Suppose we separate mind and world in the manner prescribed by Cartesian internalism. A mind is an interiority: mental phenomena are located exclusively inside the skin of any organism that possesses them, and possession of such phenomena by a creature is logically independent of whatever exists or occurs in the world outside that skin. Then we are immediately presented with a problem, one that has been and continues to be enormously influential. It is sometimes called the matching problem. The matching problem, then, is a direct result of the sort of separation of mind and world essential to Cartesian internalism. And this result of internalism leads to a response: the transcendental idealism of Kant and a succession of imitators. Idealism – the view that reality is in one or another way, and to a greater or lesser degree, mental – is, therefore, a direct result of internalism. This matters – because idealism has provided the dominant intellectual Weltanschauung of the twentieth century, and not only in philosophy. And there is, I think, little current evidence of its decline.

The transition from Cartesian internalism to neo-Kantian idealism and the debilitating excesses of recent versions of this idealism are the subject of this chapter. These excesses are precisely the sort of mess one can get oneself into through an uncritical acceptance of the dichotomizing of mind and world along Cartesian internalist lines.

The matching problem

Kant's monumental Critique of Pure Reason is, justifiably, one of the most influential books in the history of philosophy.