The grammatical description of many, if not all, languages is conveniently divided into two complementary sections: morphology and syntax. The relationship between them, as generally stated, is as follows: morphology accounts for the internal structure of words, and syntax describes how words are combined to form phrases, clauses, and sentences.

There are many words in English that are fairly obviously analyzable into smaller grammatical units. For example, the word “unacceptability” can be divided into un-, accept, abil-, and -ity (abil- being a variant of -able). Of these, at least three are minimal grammatical units, in the sense that they cannot be analyzed into yet smaller grammatical units—un-, abil-, and ity. The status of accept, from this point of view, is somewhat uncertain. Given the existence of such forms as accede and accuse, on the one hand, and of except, exceed, and excuse, on the other, one might be inclined to analyze accept into ac- (which might subsequently be recognized as a variant of ad-) and -cept. The question is left open. Minimal grammatical units like un-, abil-, and -ity are what Bloomfield called morphemes; he defined them in terms of the “partial phonetic-semantic resemblance” holding within sets of words. For example, “unacceptable,” “untrue,” and “ungracious” are phonetically (or, phonologically) similar as far as the first syllable is concerned and are similar in meaning in that each of them is negative by contrast with a corresponding positive adjective (“acceptable,” “true,” “gracious”). This “partial phonetic-semantic resemblance” is accounted for by noting that the words in question contain the same morpheme (namely, un-) and that this morpheme has a certain phonological form and a certain meaning.

Bloomfield’s definition of the morpheme in terms of “partial phonetic-semantic resemblance” was considerably modified and, eventually, abandoned entirely by some of his followers. Whereas Bloomfield took the morpheme to be an actual segment of a word, others defined it as being a purely abstract unit, and the term morph was introduced to refer to the actual word segments. The distinction between morpheme and morph (which is, in certain respects, parallel to the distinction between phoneme and phone) may be explained by means of an example. If a morpheme in English is posited with the function of accounting for the grammatical difference between singular and plural nouns, it may be symbolized by enclosing the term plural within brace brackets. Now the morpheme [plural] is represented in a number of different ways. Most plural nouns in English differ from the corresponding singular forms in that they have an additional final segment. In the written forms of these words, it is either -s or -es (e.g., “cat” : “cats”; “dog” : “dogs”; “fish” : “fishes”). The word segments written -s or -es are morphs. So also is the word segment written -en in “oxen.” All these morphs represent the same morpheme. But there are other plural nouns in English that differ from the corresponding singular forms in other ways (e.g., “mouse” : “mice”; “criterion” : “criteria”; and so on) or not at all (e.g., “this sheep” : “these sheep”). Within the post-Bloomfieldian framework no very satisfactory account of the formation of these nouns could be given. But it was clear that they contained (in some sense) the same morpheme as the more regular plurals.

Morphs that are in complementary distribution and represent the same morpheme are said to be allomorphs of that morpheme. For example, the regular plurals of English nouns are formed by adding one of three morphs on to the form of the singular: /s/, /z/, or /iz/ (in the corresponding written forms both /s/ and /z/ are written -s and /iz/ is written -es). Their distribution is determined by the following principle: if the morph to which they are to be added ends in a “sibilant” sound (e.g., s, z, sh, ch), then the syllabic allomorph /iz/ is selected (e.g., fish-es /fiš-iz/, match-es /mač-iz/); otherwise the nonsyllabic allomorphs are selected, the voiceless allomorph /s/ with morphs ending in a voiceless consonant (e.g., cat-s /kat-s/) and the voiced allomorph /z/ with morphs ending in a vowel or voiced consonant (e.g., flea-s /fli-z/, dog-s /dog-z/). These three allomorphs, it will be evident, are in complementary distribution, and the alternation between them is determined by the phonological structure of the preceding morph. Thus the choice is phonologically conditioned.

