It was commonly believed until fairly recently that learning a language（a mother tongue or a foreign language）was a matter of habit formation.The learner's utterances were thought to be gradually‘shaped’towards those of the language he was learning.With the mother tongue，for example，sounds uttered by the young child that resembled those in the mother tongue were‘reinforced’or rewarded by approval of the parents.It was this rewarding，either by increased attention from the parents or by the child's wants being satisfied，which led in turn to repetitions of the utterance and the subsequent formation of linguistic habits.

This is a very brief and somewhat over-simplified account，but it contains the essence of the‘behaviorist’notion of language learning.For a full account of this view of language learning，see Skinner（1957）.Skinner's definitive statement of the behaviorist theory of language learning held that if language is essentially a set of habits，then when one tries to learn new habits，the old ones will interfere with the new ones.This is what is called‘mother tongue interference’.In the classroom the old habits must be drilled out and a new set of responses must be learnt.The notion of mother tongue interference as a main contributor to errors in learners'use of foreign languages is related strongly to this particular view how human beings learn a language.

In the meantime，the field of language teaching was dominated by the prevailing view of learning at the time—that of behaviorism.The behaviorists held that language acquisition was a product of habit formation.Habits were constructed through the repeated association between some stimulus and some response，which would become bonded when positive reinforced second language learning，was viewed as a process of overcoming the habits of the native language in order to acquire the new habits of the target language.This was to be accomplished through the pedagogical practices of dialogue memorization，imitation and pattern practice.Overlearning and thus automaticity was the goal.The CAH was important to this view of language learning，since if trouble spots in the target language could be anticipated，errors might be prevented or at least held to a minimum.In this way，the formation of bad habits could be avoided.