Unpacking terms: Fundamental Difference Hypothesis

Simplified explanation of the Fundamental Difference Hypothesis. Are L1 and L2 acquisition fundamentally different or similar? Could they be both? The original: Bley-Vroman, R. (1990). The logical problem of foreign language learning. Linguistic Analysis, 20, 3–49. The revised version: Bley-Vroman, R. (2009). The Evolving Context of the Fundamental Difference Hypothesis. Studies in Second Language Acquisition, 31(2), 175-198.