The research on which this study is based found that 50% of the errors in English of French-speaking students were due to interlingual causes and 50% had their source within the target language itself. The question of a correlation between the errors and the teaching method used is explored. Five methods are discussed and evaluated: grammar-translation, direct, audiolingual, transformational grammar, and cognitive code. In each case, a correlation is made of the method with varieties and frequency of errors, and the value of elements of the method is noted. Other pedagogical implications are drawn from the study of the frequency of errors for fifteen types of errors, chosen as representatives of important classes of grammar or as general trouble makers. Rank-ordered lists are provided as well as tables and graphs illustrating the relative frequency of the errors. Some of the conclusions are that negative transfer is an important source of errors and that, with regard to intralingual errors, overgeneralization seems to be the most common cause. To reduce errors of all types and promote communication and fluency, an eclectic method is suggested. It is also noted that some errors persist on all levels even after many years of study. (AMH)