Phonetics vs. phonology

Phonetics vs. phonology

Phonetics deals with the production of speech sounds by humans, often without prior knowledge of the language being spoken. Phonology is about patterns of sounds, especially different patterns of sounds in different languages, or within each language, different patterns of sounds in different positions in words etc.

Phonology as grammar of phonetic patterns

The consonant cluster /st/ is OK at the beginning, middle or end of words in English.
At beginnings of words, /str/ is OK in English, but /ftr/ or /tr/ are not (they are ungrammatical).
/tr/ is OK in the middle of words, however, e.g. in "ashtray".
/tr/ is OK at the beginnings of words in German, though, and /ftr/ is OK word-initially in Russian, but not in English or German.
A given sound have a different function or status in the sound patterns of different languages

For example, the glottal stop [] occurs in both English and Arabic BUT ...

In English, at the beginning of a word, [] is a just way of beginning vowels, and does not occur with consonants. In the middle or at the end of a word, [] is one possible pronunciation of /t/ in e.g. "pat" [pa].

In Arabic, // is a consonant sound like any other (/k/, /t/ or whatever): [يktib] "write!", [daيia] "minute (time)", [a] "right".

Phonemes and allophones, or sounds and their variants

The vowels in the English words "cool", "whose" and "moon" are all similar but slightly different. They are three variants or allophones of the /u/ phoneme. The different variants are dependent on the different contexts in which they occur. Likewise, the consonant phoneme /k/ has different variant pronunciations in different contexts.