When we introduced the symbol /l/, we noted that linguists usually distinguish between two varieties, known as clear and dark (p. 47). The two varieties never contrast with each other in English and so are never responsible for creating differences in meaning. This is because the two varieties are distributed differently in English words; the distribution of the clear /l/ is confined to a position before vowels (and before /j/), and the distribution of the dark /l/ to a position before consonants (except /j/) and at the end of words. The distribution of the one variety complements the distribution of the other – they can never occur in exactly the same position as the other. That is why they cannot clash, and that is why they are considered as varieties of one phoneme (in English). A phoneme is the basic unit in the phonological system of a language.