The subject of phonology mainly deals with the segmental side of pronunciation: the vowels, the consonants, and the way vowels and consonants combine to make syllables and, ultimately, words. It is very much a rule-governed system. We cannot string sounds randomly together to make syllables. In English, certain sounds never appear at the beginnings of words: there are none beginning with the sound [ŋ]; that sound is heard in the middle and end only (as in singing). A h sound (as in happy) is never heard at the end of a word. A sh sound (as in ship) is heard very rarely before a p, t, or k – just in a few recent loan-words, such as spiel. And so on.

Differences in regional or social accent are mainly a matter of vowels and consonants (though tone of voice can be important too). The prestige British accent known as ‘received pronunciation’ (RP) pronounces h at the beginning of words, as in hurt, and avoids it in such words as arm. Cockney speakers do the reverse; I 'urt my harm. Most English accents around the world pronounce words like car and heart with an audible r; RP is one of the few accents which does not. In RP, words like bath are pronounced with a ‘long a’ (‘bahth’); up north in England it is a ‘short a’. Accent variations mainly affect the vowels of a language. They are easy to hear, but difficult to write down without mastering a phonetic transcription.