Phonology is the study of the sounds of human language and their patterns. It includes the study of phonemes, or distinctive sounds, and allophones, or predictable variants of phonemes. Phonotactics examines permissible sound combinations in a language. Morphophonemics describes how sounds change due to neighboring sounds or morphology. For example, the plural morpheme in English can be /s/, /z/, or /əz/ depending on preceding sounds.