University of Alberta Dictionary of Cognitive Science: The Disjunction Problem

Any theory of the content of a representation must be able to explain how a representation can misrepresent --how it can represent an object as being something it is not, or as having properties it does not have-- basically how its content can be false of the object represented.

The difficulty is that we need to explain --in a principled, non-circular way-- how the representation can correctly represent some things which cause its activation, yet misrepresent other things which cause its activation. For instance, we'd like to be able to say that my kangaroo representation represents kangaroos. If so, then if a wallaby causes the activation of that representation, then the wallaby is misrepresented; the representation's content that's a kangaroo is false of the wallaby.

Unfortunately, to Fodor (1987, 1990) this doesn't work. The problem is that if the wallaby can also cause the activation of my kangaroo representation, then we seem to have no principled reason for saying that the content of the representation is simply that's a kangaroo rather than the disjunctive content that's either a kangaroo or a wallaby. If this is so, then when a wallaby activates my kangaroo representation, this representation doesn't represent the wallaby as something it is not. This representation has the (disjunctive) content that's either a kangaroo or it's a wallaby which, of course, is true of the wallaby.

This is especially a problem for theories which explain content in terms of covariance: some sort of reliable, lawlike, connection between tokenings of the representation and the occurrence of certain types of thing in the world. Such theories have to be able to justify describing the representation's content "conservatively" as Cummins (1990) calls it, rather than "liberally"; as that's a kangaroo rather than that's a large animal with a long tail that gets about by hopping on its hind legs. Cummins summarises various attempts to do this, arguing that covariance theories don't explain content in a way that allows representations to misrepresent.

Fodor (1990) claims that any theory which purports to account for the content of a representation must solve the disjunction problem. Such an account must be able to explain misrepresentation, by showing what a representation's content is--exactly-- and also how a representation can be caused to be activated by something to which that content does not apply.

References:

Cummins, R. (1989). Meaning and Mental Representation. Cambridge, Mass: MIT Press. A Bradford Book.
Fodor, J. (1987). Meaning and the World Order. In Psychosemantics (pp. 97-133). Cambridge Mass.: MIT Press. A Bradford Book.
Fodor, J. (1990). A Theory of Content I: The Problem. In A Theory of Content and Other Essays. (pp. 51-88). Cambridge, Massachusetts: MIT Press. A Bradford Book.

(Revised December 2009)