- Thinking is an essential component of human life. We are naturally interested in a systematic study of the activity of thinking. However, on account of its private and ephemeral character, we have come to distrust unaided reflections on our consciousness and to depend more on the study of the accompanying behaviours and the physiology of the brain, which are publicly observable. Recently the use of computational models has been added to these older tools for the study of the mind.
- Indeed, with the rapid development and the increasingly broad application of computers, the traditional problem of mind and matter experiences a revival in the guise of a sharper formulation in terms of computers and computation. It is of both practical and theoretical significance to determine the extent to which thinking is computational. The ambitious general question is to ask whether all thinking is basically computational. Or, to use a familiar but ambiguous formulation: can computers think?
- The central component of what I call computabilism is the position which answers this question affirmatively. When we try, however, to think about the reasons for and against this position, we begin to realize that we are inclined to conflate different questions by using certain natural but hard-to-justify presuppositions. In particular, most people who study the question today tend to assume, without pausing to ask for reasons, some form of physicalism1 or naturalism. More specifically, the common assumption is psychophysiological parallelism in the sense of a one-to-one correlation between mental and physiological phenomena. Consequently, computabilism for the mental is identified with computabilism for brain processes.
- In this essay I shall first try to formulate some problems about the thesis of parallelism and its related conception of (the scope of) science. In any case, regardless of the truth or falsity of the thesis of parallelism, it is helpful to distinguish computabilism for the mental from that for the brain, because the reasons for and against them are of quite different types. In particular, we know at present more about the mind than about the brain.
- Once we make such a distinction, we see that computabilism for the brain is related to the general question about the computational character of physical and biological processes. What is often known as physicalism2 includes both the thesis of psychophysiological parallelism and one of biophysical parallelism, which postulates some sort of reducibility of the biological to the physical. However, for all we know, even if computabilism for the physical is true, it does not follow necessarily that computabilism for the biological is also true.
- We see, therefore, that the position of computabilism involves a number of different problems. I shall here consider some of these problems and shall formulate a few more definite subproblems. I shall present my thoughts under the following four headings:
- Parallelism and the scope of science: can minds do more than brains?
- Computabilism for the brain: is the brain like a computer?
- Computabilism for the physical: is physics algorithmic?
- Computabilism for the mental: is all thinking computational?
- The content of consciousness is available to each of us through our inner experience and our disciplined introspection. There are certainly many conscious processes that are not at present known to be representable in physiological or physical or computational terms. The challenge or the frustrating task is to arrive at a reasonable conjecture as to the truth or falsity of physicalism and computabilism on the basis of what we know, taking into consideration our gross ignorance about the full powers of brains and computers.
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