Morphology is the branch of linguistics that deals with the internal structure of those words that can be broken down further into meaningful parts. Morphology is concerned centrally with how speakers of language understand complex words and how they create new ones. Compare the two English words marry and remarry. There is no way to break the word marry down further into parts whose meanings contribute to the meaning of the whole word, but remarry consists of two meaningful parts and therefore lies within the domain of morphology. It is important to stress that we are dealing with meaningful parts. If we look only at sound, then marry consists of two syllables and four or five phonemes, but this analysis is purely a matter of PHONOLOGY and has nothing to do with meaningful structure and hence is outside morphology.

The first part of remarry is a prefix (re-), which means approximately 'again'; it is joined together with the second component, the verb marry, to form another verb with the predictable meaning 'marry again'. The same prefix re- occurs in many other words (e.g., reacquaint, redesign, refasten, and recalibrate) and can also be used to form novel words like redamage or retarget whose meaning is understood automatically by speakers of English. The additional fact that verbs like *reweep or *relike are impossible tells us that there are restrictions on this prefix. It is the morphologist"s job to discover the general principles that underlie our ability to form and understand certain complex words but not others.

Languages differ quite greatly in both the complexity and the type of their morphology. Some languages (e.g., Mandarin Chinese and Vietnamese) have very little in the way of morphology. Others (e.g., Turkish, Sanskrit, Swahili, and Navajo) are famous for their complex morphology. English falls somewhere in the middle. It is quite normal for an English sentence to contain no complex words. Even Shakespeare, who is commonly thought of as using complex language, tended to use morphologically simple words. That most famous of Shakespeare"s sentences, "To be or not to be, that is the question," is morphologically very simple.

The atomic meaningful units of language are traditionally called morphemes. Morphemes are classified into two very basic types: free morphemes and bound morphemes, the difference between them being that a bound morpheme is defined in terms of how it attaches to (or is bound to) another form (called its stem). The most common types of bound morphemes are prefixes and suffixes. The other major device for forming complex words in English is compounding, whereby free morphemes are put together to form a word like doghouse or ready-made. Although these devices are quite simple, repeated application allows for the formation of fairly complex words by piling one prefix or suffix on another or by successive compounding. The word unmanageableness contains three bound morphemes and has been built up in stages from manage by first adding the suffix -able to produce manageable, then the prefix un- to form unmanageable, and finally the suffix -ness, resulting in [[un[[manage] Vable] A]Aness] N.

Among the world"s languages, suffixation is the most common morphological device and there are quite a few languages (including Japanese, Turkish, and the very large Dravidian family of South India) that have no prefixes but permit long sequences of suffixes. Languages with many prefixes and few or no suffixes are quite rare (Navajo is one example). Some languages use infixes, which are placed at a specific place inside their stems. In Tagalog, the national language of the Philippines, for example, the infix -um- may be added in front of the first vowel of a stem, after any consonants that may precede it, to mark a completed event. Alongside takbuh 'run' and lakad 'walk,' we find tumakbuh 'ran' and lumakad 'walked'. Another internal morphological device is to change a sound in the stem. A fairly small number of English verbs form their past tenses by changing the vowel: write/wrote, sing/sang, hold/held. These are irregular in English, because the vast majority of English verbs form their past tense by suffixation, but in some languages, most prominently the Semitic languages, this type of vowel substitution is normal. Consonants as well as vowels may be altered in a meaningful way. One example of this in English is the relation between nouns like cloth that end in voiceless fricatives (in which there is no vibration of the vocal folds) and corresponding verbs like clothe, which end in the corresponding voiced fricative sound. Bound morphemes thus modify the sound shape of the words to which they attach, either by adding something to the stem or by changing it. In the limiting case, known as conversion, there is no change at all in the shape of the word. This device is very common in English, where basic nouns like ship and sand are routinely turned into verbs, and verbs like run can similarly be turned into nouns.

Linguists distinguish derivational morphology from inflectional morphology. Derivational morphology, as just discussed, deals with how distinct words (lexemes) are related to one another; inflectional morphology is concerned with the different forms that a word may take, depending on its role in a sentence. English is quite poor inflectionally. Nouns have at most a singular and a plural form, and only pronouns have special case forms that depend on the role of the word in a sentence; regular verbs have only four distinctive forms, and the different tenses, aspects, and moods are formed by means of auxiliary verbs. But in many other languages, all nouns have distinct case forms, adjectives must often agree with the nouns that they modify, and verbs may have not only distinct forms for each TENSE AND ASPECT, voice and mood, but may also agree with their subject or object. In Classical Greek, each noun will have 11 different forms, each adjective 30, and every regular verb over 300. Other languages are even more complex in their inflection.

An important difference between morphology and SYNTAX is that morphological patterns vary greatly in their productivity, the ease with which new words can be created and understood. If we compare the three English noun-forming suffixes -ness, -ity, and -th, we find that there are many existing nouns ending in -ness, a somewhat smaller number ending in -ity, and only a dozen or so nouns ending in -th. The numbers correlate roughly with the productivity of new words: experiments show that a new noun ending in -ness will be more readily accepted as English than a new noun ending in -ity, and no new noun in -th has been added to the language since about 1600.

The study of productivity shows that the distinct lexemes and their forms comprise a complex network. A major research focus for the experimental study of morphology has been the nature of this network. The prevailing model is that speakers each have a mental LEXICON in which is stored every word of their language, inflected or derived, that has any unpredictable feature. Completely regular words are produced on the fly by productive patterns as they are needed and then discarded. Less productive patterns may also be used, but the words formed in these patterns are less predictable in their meaning and are more likely to be stored once they have been used.

Morphology lies at the heart of language. It interacts with syntax, phonology, SEMANTICS, PRAGMATICS, and the lexicon. Through this interaction, it also relates to numerous aspects of NATURAL LANGUAGE PROCESSING and cognition. Morphology can thus provide a window onto detailed aspects of language and cognition. The more we discover about the rest of language and cognition, the more important the study of morphology will become.

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-- Mark Aronoff

Further Readings

Aronoff, M. (1976). Word Formation in Generative Grammar. Cambridge, MA: MIT Press.

Bauer, L. (1983). English Word-Formation. Cambridge: Cambridge University Press.

Carstairs-McCarthy, A. (1992). Current Morphology. London: Routledge.

Feldman, L. B., Ed. (1995). Morphological Aspects of Language Processing. Hillsdale, NJ: Erlbaum.

Matthews, P. H. (1991). Morphology. 2nd ed. Cambridge: Cambridge University Press.

Mel'cuk, I. A. (1992). Cours de Morphologie Générale, vol. 1. Montreal: Presses de l"Université de Montréal.

Nida, E. A. (1949). Morphology: The Descriptive Analysis of Words. 2nd ed. Ann Arbor: University of Michigan Press.

Scalise, S. (1986). Generative Morphology. Dordrecht: Foris.

Spencer, A. (1991). Morphological Theory. Oxford: Blackwell.

Zwicky, A., and A. Spencer, Eds. (1998). Handbook of Morphol ogy. Oxford: Blackwell.