We must frankly admit that the "transfer theory", on which some fundamental ideas of contrastive linguistics are based, is currently in disrepute among many psychologists. Moreover, it might be a gross oversimplification simply to assert that prior learning affects subsequent learning, positively when the learning tasks coincide and negatively when they differ. However, we so often come across cases where structural differences and similarities between a learner\u27s native and target languages are too obviously reflected in the way he learns the latter and uses it, that we can hardly deny the validity of the theory. The reason why the scientific and practical results of work in this field have not matched early expectations, might be found in the fact that the causes of errors were exclusively sought in this psychological aspect. We should remember there are a variety of factors which influence the process of learning. For example, an investigation of errors reported by some teachers of English referred not only to errors based on the overgeneralization of patterns learned earlier, but also to errors based on incomplete acquisition of such patterns and failure to recognize semantic distinction. Errors of this type, some linguists argue, are often more appropriately viewed positively, as reflecting creative strategies of the learner aimed at discovering the grammatical structure of the target language. This reveals the innate competence of the learner for language acquisition, and the teacher should adapt his strategies to those of the learner. Therefore the attribution of interference then becomes another problem, that of whether the interference represents influence from the native language or from earlier-acquired knowledge of the target language. Thus far I have made a series of investigations, taking as a basis the former, in other words, to determine what influence a learner\u27s mother tongue will exert on his learning of English. They are intended to provide the teacher with useful information for more efficient and effective teaching strategies. This time my inquiry will be focused on the learning of Modals in English. As the Japanese language lacks the exact counterparts of English Modals, "translation equivalence" will be used as a criterion. The items to be discussed are as follows : -I. Ambiguity in the meaning of English Modals II. Syntactic features of Modals III. Semantic features of Modals IV. Japanese "translation equivalence" of Modals V. Syntactic restraints on Modals VI. Modals and Negation VII. Modals and Tenses VIII. Quasi-modals IX. Verificatio
