The rules which describe the permitted sequences in studying phonology are call sequence constraints . When an initial consonant cluster of two members in which the second member is r , a phonology rule specifies which sounds can occur before the r . They may also offer an explanation of why the process takes place. The explanation to these two questions is the phenomenon of assimilation , the natural process by which a sound changes in order to become more like another sound. We anticipate a sound and this changes another sound.
Vowels become nasalized because they assimilate to the nasality of a following nasal.
A mental unit of speech is a phoneme . Phonemes are contrastive sound units which make a difference in words. Time, dime, rhyme, lime, chime, and mine are a minimal set. Time and dime are a minimal pair. 14 Morpheme is the smallest unit of linguistic meaning or function.