In this part，association，behaviorism and mentalism have been discussed.From the discussions，a summary may be made in the following：

To describe how knowledge was created，the empiricists who claimed that knowledge is derived from experience exclusively formulated the laws of association，which included the laws of similarity，contiguity，and cause and effect.

Palmer and Redman single out one statement as the most adequate viewpoint to which they give their full support：it describes the essentials of the language learning process as‘fusing linguistic symbols to the things symbolized’，and any device that will aid in bringing about this fusion，bond，or association as quickly and economically as possible is in their new appropriate.In other words，Palmer like Sweet subscribes to an associationist psychology of second language learning.

In Palmer's view（1922/1964），the language learning process had a natural basis in man's‘spontaneous capacities for acquiring speech’.Nevertheless，this had to be combined with the use of‘studial capacities’，i.e.，deliberate，cognitive，co-operative learning.Palmer was firmly convinced that the learning processes most appropriate for language learning are those that lead to habit formation and‘automatic’unconscious use rather than those that lead to concept formation and systematic thought.

Behaviorists think foreign-language learning is basically a mechanical process of habit formation.More deeply committed to such a point of view is Nelson Brooks：“The single paramount fact about language learning is that it concerns，not problem solving，but the formation and performance of habits.”（Brooks，1960：46-7）Analogies between language and‘other skills’abound.Learning a language is like learning to type，to ride a bicycle or to carry out any of the other routines that we characterize as habits.They are forms of human activity，which，once learned，can be learned out without the conscious use of one's cognitive processes.The belief is that conscious attention to the principles underlying the skill does not assist the learning of the skill；learning is controlled by the conditions under which it takes place and that，as long as individuals are subjected to the same conditions，they will learn in the same way.What appears to be variation in learning ability is really no more than different learning experience；every utterance and every part of an utterance is produced as the result of the presence of some kind of‘stimulus’.The stimulus，to which the utterance forms a‘response’，may be physically present in the situation；the notion of repetition is extremely important；all the responses in any one drill will have exactly the same grammatical structure.With enough properly reinforced repetition of the structure，the‘rule’will be acquired in a way that is not only unconscious but also more conducive to spontaneous language use thereafter；the more complex the stimuli and responses one gets，the more complex learning becomes.

As for mentalism，Chomsky argues that human behavior is considerably more complex than animal behavior.Moreover，certainly language behavior is so specific to humans that it could never be explained through animal behavior.According to Chomsky，a description of language behavior cannot be just a description of external stimuli and concomitant responses，but it primarily has to be a description of the innate ability of human beings to learn a language；Chomsky's Language Acquisition Device or LAD enables the child to make hypotheses about the structure of language in general，and about the structure of the language it is learning in particular.This is not a conscious process.The hypotheses the child subconsciously sets up are tested in its use of language，and continuously matched with the new linguistic input that the child obtains by listening to what is said in its immediate environment.This causes the child's hypotheses on the structure of language to be changed and adapted regularly：the child develops its rule system through a process of systematic changes towards the adult rule system.

All in all，in comparison with behaviorism and mentalism，it seems that the theory of behaviorism is too slender indeed，and that it's the mentalism that can support the application of the GT Method.

To take the decision to base one's teaching exclusively behaviorism or mentalism on one or other of these theories would be quite unjustified in the present state of our knowledge.If one enquires into the empirical basis for either theory，one will find that they are rather weak.The experimentation that lies behind the behaviorist view is with animals and obviously is not itself concerned with language behavior.The extension to first language learning depends on the assumption that the same principles apply to language learning as to the learning by rats of how to find their way through a maze.This may not seem a particularly reasonable assumption，but it is possible that some of the principles do operate even if they cannot account for language learning entirely.Language teachers had arrived at not dissimilar ideas on the basis of their practical experience.

As for the mentalist theory，it at least is intended to account for human behavior.The empirical evidence for it is very slender indeed.It rests on the kind of evidence about child language learning and which seems to be open to alternative explanations，and on universal characteristics of language that seem to require a particular kind of mental structure，which would have to be innate.Even if one accepted the existence of an innate language acquisition device，as a language teacher one would require further evidence that this device was employed not only for the learning of the mother-tongue，but also for foreign languages.It is not unreasonable to ask whether the capacity for language acquisition remains once the first language has been learned，or whether completely different processes are used in the learning of further languages.