Contrastive analysis is the systematic study of a pair of languages with a view to identifying their structural differences and similarities. Historically it has been used to establish language genealogies. Second language acquisition Contrastive analysis was used extensively in the field of second language acquisition (SLA) in the 1960s and early 1970s, as a method of explaining why some features of a target language were more difficult to acquire than others. According to the behaviourist theories prevailing at the time, language learning was a question of habit formation, and this could be reinforced or impeded by existing habits. Therefore, the difficulty in mastering certain structures in a second language (L2) depended on the difference between the learners' mother language (L1) and the language they were trying to learn. History The theoretical foundations for what became known as the contrastive analysis hypothesis were formulated in Robert Lado's Linguistics Across Cultures (1957). In this book, Lado claimed that "those elements which are similar to [the learner's] native language will be simple for him, and those elements that are different will be difficult". While it was not a novel suggestion, Lado was the first to provide a comprehensive theoretical treatment and to suggest a systematic set of technical procedures for the contrastive study of languages. That involved describing the languages (using structuralist linguistics), comparing them and predicting learning difficulties. During the 1960s, there was a widespread enthusiasm with this technique, manifested in the contrastive descriptions of several European languages, many of which were sponsored by the Center for Applied Linguistics in Washington, DC. It was expected that once the areas of potential difficulty had been mapped out through contrastive analysis, it would be possible to design language courses more efficiently. Contrastive analysis, along with behaviourism and structuralism exerted a profound effect on SLA curriculum design and language teacher education, and provided the theoretical pillars of the audio-lingual method. Criticism and its response In its strongest formulation, the contrastive analysis hypothesis claimed that all the errors made in learning the L2 could be attributed to 'interference' by the L1. However, this claim could not be sustained by empirical evidence that was accumulated in the mid- and late 1970s. It was soon pointed out that many errors predicted by Contrastive Analysis were inexplicably not observed in learners' language. Even more confusingly, some uniform errors were made by learners irrespective of their L1. It thus became