Reductive Physicalism

Reduction

What is reduction? What does it mean to say that the mind is or is not reducible to the brain? Like many terms, both in and out of philosophy, the word reduction is used in a variety of ways. In everyday language, we often understand reduction, quite naturally, to mean lessening or reducing in size. You might go on a reducing diet—for example, by eliminating those luscious French sauces that require reduction when cooking. In philosophy, the word reduction is sometimes used with this ordinary meaning, as philosophers often take it to mean simplification. When we reduce one ontological category to another, by showing the one category [Page 637]to be nothing but the other, we simplify our ontology by cutting down the number of kinds of things that exist in the world. However, the philosophical notion of reduction can also encompass an explanatory element. One category reduces to another, in this sense, if can be explained in terms of the other.

In philosophy of mind, these two notions of reduction—the nothing but notion and the explanatory notion—often (though, as we'll see, not always) overlap. For example, one way in which the mind can be understood as nothing but the brain (or, more accurately, certain parts of the brain) is by reductively explaining mental processes entirely in terms of the neural processes. Not all explanations of one thing in terms of something else are reductive explanations. I might explain the reason for the spill on the floor in terms of why it happened: My cat jumped on the table. But reductive explanations are not like this, they do not tell us the cause of something; rather, they aim to tell us what something is. For example, genetic material is reductively explained in terms of DNA, water in terms of H2O, temperature in a gas in terms of mean molecular momentum, and if the mental is reductively explainable in terms of neural processes, mental processes in terms of neural ones. For example, one version of reductive physicalism holds that pain is reducible to C-fiber activity (or, more accurately, to whatever neural process that is found to be perfectly correlated with pain). Such a reduction aims to explain pain by showing that it is nothing but C-fiber activity. If pain could be entirely explained in terms of processes in the brain, such as C-fiber activity, we would have both simplified our ontology and found out what pain really is.

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