After decades of work, it is not clear—at least to me—that we have anything like a coherent theory of the complex domains of language learning and language teaching. It is perhaps the case that—like other areas of science (e.g., psychology)—we have been misled by taking the everyday meanings of words (in this case, words like “learning”, “development”, “acquisition”, “teaching”, and “language”) too seriously as good guides for how to categorize the data and phenomena with which we are faced.