segments which end at arbitrary points along its duration. We hear a (preferably brief) utterance, i.e. a stretch of sound, say English 'Sorry. Can’t do it.', and consider it as a succession of any number of smaller elements. Each of these segments may be described very roughly as the sum of particular coincident movements of speech organs (lip closing.), or as so many sound-wave crests of such and such form.
- Harris (1951), a pag.26

We make analogous segmentations of repetitions of the utterance. Having recorded an utterance in terms of the segments we associate with it, we now record repetitions of the utterance in identical environment. We then say that each segment of one repetiton is freely substitutable for (or a FREE VARIANT of ) the corresponding segment of every other repetiton. That is, if an utterance represented by segments 'A' B' C'' is a repetition of the utterance recorded as 'ABC' (where 'A' is the first third—of the length of 'A B C' and 'A' is the first n%—e.g. the first third—of the length of 'A' B' C'' and 'A' is the first n%— of the length of 'ABC', etc.) then 'A' = A', 'B' = B', 'C' = C'. If segments are freely substitutable for each other they are descriptively equivalent, in that everything we henceforth say about one of them will be equally applicable to the others.
- Harris (1951), a pag.29

The comparisons of utterances […] not only enable us to say that certain segments (which have proved to be not mutually substitutable ) are descriptively non-equivalent or distinct (i.e. unsubstitutable).
- Harris (1951), a pag.33

[…] the segments should be neither longer nor shorter than is necessary to differentiate phonemically distinct utterances, so that minimally different utterances will differ in only one of their segments.
- Harris (1951), a pag.42

The environments are themselves composed of segments; e.g. in a complete chart, the same segments appear both in the vertical segment axis and in the horizontal environment axis.Therefore, whenever a number of segments is grouped into one phoneme, we must find these segments in the environment list and replace them by that phoneme. E.g. when we group the segments [r] of 'cry' and [r] of 'try' into one phoneme /r/, we must change the two environments [#—r] and [#—r] into a single (phonemic) environment /#—r/, since [r] is now identified with [r]. When we have done this, we can no longer group [t] and [k] into one phoneme, since they now contrast in /#—r/: both [t] and [k] occur before /r/. This prevents us from using a single restriction ([t] only before [r], [k] only before [r]) twice: e.g. from grouping [t] and [k] into one phoneme because they are complementary before [r] as against [r] (assuming that they do not contrast elsewhere), and at the same time grouping [r] and [r] into one phoneme because they are complementary after [t] as against [k].
- Harris (1951), a pag.62

Since the segments are defined as identifying particular sound stretches or sound feature, and since the phonemes will be defined as groupings of segments, it is convenient to have the definitions of the various segments within a phoneme simply related to each other.
- Harris (1951), a pag.64

[…] in some cases we may be unable to group segments into phonemes […] because there are too many or too few distinct segments recognized in a given environments, or because two segments which we would like to group together happen to contrast.
- Harris (1951), a pag.90

Segment and components which are dependent on particular phonemes environment, i.e., whose limitations of distribution can be stated in terms of the presence, of other phonemes, do not have phonemic status.
- Harris (1951), a pag.116

Identifying each segment as a combination of unit-length components will not in general eliminate the limitations of occurrence of the segments.
- Harris (1951), a pag.144

[…] if two segments are alternants of each other in a particular morpheme, they should also alternate similarly (under the same conditions) in every other morpheme which has the same phonemic constitution over such stretches as are considered in the phonemics.
- Harris (1951), a pag.234

By itself, the phoneme mark indicates all the members included in that phoneme. But when the phoneme mark occurs in a particular phonemic environment, it indicates only the particular segment member which has been defined as occurring in that environment: in the sequence /#peyr/ 'pair' the /p/ phoneme indicates only the [pʰ] member of that phoneme. […] the segments indicated by a phoneme mark never contrast (occur) in any environment in which the phoneme occurs […].
- Harris (1951), a pag.151, n.1