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The behaviour of the split-brain patients is odd, and it is tempting to suppose that we are confronted with one body and two minds. This temptation is enhanced by the physical separation of the hemispheres. Commissurotomy, however, is a modern operation and people have for centuries speculated that the mind is not an indissoluble unity. Plato in The Republic suggests that the soul is divided into three faculties: roughly speaking, reason, appetite and passion. His argument for this is that we are subject to internal conflict. A person may be thirsty and yet unwilling to drink. Rather than say that one person is the subject of incompatible predicates – that Glaucon, say, both wants to drink and does not want to drink – Plato concludes that Glaucon is not a unity. Glaucon's appetite wants to drink, his reason does not want to drink. Reason and appetite, though possibly different faculties, are not likely candidates for mindhood. One's appetites enter into one's calculations and may be unruly, but there is no temptation to think that they constitute a thinking rational agent in their own right. A mind must be more than just, say, appetite. Certain kinds of irrationality, on the other hand, encourage the speculation that a person may comprise more than one centre of agency. Self-deception, in particular, if it exists in its most extreme and paradoxical form, may only be coherently explicable by supposing that the mind is not a unity. It may be that the parts into which the mind is split in order to explain self-deception must themselves be regarded as minds.

DOI: 10.1007/978-1-349-23178-2_8

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