Brain Bisection and the Unity of Consciousness
Nagel (Thomas)
Source: Nagel (Thomas) - Mortal Questions
Paper - Abstract

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Introduction (Full Text)

  1. There has been considerable optimism recently, among philosophers and neuroscientists, concerning the prospect for major discoveries about the neurophysiological basis of mind. The support for this optimism has been extremely abstract and general. I wish to present some grounds for pessimism. That type of self-understanding may encounter limits which have not been generally foreseen: the personal, mentalist idea of human beings may resist the sort of coordination with an understanding of humans as physical systems, that would be necessary to yield anything describable as an understanding of the physical basis of mind. I shall not consider what alternatives will be open to us if we should encounter such limits. I shall try to present grounds for believing that the limits may exist - grounds derived from extensive data now available about the interaction between the two halves of the cerebral cortex, and about what happens when they are disconnected. The feature of the mentalist conception of persons which may be recalcitrant to integration with these data is not a trivial or peripheral one, that might easily be abandoned. It is the idea of a single person, a single subject of experience and action, that is in difficulties. The difficulties may be surmountable in ways I have not foreseen. On the other hand, this may be only the first of many dead ends that will emerge as we seek a physiological understanding of the mind.
  2. To seek the physical basis or realization of features of the phenomenal world is in many areas a profitable first line of inquiry, and it is the line encouraged, for the case of mental phenomena, by those who look forward to some variety of empirical reduction of mind to brain, through an identity theory, a functionalist theory, or some other device. When physical reductionism is attempted for a phenomenal feature of the external world, the results are sometimes very successful, and can be pushed to deeper and deeper levels. If, on the other hand, they are not entirely successful, and certain features of the phenomenal picture remain unexplained by a physical reduction, then we can set those features aside as purely phenomenal, and postpone our understanding of them to the time when our knowledge of the physical basis of mind and perception will have advanced sufficiently to supply it. (An example of this might be the moon illusion, or other sensory illusions which have no discoverable basis in the objects perceived.) However, if we encounter the same kind of difficulty in exploring the physical basis of the phenomena of the mind itself, we cannot adopt the same line of retreat. That is, if a phenomenal feature of mind is left unaccounted for by the physical theory, we cannot postpone the understanding of it to the time when we study the mind itself - for that is exactly what we are supposed to be doing. To defer to an understanding of the basis of mind which lies beyond the study of the physical realization of certain aspects of it is to admit the irreducibility of the mental to the physical. A clearcut version of this admission would be some kind of dualism. But if one is reluctant to take such a route, then it is not clear what one should do about central features of the mentalistic idea of persons which resist assimilation to an understanding of human beings as physical system. It may be true of some of these features that we can neither find an objective basis for them, nor give them up. It may be impossible for us to abandon certain ways of conceiving and representing ourselves, no matter how little support they get from scientific research. This, I suspect, is true of the idea of the unity of a person: an idea whose validity may be called into question with the help of recent discoveries about the functional duality of the cerebral cortex. It will be useful to present those results here in outline.

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