In the physical world the native speaker and hearer actualize and are sensitive to sounds, but what they feel themselves to be pronouncing and hearing are 'phonemes'
Edward Sapir
Phonological knowledge goes beyond the ability to produce all the phonetically different sounds of a language. It includes this ability, of course. A speaker of English can produce the sound [
θ] and knows that this sound occurs in English, in words such as thin [θɪn], either [iθə], or bath [baθ]. English speakers may or may not be able to produce a 'click' or a velar fricative, but even if they can, they know that such sounds are not part of the phonetic inventory of English. Many speakers are unable to produce such 'foreign' sounds. A speaker of English also knows that [ð], the the voiced counterpart of [θ], is a sound of English, occurring in words such as either [iðə], then [ðe~n], and bathe [beɪð]. Similarly, French speaker know that [ð] and [θ] are not part of the phonetic inventory of French and often find it difficult to pronounce words such as this [ðɪs] and that [ðæt], pronouncing them as if they were spelt zis and zat.
