Second language acquisition (SLA) is a relatively new field of enquiry. Before the late 1960s, educators did write about L2 learning, but very much as an adjunct of language teaching pedagogy, underpinned by behaviourism, the then-dominant learning theory in psychology. In this view, the task facing learners of foreign languages was to rote-learn and practise the grammatical patterns and vocabulary of the language to be learnt, in order to form new "habits", that is to create new stimulus-response pairings which would become stronger with reinforcement. In order for the "old habits" of the L1 not to interfere with this process by being "copied", or transferred, into the L2, researchers embarked on thorough descriptions of pairs of languages to be learnt, in order to identify areas that are different and would thus be difficult.