Morphology is a subdiscipline of linguistics that studies word structure. Words are at the interface among phonology, syntax and semantics (Spencer / Zwicky).
There are many current approaches to morphology. For expository purposes, this article will describe the phenomena in a fairly traditional way: treating words as combinations of discrete meaningful units (morphemes) put together by concatenation. A contemporary morphologist would call this a "morpheme-based" theory; alternatives are lexeme-based morphology and word-based morphology.
The components of a word form are called morphemes. Word formation rules describe how to select morphemes from the lexicon and to combine them.
Morphemes make up words and are the smallest units of grammar: roots, prefixes, and suffixes. Native speakers recognize the morphemes as grammatically significant or meaningful. For example, "schoolyard" is made of "school" + "yard", "makes" is made of "make" + a grammatical suffix "-s", and "unhappiness" is made of "happy" with a prefix "un-" and a suffix "-ness".
Inflection occurs when a word has different forms but essentially the same meaning, and there is only a grammatical difference between them: for example, "make" and "makes". The "-s" is an inflectional morpheme.
In contrast, derivation makes a word with a clearly different meaning: such as "unhappy" or "happiness", both from "happy". The "un-" and "-ness" are derivational morphemes.
These examples also illustrate the other two kinds of morphemes, unbound (which are meaningful on their own) and bound (which have meaning when combined with another morpheme). Thus, the word "schoolyard" consists of two unbound morphemes ("school" and "yard"), while the word "makes" has one unbound ("make") and one bound, and "unhappiness" has one unbound and two bound.
A word may consist of two bound morphemes: the word "morpheme" itself illustrates this, since it consists, or traditionally consisted, of two bound morphemes ("morph" and "eme"). But as the example of "morpheme" reveals, bound morphemes may become unbound ones: "morph" has been adopted in linguistics for the phonological realization of a morpheme, and the verb "morph" was coined to describe a transition between morphological states (usually biological). A more familiar example is if we adopt the suffix "-ish" as a separate word, and use "ish" by itself to mean "somewhat, a bit, so-so". The suffix "-ism" is often applied in a similar way to mean "a system of beliefs or an ideology" (e.g. Darwinism).
A morpheme may have different realizations (morphs) in different contexts. For example, the verb morpheme "do" of English has three quite distinct pronunciations in the words "do", "does" (with suffix "-s"), and "don't" (with "-n't"). Such alternating morphs of a morpheme are called its allomorphs. Other examples are in past participles of verbs: "walked", "eaten", "drunk": one verb has a regular "-ed" allomorph, one has a less common "-en" allomorph, and one changes the vowel inside the verb. This last case is a problem for description, because you can't separate the morpheme "drink" from the morpheme for past participle. The two appear fused.
In some languages, of which Latin forms a prime example, several inflections are often fused into one phonetic form. These are called fusional languages. For example, dominus "master" has plural domini, while domina "mistress" has plural dominae. The ending -us contains the ideas of masculine and singular, and in addition is only used in the nominative case. In the accusative singular it is dominum, and in the genitive plural it is dominorum. It is impossible to isolate separate morphemes for case, or gender, or number. In contrast to fusional languages, agglutinative languages such as Turkish use multiple morphemes in the one word but they are all phonetically separable.
The Semitic languages show an extreme of fusion, in that word roots are often represented by fixed consonants, usually three, and their inflection and derivation is done with internal vowel patterns as well as affixes. For example, in Arabic we find kataba "he wrote", yaktubu "he writes", kaatib "writer", kitaab "book", maktab "office". All these forms use the consonant cluster KTB.
Suppletion is the replacement of a regular form by an unrelated word. In English "go" has the past tense "went", and "be" has various unrelated parts such as "am" and "was".
The term Gesamtbedeutung is used to describe the general semantic meaning of a particular morpheme, independent of grammatical function. The morphemes "-ing" and "-or" (as in "eliminating" and "eliminator") may be said to share a common Gesamtbedeutung, namely that of agency.
A cranberry morpheme is one that exists only in one bound form, such as the "cran-" of "cranberry". It is unrelated to the word "cran" meaning a case of herrings, and though it actually comes from "crane" the bird, it is not at all clear why. Phonetically, the first morphemes of "gooseberry" and "raspberry" also count as cranberry morphemes, as they don't occur by themselves, but the spelling gives an obscure clue to their origin. Compare these to "blackberry", which has two obvious unbound morphemes.
- Peter H. Matthews' Morphology (ISBN 0521422566) is a classic late 20th century introductory textbook.
- Francis Katamba, Morphology, Macmillan Press, 1993
- Peter H. Matthews, Morphology, 2nd Ed., Cambridge University Press, 1991.
- Andrew Spencer and Arnold M. Zwicky, The Handbook of Morphology, Blackwell, 1998