An example. Supposing I am designing a first-year syllabus for ten-year olds learning English as a foreign language. Frequency studies might indicate that words like crocodile, elephant, and butterfly are far less commonly used than words like engine, wheel, seat, (West, 1953). If we design our syllabus according to linguistic considerations, we will naturally prefer to teach the more common words earlier. But crocodile etc. appeal to children both because of their meaning and because they are fun to (try to) say: and a reliable pedagogical principle is that children tend to learn more easily, words that appeal to them. As a teacher, I am interested in my students’ motivation and rapid acquisition of new vocabulary which they can use to say things, as much as in the usefulness of that vocabulary. So I may well prioritize the less common words.