Here are excerpts from Ed Feser’s essay.
In late 1952, F. A. Hayek sent his friend Karl Popper a copy of his recently published book The Sensory Order: An Inquiry into the Foundations of Theoretical Psychology. In a letter dated December 2, 1952, Popper acknowledged receipt of the book and responded as follows to what he had read in it:
I am not sure whether one could describe your theory as a causal theory of the sensory order. I think, indeed, that one can. But then, it would be also the sketch of a causal theory of the mind. But I think I can show that a causal theory of the mind cannot be true (although I cannot show this of the sensory order; more precisely, I think I can show the impossibility of a causal theory of the human language (although I cannot show the impossibility of a causal theory of perception). I am writing a paper on the impossibility of a causal theory of the human language, and its bearing upon the body-mind problem, which must be finished in ten days. I shall send you a copy as soon as it is & typed.
In a later letter dated January 19, 1953, Popper added, As to my comments on your book, they are, as far as criticism is concerned, implicit in my paper. I think you have made a splendid effort towards a theory of the sub-linguistic (¼ sub-human ((¼descriptive)) language) level of mind; but I believe that no physiological approach (although most important) can be sufficient to explain the descriptive and argumentative functions of language. Or in other words, there can be no causal or physiological theory of reason. The paper Popper was referring to is his short article ‘‘Language and the body-mind problem.’’ Hayek began a draft of a paper entitled ‘‘Within systems and about systems: A statement of some problems of a theory of communication,’’ which, as Jack Birner has suggested, appears to have been intended at least in part as a response to Popper’s criticisms. But it was never completed, and Hayek never addressed Popper’s arguments in any of his published work. The Sensory Order has, however unjustly, largely been forgotten outside the circles of Hayek specialists. Popper’s brief paper is perhaps even less well known. Neither Popper’s letters to Hayek nor Hayek’s unfinished draft have yet been published. So, this episode might seem rather insignificant in the history of thought and indeed of little significance even to our understanding of either Hayek’s thought or Popper’s. But, as I hope to show in what follows, nothing could be further from the truth. With respect both to its general themes and to some of the specific philosophical moves made by each side, the brief, private dispute between Hayek and Popper foreshadowed a more prominent debate within twentieth-century analytic philosophy that began in the 1970s and continues to this day. Moreover, both the dispute between Hayek and Popper and the later debate reflect a deep tension that has lain at the heart of Western thought since the time of the scientific revolution. On the one hand, there is the ‘‘mechanical world picture’’ according to which all natural phenomena can be explained entirely in terms of the mathematically describable behavior of matter in motion. On the other hand, there are rational human thought processes, including the philosophical and scientific theorizing that led to the mechanical world picture itself. It is far from obvious that the latter can be fitted comfortably into the former – that human rationality can be explained in terms of purely material processes – and from the time of Descartes until relatively recently, the dominant view was that it could not be. Hayek and Popper were writing at a time when this view began to give way to a new materialist orthodoxy. Hayek, though arguably more sensitive to the tension in question than most contemporary materialists, nevertheless thought it could be resolved in a way favorable to a broadly materialist or ‘‘naturalistic’’ understanding of the mind. Popper disagreed and believed the older, dualistic conception of the mind to be essentially correct, and as we will see, his reasons for doing so have in more recent years been regarded even by some non-dualist philosophers as posing a serious difficulty for materialism. In the next section, I will set the stage for the discussion of Hayek and Popper with a brief account of the nature and origins of the mind-body problem (or ‘‘body-mind problem,’’ as Popper preferred to call it). We will see that there are really at least three mind-body problems, and that while Hayek and most contemporary philosophers focus on the first of these, Popper was more concerned with the other two and believed that they pose a more serious difficulty for materialism than the former does. The third section will explain what a ‘‘causal theory of the mind’’ is and the respects in which Hayek’s account can be regarded as a causal theory. The fourth section will examine Popper’s main criticism of causal theories, which will be elucidated by comparison with the views of contemporary philosopher Hilary Putnam, who (apparently independently) developed a line of argument that parallels and extends the one presented by Popper. Finally, in the fifth section, I will consider the possible response to Popper suggested both by Hayek’s unpublished draft and by things Hayek had to say in some of his published work, relating it to the responses contemporary philosophers have given to arguments like those presented by Popper and Putnam. I will argue that none of these replies succeeds and that the Popperian critique remains a powerful and as yet unanswered challenge not only to dogmatic materialism but even to the more modest and critical form of materialism or naturalism defended by Hayek.
