Abstract

Thought experiments show that people who are physically identical but have different environments can have mental states with different contents. But many philosophers think that physically identical people must also be psychologically identical. They therefore believe these thought experiments show that differences in mental state content do not necessarily mark genuine psychological differences, but are instead merely fallible signs of psychological differences. They conclude that content attributions do not have a fundamental role to play in psychological explanation. ;I argue that persons whose mental states have different contents are also psychologically different. Their mental states differ in their psychologically important causal powers. Their mental states tend to have different environmental causes and effects and tend to have causes and effects with different intentional properties, and these differences are psychologically important. So to distinguish mental states by their contents is to distinguish them by psychologically important properties. I also develop a theory of content suitable for psychological explanation. The theory appears able to distinguish between any two mental states that are psychologically different, even in puzzle cases like Kripke's famous example of Pierre. ;Some critics of content contend that for psychological purposes we need a new notion of content, narrow content, that supervenes on physiology. I critically examine several different theories of narrow content. I divide the theories into two kinds: "indexical" theories and phenomenological theories. Some of these kinds of content do not supervene on physiology. Other kinds of narrow "content" are actually not kinds of content, or have other problems that make them practically unsuitable for psychological theory. ;I conclude that psychology needs broad content , and that it needs no other notion of content.