It is useful for teaching and learning to divide the vocabulary of English into four groups.

1. The high frequency words. These consist of around 2,000 word families. They are wide range high frequency words that are an essential basis for all language use. They include most of the 176 function words of English. Typically they provide coverage of around 80% of the running words in academic text. The classic collection of these is Michael West's (1953) General Service List of English Words (GSL).

2. The academic vocabulary. This consists of 570 words (Coxhead, 1998) that are reasonably frequent in a wide range of academic texts, but are not so common, although they do occur, in other kinds of texts. Because they provide coverage of around 8.5%–10% of the running words in an academic text, they are very important for learners with academic purposes. They make the difference between 80% coverage (one unknown word in every five running words) and 90% coverage (one unknown word in every ten running words).

3. Technical vocabulary. This differs from subject area to subject area. For any particular subject it consists of probably 1,000 words or less. It could provide coverage of up to 5% of the running words in a text.

4. The low frequency words. These consist of words that are typically vey narrow range and low frequency. Because of the topic of a particular text a small number may occasionally be quite frequent within that text. In general, they consist of words that occur once or twice and then will not be met again for along time. Of the 86,741 different word types in the 5,000,000 running word corpus used in the Carroll, Davies and Richman (1971) count, 40.4% occured only once in that corpus.