 There are two problems with this argument, however. The first problem has to do with the third premise, which states that tractability requires encapsulation, that is, the inaccessibility of at least some exogenous information to processing. What tractability actually requires is something weaker, namely, that not all information is accessed by the mechanism in the course of its operations (Samuels, 2005). In other words, it is possible for a system to have unlimited access to a database without actually accessing all of its contents. Though tractable computation rules out exhaustive search, for example, unencapsulated mechanisms need not engage in exhaustive search, so tractability does not require encapsulation. The second problem with the argument concerns the last step. Though one might reasonably suppose that modular systems must be encapsulated, the converse doesn’t follow. Indeed, Carruthers (2006) makes no mention of encapsulation in his characterization of modularity, so it’s unclear how one is supposed to get from a claim about pervasive encapsulation to a claim about pervasive modularity. 