PHONOLOGY

Phonology is a study of systematic relationship between sounds,including contrast,positional variation,phonotactic,restrictions,and alternations.
Phonetics illusions and the mistakes of language learners clue us in to the necessity of a level of phonologycal knowledge more abstract than actual pronunciation . contrast and positional variation can be studied through phonemic analysis, which was a particular hallmark of a structualist approach. A phoneme is a unit of contrast (that is,a “family” of sounds that all “count as the same”). The allophones of a phoneme are the positional variants that make up the phoneme.

Minimal pairs diagnose different phonemes , complementally distribution diagnoses allophonic status. The basic of underlying form of a phoneme typically corresponds to the “elsewhere case” but a more abstract  underlying form is sometimes necessary or preferable.

Free variation and positional neutralization complicate phonemic analysis, because they create an unprecditable mapping between allophone and phoneme.in the first half of the twentieth century,structualism and behaviorism were the dominant theories in phonology,both of which emphasized relationships among surface forms. In the second half of the twentieth century,phonologist began to focus more on the question of linguistic knowledge, andthe on mapping from underlying to surface respresentations.