The linguist who has completed a phonemic analysis of a language ... is in about the position a chemist would be in when he had succeeded in isolating the elements. We have somewhat of an advantage over the chemist, for while he must keep a hundred and two elements, we have only 45 phonemes to worry about. But this doesn’t help us a great deal. The number of possible combinations of our 45 phonemes is for all practical purposes as great as the number of possible compounds of a hundred and two elements. There are so many, in fact, that only a small percentage of them are used in actual speech. Our next duty in studying the structure of English, therefore, is to see what combinations are used, and what they are like. The study of these matters is the province of morphemics. ...
... we know that the phonemes by themselves have no meaning. Therefore, we conclude that the meaning must somehow be associated with the way the phonemes are combined. ... Because these units have recognizable shape, we call them ‘morphs’, a name derived from the Greek word for ‘shape’ or ‘form’. A morph, then, is a combination of phones that has a meaning. Note that each morph, like each phone, or each person or each day, happens only once and then it is gone. Another very similar combination of very similar phones may come along right after it; if so, we will call this second combination another morph similar to the first one. If we are sure enough of the similarity, which must include similarity of both the phones and the
meaning, we can say that the two morphs belong to the same morph-type or allomorph. An allomorph can thus be defined as a family of morphs which are alike in 2 ways: (1) in the allophones of which they are composed, and (2) in the meaning which they have. Or if we wish to be a bit more precise, we can define an allomorph as a class of phonemically and semantically identical morphs. ...
We may sum up the material of this section, then, as follows: A morph is a meaningful group of phones which cannot be subdivided into smaller meaningful units.
An allomorph is a class of morphs which are phonemically and semantically identical; that is, they have the same phonemes in the same order and the same meaning.