Joseph Weizenbaum , Computer Power and Human Reason (New York, W.H. Freeman and Company, 1976), pp 221-22.
There was a time when physics dreamed of explaining the whole of physical reality in terms of one comprehensive formalism. Leibnitz taught that if we knew the position and velocity of every elementary particle in the universe, we could predict the universe’s whole future course. But then Werner Heisenberg proved that the very instruments man must use in order to measure physical phenomena disturb those phenomena, and that it is therefore impossible in principle to know both the exact position and the velocity of even a single elementary particle. He did not thereby falsify Leibnitz’s conjecture. But he did show that its major premise was unattainable. That, of course, was sufficient to shatter the Leibnitzian dream. Only a little later, Kurt Godel exposed the shakiness of the foundations of mathematics and logic itself by proving that every interesting formal system has some statements whose truth or falsity cannot be decided by the formal means of the system itself, in other words, that mathematics must necessarily be forever incomplete. It follows from this and others of Godel’s results that “The human mind is incapable of formulating (or mechanizing) all its mathematical intuitions. I.e. if it has succeeded in formulating some of them, this very fact yields new intuitive knowledge.” [i]
Both Heisenberg’s so-called uncertainty principle and Godel’s incompleteness theorem sent terrible shock-waves through the worlds of physics, mathematics, and philosophy of science. But no one stopped working. Physicists, mathematicians, and philosophers more or less gracefully accepted the undeniable truth that there are limits to how far the world can be comprehended in Leibnitzian terms alone.
Much too much has already been made of the presumed implications of Heisenberg’s and Godel’s results for artificial intelligence. I do not wish to contribute to that discussion here. But there is a sense in which psychology and artificial intelligence may usefully follow the example of the new-found humility of modern mathematics and physics: they should recognize that “while the constraints and limitations of logic do not exert their force on the things of the world, they do constrain and limit was are to count as defensible descriptions and interpretations of things.” [ii] Were they to recognize that, they could then take the next liberating step of also recognizing that truth is not equivalent to formal provability.
The lesson I have tried to teach here is not that the human mind is subject to Heisenberg uncertainties – though it may be – and that we can therefore never wholly comprehend it in terms of the kinds of reduction to discrete phenomena Leibniz had in mind. The lesson here is rather that the part of the human mind which communicates to us in rational and scientific terms is itself an instrument that disturbs what it observes, particularly its voiceless partner, the unconscious, between which and our conscious selves it mediates. Its constraints and limitations circumscribe what are to constitute rational – again, if you will, scientific – descriptions and interpretations of the things of the world. These descriptions can therefore never be whole, anymore than a musical score can be a whole description or interpretation of even the simplest song.
But, and this is the saving grace of which an insolent and arrogant scientism attempts to rob us, we come to know and understand not only by way of the mechanisms of the conscious. We are capable of listening with the third ear, of sensing living truth that is truth beyond any standards of provability. It is that kind of understanding, and the kind of intelligence that is derived from it, which I claim is beyond the abilities of computers to simulate.
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[1] H. Wang, From Mathematics to Philosophy ( New York: Humanities Press, 1974), p. 324.
[1] D.C. Denett, “The Abilities of Men and Machines.” Paper delivered to the American Philosophical Association, December 29, 1970.
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Joseph Weizenbaum is Professor of Computer Science at MIT. He composed SLIP, a list-processing language , and ELIZA, a natural-language processing system. He is a Fellow of the American Association for the Advancement of Science, and a Fellow of the Center for Advanced Study in the Behavioral Sciences, Stanford, California (1973) . He received his higher education at Wayne State University.
for Platonic Realism and the Concept of Mind, click here:
On the Connection between Godel’s Theorem and Psak, click here:
