If minds are brains, we just do not need the hypothesis that they are souls too. Dualist explanations
are inherently less simple than materialist ones, as they posit the existence of two kinds of things
rather than one. Simplicity is not a virtue all by itself, as we see in the hypothesis of the first great
philosopher-scientist, Thales, that everything is water. Einstein said that everything should be as
simple as possible but not simpler, and Thales' hypothesis is just too simple, as was Aristotle's
somewhat more complicated story that the four fundamental elements include earth, air, and fire as
well as water. Modern chemistry sees the need to consider more than a hundred elements, including
hydrogen and oxygen, which combine to produce water. Similarly, it is possible that there could be
phenomena that require explanations invoking soul or spirit in addition to matter and energy.
However, the rapidly progressing development of neuroscientific explanations of many mental
phenomena suggests that souls are no more part of our best general explanatory account than is
caloric, which was thought to be the substance of heat before the advent of the theory that heat is just
molecular motion.
Sufficient evidence has been presented in this chapter to justify using mind-brain identity as the
basis for the rest of the book's discussion of the nature of knowledge, reality, morality, and meaning.
Figure 3.3 shows the overall structure of the inference to the best explanation that minds are brains,
including the kinds of evidence that are increasingly being accounted for in terms of neural
mechanisms. The hypothesis that minds are brains competes with the hypothesis that minds are souls,
whose explanatory successes are few. The figure also shows competition between the higher-level
hypothesis that minds evolved naturally and the hypothesis that minds arise from divine creation. If
you are convinced by my argument that minds are brains, then proceed to Chapter 4. For the sake,
however, of philosophical skeptics about mind-brain identity, I will close this chapter with a
discussion of some of the most influential objections to it.
3.3 Structure of the inference that mind-body identity is the best available explanation of many psychological phenomena. Explanations
are indicated by solid lines, and competition between hypotheses by dotted lines.
Objections to Mind-Brain Identity
For most people, the immediate objection to the claim that minds are brains is that it conflicts with
their religious beliefs about immortality. Their faith says that God created souls that can survive the
death of their bodies. But I argued earlier in this chapter that there is no good evidence for
immortality, and in the previous chapter I showed why evidence provides a better way of justifying
beliefs than does faith. Another sweeping rejection of my approach would be the postmodernist
charge that I dogmatically ignore the philosophical view currently dominant in cultural studies that the
world is just a text and that science is just one of many equally good ways of talking about it. My
defense of evidence over faith in Chapter 2 is one part of a response to this view, and a further
response will be found in Chapter 4's discussion of the nature of reality and its independence of mind.
Mind-brain identity often seems intuitively implausible even to nonreligious people, because the
conceptual schemes that we acquire from our cultures are inherently dualist. Languages from Hebrew
to Greek to English have terms for mind and spirit that seem to designate nonphysical entities.
Children learn from their parents to see their thoughts and feelings as intrinsically different from the
states of their bodies. People's conscious experiences strongly suggest to them that their minds are
making free choices independent of biological causes. The Brain Revolution requires a major
conceptual shift to reclassify states of mind as neural.
Some philosophers have used such dualist intuitions to challenge mind-brain identity through
thought experiments. The most prevalent is the “zombie” argument, which goes like this. Imagine
people who are just like us in all physical respects but differ only in that they lack consciousness.
Call them zombies, although they are not like the fearsome zombies of horror movies. Such people are
clearly conceivable—just think of anyone you know and imagine that he or she is not really conscious
but only seems to be. Because we can imagine beings that are physically identical to us but lack
conscious experience, conscious minds are not necessarily identical to brains. But for an identity