 However, the argument from the need to provide psychological explanations of the behavior of nonhuman animals and human infants to the existence of nonconceptual content does not stand or fall with the thesis that concepts are necessarily linguistic. It has been argued that there is a distinction between two different types of thinking (Mithen 1996). Many students of the type of cognition engaged in by animals and infants view it as being domain-specific and modular in important respects, best understood in terms of bodies of “knowledge” closely focused on particular aspects of the natural and social worlds. An example of such domain-specificity is found in the perceptual module Spelke suggests is responsible for the segmentation of the visual array into objects according to certain basic physical principles (Spelke 1990, 1994, Carey and Spelke 1996). These domain-specific modules are thought to have evolved separately and for specific purposes and are not integrated with each other (Hirschfeld and Gelman 1994). In contrast, many philosophers have suggested that the type of conceptual thought engaged in by language-users is essentially domain-general, systematic and productive. Concept-possessors can generate an indefinite number of new thoughts from the concepts they possess and their thoughts obey what Evans (1982) has termed the generality constraint. As Evans says, “We cannot avoid thinking of a thought about an individual object x, to the effect that it is F, as the exercise of two separable capacities; one being the capacity to think of x, which could be equally exercised in thoughts about x to the effect that it is G or H; and the other being a conception of what it is to be F, which could be equally exercised in thoughts about other individuals, to the effect that they are F” (Evans 1982, p. 75).