In the process of learning morphology, students have difficulty in understanding terms such as morpheme, morph and allomorph, they feel confused about the differences between these terms and other terms like phone, phoneme and allophone, and they are totally at a loss about the different types of allomorphy. To help students better understand and distinguish these concepts and help them learn morphology better, this paper first reviewed the definitions of these terms and explained their differences. Then, it highlighted the distinctions between morpheme, morph, allomorph and phoneme, phone and allophone through definitions and examples. Last, it summarized and sorted out the typical types of allomorphy and the reasons behind. To answer these questions, it is found: first, morpheme, an abstract functioning unit, is realized phonologically or orthographically by different morphes, all of which are the allomorphs of the same morpheme, while phoneme, an abstract phonological unit with contrastive value in sound system, is realized by different phones actually produced in the mouth, all of which are allophones of the same phoneme; second, the typical allomorphs of freestanding morphemes are grammatical words such as indefinite article, the accented or weakened forms of the linking verbs, modal words and conjunctions in connected speech, while the typical allomorphs of bound morphemes are the plural forms of nouns {-s}, the past tense of regular verbs {-ed}, the negative prefix of adjective {in-} and the noun suffix {-tion}. Last, most allomorphs are caused by phonological rules and predictable, but some allomorphs such as the past tense and past participle of irregular verbs base on no rules and are thus, unpredictable.
