谁能用英语解释Morpheme,要求1000字左右的文章

In morpheme-based morphology, a morpheme is the smallest linguistic unit that has semantic meaning. In spoken language, morphemes are composed of phonemes (the smallest linguistically distinctive units of sound), and in written language morphemes are composed of graphemes (the smallest units of written language).

The concept morpheme differs from the concept word, as many morphemes cannot stand as words on their own. A morpheme is free if it can stand alone, or bound if it is used exclusively alongside a free morpheme. Its actual phonetic representation is the morph, with the morphs representing the same morpheme being grouped as its allomorphs.

Definition
A morpheme is the smallest meaningful unit in the grammar of a language.

Discussion
Current approaches to morphology conceive of morphemes as rules involving the linguistic context, rather than as isolated pieces of linguistic matter. They acknowledge that meaning may be directly linked