Introduction. A morpheme is generally described as the smallest unit which carries information about meaning or function in a language. Morphology is the study of how the morphemes of a language can be used to construct words. Note that a morpheme is both the pattern of sounds and the meaning or function associated with them, thus homonyms are treated as distinct morphemes. When the sound pattern alone is distinguished from the morpheme, it is called a morph (just as the sound of a phoneme is called a phone).
1. Allomorphs. Similar to phonemes, a single morpheme may have several phonetic realizations called allomorphs. For example, the morpheme -s marking the English plural can be expressed as [s] in “cats”, [ez] in “misses”, or [z] in “dogs”. Another example is the indefinite article which is realized as “a” before consonants but “an” before vowels.
2. Word Structure. Simple words consist of a single morpheme while complex words are composed of multiple morphemes. A morpheme that can occur as a word by itself is called a free morpheme, while a morpheme that must be attached to another element is a bound morpheme. For example, unbreakable = un (negation) + break + able (adjective). The morphemes “un-” and “-able” are bound morphemes, while “break” is a free morpheme because it can form a word on its own.
The morpheme “break” is also called the root of the word, while “un-” and “-able” are affixes. Roots usually belong to a lexical category such as noun, verb, adjective, etc. Affixes do not belong to a lexical category and are always bound morphemes. There are generally three kinds of affixes. Prefixes are attached to the front of the root, suffixes are attached to the end of the root, and infixes occur within the root. An example of a common infix from the Semitic languages is the reflexive -t-.
2.1. Root-Pattern Morphology. There is another type of morpheme found in the Semitic languages that is not exactly an infix. Instead, there are two-levels of morpheme intertwined. The root morpheme is purely comprised of consonants (usually three consonants), and vowel patterns are then inserted into the root. Note the following example from Arabic:
katab: “He wrote”
kutib: “It was written”
2.2. Ablaut. This two-level morphology is slightly different from the vowel alternation that occurs in English sing/sang/sung. Here grammatical contrast is marked by variation of a single segment, not a whole pattern. Note that the i/a/u variation is not consistent with other roots (hit/hat/hut?). This sort of vowel alteration is often called ablaut.
2.3. Suppletion. Sometimes a grammatical contrast is marked by substituting a completely different form, called suppletion. For instance, English uses went as the past tense form of ‘to go’. Similarly, Biblical Aramaic uses the perfect form of אזל, but the rest of the paradigm of הלך for ‘to go’. These cases are easy to notice as suppletion, but other times it is not so clear whether the contrasting forms may be the result of internal changes (for instance thought as the past tense of ‘to think’).
2.4. Clitics. Often, short unstressed forms can be pronounced together with another element as if they were one word (I am > I’m). This process is called cliticization. A clitic that attaches to the end of a word is an enclitic, one that attaches to the beginning of a word is a proclitic.
The difference between a clitic and an affix is that a clitic is a free morpheme that is merely shortened in speech. However, an affix is a bound morpheme and has a specific relationship with the word to which it is attached.
2.5. Reduplication. When all or part of the base morpheme is repeated to mark a grammatical or semantic contrast, it is called reduplication. Reduplication occurs widely in Semitic and often indicates some sort of plurality or intensification.
3. Derivation and Inflection. Derivation is the process by which the addition of an affix to a base morpheme creates a word with a new meaning or in a new lexical category. For instance, in English the suffix -er can be applied to a verb to create a noun meaning “one who does X”. Thus paint + -er > painter, one who paints. Another example is the use of the suffix -ize to change a noun into a verb, item + ize > itemize.
In contrast, in inflection an affix is used to to indicate grammatical information about the base morpheme, often called the stem. The type of information marked includes gender, number, case, tense, aspect, etc. Thus the plural marker -s in English is inflectional, not derivational.