Hayek’s unfinished draft ‘‘Within Systems and About Systems’’ is a study of this problem and, as noted earlier, seems intended at least in part as a response to the difficulties raised by Popper. While he does not explicitly present it as such, he does say that he intends to reply to those who regard it as ‘‘futile’’ or ‘‘absurd’’ to analyze mental processes in terms of ‘‘causal systems,’’ and that of the various mental phenomena his focus will be on ‘‘communication and particularly description’’ – the latter being precisely one of the phenomena Popper said could not be explained causally.26 Moreover, he explicitly cites Buhler’s distinction between functions of language, which Popper had borrowed and adapted for the purposes of his own argument. Hayek’s central claim is that: [F]or any causal system there is a limit to the complexity of other systems for which the former can provide the analogon of a description or explanation, and that this limit necessarily excludes the possibility of a system ever describing or explaining itself. This means that, if the human mind were a causal system, we would necessarily experience in discussing it precisely those obstacles and difficulties which we do encounter and which are often regarded as proof that the human mind is not a causal system. The impossibility of the mind’s fully explaining itself is a recurring theme in Hayek’s writings on our subject. He takes it to follow from the complexity of any system capable of exhibiting mental properties, and in particular from the potentially infinite regress entailed by the mind’s reflection on its own operations. For when one group of mental operations becomes an object of thought for another, understanding the latter will in turn require that it be made an object of thought for yet another, and so on ad infinitum, as each meta-level of thought becomes an object-level for another meta-level. The parallel with Godel’s incompleteness theorems, Cantor’s set theory, and Russell’s theory of types is obvious, and Hayek took puzzles of self-referentiality of the sort studied by such thinkers to provide the key to understanding why a material mind should seem to us to be inexplicable in material terms. The trouble with this sort of move, considered as a reply to Popper, is that it assumes that it is the ‘‘self’’ in self-referentiality that is the problem, when in fact it is the ‘‘referentiality’’ that is. Once we have a system capable of referring at all – capable, that is, of intentionality or representation – then yes, puzzles of self-referentiality are going to arise if the system becomes sufficiently complex. But the question Popper is addressing is not whether a complex system already capable of intentionality can understand itself. The question he is addressing is whether a purely material system could exhibit intentionality of even a rudimentary, non-self-referential sort merely by virtue of bearing certain causal relations to other objects and events. Systems of the sort studied by Godel, Cantor, and Russell are completely irrelevant to this question, as should be obvious when we consider that these systems already presuppose the existence of intentionality insofar as they presuppose minds capable of interpreting otherwise meaningless physical marks as symbols of logic and set theory. What we need to know is how such intentionality enters the picture in the first place. That Hayek does not clearly understand what is at issue is evident from what he says in ‘‘Within Systems and About Systems.’’ Much of the draft recapitulates the theory of The Sensory Order, and like the book makes free use of terms like ‘‘classification,’’ ‘‘representation,’’ ‘‘models,’’ and ‘‘map’’ – terms the intentional connotations of which are precisely what need to be grounded. To be sure, Hayek says that he intends to explain ‘‘the property to which we refer by such terms as ‘intention,’ ‘purpose,’ ‘aim,’ ‘need,’ or ‘desire’’’ and acknowledges that ‘‘we must not use any of these ‘mental’ terms until we have succeeded in adequately defining them in terms of our causal system.’’