Very similar is the alternation between the three principal allomorphs of the past participle ending, /id/, /t/, and /d/, all of which correspond to the -ed of the written forms. If the preceding morph ends with /t/ or /d/, then the syllabic allomorph /id/ is selected (e.g., wait-ed /weit-id/). Otherwise, if the preceding morph ends with a voiceless consonant, one of the nonsyllabic allomorphs is selected—the voiceless allomorph /t/ when the preceding morph ends with a voiceless consonant (e.g., pack-ed /pak-t/) and the voiced allomorph /d/ when the preceding morph ends with a vowel or voiced consonant (e.g., row-ed /rou-d/; tame-d /teim-d/). This is another instance of phonological conditioning. Phonological conditioning may be contrasted with the principle that determines the selection of yet another allomorph of the past participle morpheme. The final /n/ of show-n or see-n (which marks them as past participles) is not determined by the phonological structure of the morphs show and see. For each English word that is similar to “show” and “see” in this respect, it must be stated as a synchronically inexplicable fact that it selects the /n/ allomorph. This is called grammatical conditioning. There are various kinds of grammatical conditioning.

Alternation of the kind illustrated above for the allomorphs of the plural morpheme and the /id/, /d/, and /t/ allomorphs of the past participle is frequently referred to as morphophonemic. Some linguists have suggested that it should be accounted for not by setting up three allomorphs each with a distinct phonemic form but by setting up a single morph in an intermediate morphophonemic representation. Thus, the regular plural morph might be said to be composed of the morphophoneme /Z/ and the most common past-participle morph of the morphophoneme /D/. General rules of morphophonemic interpretation would then convert /Z/ and /D/ to their appropriate phonetic form according to context. This treatment of the question foreshadows, on the one hand, the stratificational treatment and, on the other, the generative approach, though they differ considerably in other respects.

An important concept in grammar and, more particularly, in morphology is that of free and bound forms. A bound form is one that cannot occur alone as a complete utterance (in some normal context of use). For example, -ing is bound in this sense, whereas wait is not, nor is waiting. Any form that is not bound is free. Bloomfield based his definition of the word on this distinction between bound and free forms. Any free form consisting entirely of two or more smaller free forms was said to be a phrase (e.g., “poor John” or “ran away”), and phrases were to be handled within syntax. Any free form that was not a phrase was defined to be a word and to fall within the scope of morphology. One of the consequences of Bloomfield’s definition of the word was that morphology became the study of constructions involving bound forms. The so-called isolating languages, which make no use of bound forms (e.g., Vietnamese), would have no morphology.

The principal division within morphology is between inflection and derivation (or word formation). Roughly speaking, inflectional constructions can be defined as yielding sets of forms that are all grammatically distinct forms of single vocabulary items, whereas derivational constructions yield distinct vocabulary items. For example, “sings,” “singing,” “sang,” and “sung” are all inflectional forms of the vocabulary item traditionally referred to as “the verb to sing”; but “singer,” which is formed from “sing” by the addition of the morph -er (just as “singing” is formed by the addition of -ing), is one of the forms of a different vocabulary item. When this rough distinction between derivation and inflection is made more precise, problems occur. The principal consideration, undoubtedly, is that inflection is more closely integrated with and determined by syntax. But the various formal criteria that have been proposed to give effect to this general principle are not uncommonly in conflict in particular instances, and it probably must be admitted that the distinction between derivation and inflection, though clear enough in most cases, is in the last resort somewhat arbitrary.

Bloomfield and most other linguists have discussed morphological constructions in terms of processes. Of these, the most widespread throughout the languages of the world is affixation; i.e., the attachment of an affix to a base. For example, the word “singing” can be described as resulting from the affixation of -ing to the base sing. (If the affix is put in front of the base, it is a prefix; if it is put after the base, it is a suffix; and if it is inserted within the base, splitting it into two discontinuous parts, it is an infix.) Other morphological processes recognized by linguists need not be mentioned here, but reference may be made to the fact that many of Bloomfield’s followers from the mid-1940s were dissatisfied with the whole notion of morphological processes. Instead of saying that -ing was affixed to sing they preferred to say that sing and -ing co-occurred in a particular pattern or arrangement, thereby avoiding the implication that sing is in some sense prior to or more basic than -ing. The distinction of morpheme and morph (and the notion of allomorphs) was developed in order to make possible the description of the morphology and syntax of a language in terms of “arrangements” of items rather than in terms of “processes” operating upon more basic items. Nowadays, the opposition to “processes” is, except among the stratificationalists, almost extinct. It has proved to be cumbersome, if not impossible, to describe the relationship between certain linguistic forms without deriving one from the other or both from some common underlying form, and most linguists no longer feel that this is in any way reprehensible.