 Perhaps the most influential discussion of concepts in relation to the nativism/empiricism debate is Jerry Fodor’s (1975, 1981) argument for the claim that virtually all lexical concepts are innate. Fodor (1975) argued that there are theoretical problems with all models of concept learning in that all such models treat concept learning as hypothesis testing. The problem is that the correct hypothesis invariably employs the very concept to be learned and hence the concept has to be available to a learner prior to the learning taking place. In his (1981), Fodor developed this argument by allowing that complex concepts (and only complex concepts) can be learned in that they can be assembled from their constituents during the learning process. He went on to argue that lexical concepts lack semantic structure and consequently that virtually all lexical concepts must be innate—a position known as radical concept nativism. Fodor’s arguments have had a great deal of influence on debates about nativism and concept learning, especially amongst cognitive scientists. Few if any have endorsed Fodor’s radical conclusions, but many have shaped their views of cognitive development at least in part in response to Fodor’s arguments (Jackendoff 1989, Levin &amp; Pinker 1991, Spelke &amp; Tsivkin 2001, Carey 2009). And Fodor has convinced many that primitive concepts are in principle unlearnable (see, e.g., Pinker 2007). Fodor’s arguments for this conclusion, however, can be challenged in a number of ways. The most direct way to challenge it is to construct an account of what it is to learn a primitive concept and to show that it is immune to Fodor’s challenges (Margolis 1998, Laurence &amp; Margolis 2002, Carey 2009).