Morphology is concerned with generalisations about words as lexical signs, in respect of surface form, meaning, distribution and composition. More generally, morphological information is information about semantically relevant word structure; the smallest morphological unit is the morpheme , often defined as the smallest meaningful unit in a language. Morphemes should not be confused with phonological units such as the phoneme syllable and its constituents, which are used for describing the structure of words from the point of view of their pronunciation, without direct reference to meaning. For applications of morphology to speech recognition see [Althoff et al. (1996)], [Bleiching et al. (1996)], [Geutner (1995)].
The domain of morphology may be divided in terms of the functions of morphological operations, i.e. inflectional agreement or congruence vs. word formation, or in terms of the structures defined by morphological operations, i.e. affixation , (prefixation , suffixation, infixation or prosodic modification ) vs. compounding (concatenation of stems or words). These two dimensions can be represented as follows:
| OPERATION | AGREEMENT | WORD FORMATION |
| AFFIXATION | Inflection | Derivation |
| STEM/WORD CONCATENATION | Composition |
There is a gap in the table with regard to the use of stem or word concatenation for agreement; however, so-called periphrastic constructions with verbs, typically with auxiliary verbs and participles or infinitives, may be assigned to this slot, prepositions relate to nouns in a comparable way. Compare English John will come with French Jean viendra, or English Give it to the cook with German Geben Sie es dem Koch. English lacks an inflectional future, but has periphrastic (phrasal) modal or infinitive complement future forms such as John will come tomorrow, John is going to come tomorrow, as well as the present tense as a general or neutral tense form, as in John comes tomorrow (contrast with anecdotal narrative, such as ``You know something? This morning Julie comes in and there's this pigeon sitting on her desk ...'').
There are other intermediate cases which sometimes present difficulties in classification and where the solution is not always immediately obvious:
Traditional treatments often treat these forms together with inflections, presumably because of their regularity and the involvement of suffixation. They are generally better treated as derivations, however, because they have different syntactic distributions from other inflections of the same stems , and may be additionally inflected as adjectives or nouns (cf. the orthographic form of the perfect participle in French with être verbs: Elle est venue - She has come.