Conditioning involves the strengthening of associations between a stimulus and a response through reinforcement. Human language is a sophisticated response system acquired through operant conditioning. Universal Grammar Theory posits the existence of a set of basic grammatical elements or fixed abstract principles that are common to all natural human languages and that predispose children to organize the input in certain ways. Hmm. . . Language is a species-specific, genetically determined capacity.
Language learning is governed by biological mechanisms.
Core grammar rules are thought to be relatively easier to acquire, in general, than peripheral rules. SLA is based on acquisition. Learning involves conscious learning of rules. When acquisition is natural, the order in which certain grammatical features of the language are acquired is predictable. Input does not need to be deliberately structured or planed for the acquirer.