Human beings approach any new problem with an existing set of cognitive structures and through insight, logical thinking, and various forms of hypothesis testing, call upon whatever prior experiences they have had and whatever cognitive structures they possess to attempt a solution. In the literature on language learning processes, three terms have commonly been singled out for explication: transfer, interference, and overgeneralization. The three terms are sometimes mistakenly considered to represent separate processes; they are more correctly understood as several manifestations of one principle of learning—the interaction of previously learned material with a present learning event. From the beginning of life the human organism, or any organism for that matter, builds a structure of knowledge by the accumulation of experiences and by the storage of aspects of those experiences in memory. Transfer is a general term describing the carryover of previous performance or knowledge to subsequent learning. Positive transfer occurs when the prior knowledge benefits the learning task, that is when a previous item is correctly applied to the present subject matter. Negative transfer occurs when previous performance disrupts the performance of a second task. The latter can be referred to as interference, in that previously learned material interferes with subsequent materials—a previous item is incorrectly transferred or incorrectly associated with an item to be learned. In the literature of second language acquisition, interference is almost as frequent a term as overgeneralization, which is a particular subset of generalization. In second language acquisition, it has been common to refer to overgeneralization as a process that occurs as the second language learner acts within the target language, generalizing a particular rule or item in the second language—irrespective of the native language—beyond legitimate bounds.