Morpheme

In linguistics, a morpheme is the smallest grammatical unit in a language. In other words, it is the smallest meaningful unit of a language. The field of study dedicated to morphemes is called morphology. A morpheme is not identical to a word, and the principal difference between the two is that a morpheme may or may not stand alone, whereas a word, by definition, is freestanding. When it stands by itself, it is considered as a root because it has a meaning of its own (e.g. the morpheme cat) and when it depends on another morpheme to express an idea, it is an affix because it has a grammatical function (e.g. the –s in cats to indicate that it is plural). Every word comprises one or more morphemes.

Every morpheme can be classified as either free or bound. These categories are mutually exclusive, and as such, a given morpheme will belong to exactly one of them.

Bound morphemes can be further classified as derivational or inflectional.

Allomorphs are variants of a morpheme that differ in pronunciation but are semantically identical. For example, in English, the plural marker -(e)s of regular nouns can be pronounced /-z/, /-s/, or /-ɪz, -əz/, depending on the final sound of the noun's singular form.For example, plural ending s (as in bats), z (as in bugs), iz (as in buses).

Generally these types of morphemes have no visible changes. For instance the singular form of sheep is "sheep" and its plural is also "sheep". The intended meaning is thus derived from the co-occurring determiner (e.g. in this case "some-" or "a-").

Content morphemes express a concrete meaning or content, while function morphemes have more of a grammatical role. For example, the morphemes fast and sad can be considered content morphemes. On the other hand, the suffix –ed belongs to the function morphemes given that it has the grammatical function of indicating past tense. Although these categories seem very clear and intuitive, the idea behind it can be harder to grasp given that they overlap with each other. Examples of an ambiguous situation are the preposition over and the determiner your, which seem to have a concrete meaning, but are considered function morphemes because their role is to connect ideas grammatically. A general rule to follow to determine the category of a morpheme is:

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