Behaviorism is a theory based upon habit formation. After receiving input from the target language, whether read or heard, the learner then attempts to mimic the sounds heard. When the learner correctly uses the language, positive feedback is given, and habits are formed. These habits are eventually strengthened to the point of fluency. This is extended to S.L.A. with the idea that habits from the first language either aid, or interfere with the development of habits in the second language, which would be perceived in errors made in the second language or L2.

In the context of S.L.A. this theory does not explain things to a satisfactory degree. If interference arises in the habit formation of a learner attempting to develop fluency in his/her target language, then speakers of that target language should be expected to have the same interference kind of interference when learning our speaker's L1. However this has not shown to be the case. Therefore, there must more going on than simple habit formation.