This paper discusses the concept of error in the learning of the phonology of a second language and argues that the concept of error must be viewed as a positive element, an initiation of the process of successive approximations toward the correct phonetic realization. Based on the idea that interference between two languages generates a predictable "system of errors," a "system of errors" is presented for English-speaking North Americans learning French phonology. Although such a system cannot account for all possible errors, it serves as a guide for the teacher who needs to discern phonetic errors in his pupils. (AM)