The nature of the relationship between the formal theory of learnability (Gold, 1967; Osherson, Stob, & Weinstein, 1986), the theory of grammar, and the theory of acquisition poses a difficult conceptual problem. Ideally, the various studies should reinforce each other in such a way as to converge toward a complete theory of language acquisition. Thus, one would hope to find a great deal of collaboration between the three disciplines. In recent years, developmental psycholinguists have been able to draw on work in generative grammar to inform their research on child language acquisition. Relations have not been so close with formal learning theory, where the mathematical formalism seems to have acted as a hindrance to communication between the disciplines. I argue here, perhaps unoriginally, that the three disciplines cannot be easily separated and that each can draw on the others for insights about the language faculty.