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.