Pragmatists generally hold that most debates within the
philosophy of mind are misled and confused debates that most
philosophers would be better off abandoning in favor of more interesting conversations. The question of
mind-body dualism versus
monism, first posed by
Plato and his contemporaries and repopularized by the famous
modernist thinker
Rene Descartes, is one such question that
pragmatists are interested to stop thinking about.
Identity theory (read this excellent node as an introduction to this critique if you need one) is an attempt to theorize (or explain) the relationship between the human mind and the human body, i.e., the human mind and the human brain, i.e., the mental realm of human life and the physical realm. Analytic philosophy generally assumes that there is a serious philosophical problem posed by the apparent disassociation of our mental lives from our physical lives. The problem, supposedly, is this: our mental goings-on aren't explained by the physical theories that explain, in a causal sense, for instance, why we get tired, why bodies are heavy, why 2 and 2 is 4, etc.. Various philosophers have approached this problem in different ways. Descartes, for instance, propounded a theory of mind-body dualism that gripped the philosophical imagination for many years to follow his writing. Descartes held that the mind and the body were two different substances, and in the language of the time this amounted to positing a universe that consisted of two worlds.
In the 1940s and 1950s (and beyond) many analytic philosophers were reluctant to admit that the world contained phenomena that the physical sciences couldn't explain. And so, they put forward many different notions of mind and body, most commonly different forms of monism or mind-brain identity such as type-type identity theory (types of mental representations correspond to types of brain states or token-token identity theory (tokens, instances, of mental representatios and tokens of brain states).
Pragmatists have long rejected the discourse in which this debate is framed and have attempted to show that the debate is practically meaningless. William James wrote that in order for a debate to be meanginful we must be able to show some practical difference from one side or the other being correct. (This is an almost exact quote from Chapter 1 of his excellent introductory text Pragmatism published in 1907.) A pragmatic deconstruction of identity theory debates reveals that whether or not the mind and brain are essentially (substantially, i.e., in substance) different is a meaningless question. What practical differences can we point to if the mind and body are of the same so-called 'substance' or not? What difference does it make in any of our lives?
A large part of the problem is the Cartesian framework in which the debate is rhetorically couched. Descartes took it for granted that there is a metaphysical difference between minds and bodies. For the pragmatist, however, this is a hard notion to swallow. What practical differences are there between minds and brains in the sense in which philosophers consider them? Whereas Descartes posits a mental realm over and above the physical one, a pragmatist would rather just posit one realm, a practical one, i.e. the practical space in which we always already live our lives. And the practical realm is exactly as varied and complex as our practical lives already are--it includes things like brain states (which are practically meaningful in brain cancer research), electrons (meaningful in physics), emotions (meaningful in psychology and relationships with family and lovers, thoughts (meaningful in a very wide variety of contexts). Rather than talking about mind and body as two distinct realms, why not talk about, for instance, our thoughts and bodies as co-existing in the same shared practical space that conditions both of them. The ways we move and organize our thoughts and bodies is, apparently, after all largely a function of our practical involvement with other people and the activities in which we find ourselves taking place.
For instance, that we think that my name is Jacques is a function of the practice or language-game of naming (see Ludwig Wittgenstein) just as well as the fact that I turn my body when I hear the name "Jacques" called. My thinking "I am Jacques" and turning my body on hearing my name are both practical activities conditioned by our particular form of life in which having a name involves such and such social conditioning, etc.. Just as well, my thinking about an apple is not an impractical activity that we must consider in relation to a) my brain, and b) actual physical apples. Rather, it is an activity with a practical context (in this case the context is the trope of example within a roughly philosophical text). The mental representation is not practically meaningful in considering thoughts about apples. What good is a thought standing on its own without a context with which we can understand it?
The pragmatist attempts an understanding of human activity as part of a complex of practices in which humans are always already involved. Re-theorizing these practical relationships as representations that may or may not correspond to brain states that may or may not exist in the physical sense in which some philosophers unscientifically posit them is to do alot of work that is already done in a different way. If you want to understand why water is formed by two H and O (H20), you will ask a chemist rather than examining mental representations and brain states. That is to say that all the practical work is already done in actual practice and philosophers (at least philosophers of mind) have a tendency to re-invent the wheel in cases like this.