This issue has been discussed previously on the forum.
Here is a newly revised summary of my argument that Hayek overlooked the implications of his own ideas as expressed in “Economics and Knowledge” and “The Facts of the Social Sciences.”
Mises, Hayek, and the A Priorism of the Market: Why Mises was right
Mises and Hayek disagreed about the nature of market theory:
What I see only now clearly is the problem of my relation to Mises, which began with my 1937 article on the economics of knowledge, which was an attempt to persuade Mises himself that when he asserted that the market theory was a priori, he was wrong; that what was a priori was only the logic of individual action, but the moment that you passed from this to the interaction of many people, you entered into the empirical field.(Hayek on Hayek, p.72)(emphasis added)
Hayek is referring to his essay in Individualism and Economic Order, page 35:
I have long felt that the concept of equilibrium itself and the methods which we employ in pure analysis have a clear meaning only when confined to the analysis of a single person and that we are really passing into a different sphere and silently introducing a new element of altogether different character when we apply it to the explanation of the interactions of a number of different individuals.(emphasis added)
Here Hayek makes a distinction between the market (an interaction of a number of people) and the logic of individual action. Hayek agrees that the logic of individual action is a priori, but he argues that market theory is empirical, and that Mises was wrong to believe that market theory is a priori.
To understand the issue involved, and to see how Hayek overlooked the implications of his own ideas, we have to consider two essays from his book Individualism and Economic Order: “Economics and Knowledge” and “The Facts of the Social Sciences.”
In “The Facts of the Social Sciences,” Hayek outlines his concept of the Pure Logic of Choice:
From the fact that…we have to define both the objects of human activity and the different kinds of actions themselves, not in physical terms but in terms of the opinions or intentions of the acting persons, there follow some very important consequences…we can, from the concepts of the objects, analytically conclude something about what the actions will be. If we define an object in terms of a person’s attitude toward it, it follows, of course that the definition of the object implies a statement about the attitude of the person toward the thing. When we say that a person possesses food or money, or that he utters a word, we imply that he knows that the first can be eaten, the second can be used to buy something with, and that the third can be understood—and perhaps many other things.(emphasis added)
Here, Hayek is describing how he conceives of the Pure Logic of Choice. In social science, it is not the physical characteristics of an object that give that object social meaning, but rather the attitude of the acting person toward that thing.
Hayek indicates how this analytic method applies. The attitude a person takes toward an object has a hidden implication. We can analytically conclude something about a person’s action(s) based on that person’s opinion or attitude about the object before him. As Hayek writes:
When we say that a person possesses food or money, or that he utters a word, we imply that he knows that the first can be eaten, the second can be used to buy something with, and that the third can be understood—and perhaps many other things.
This is the Pure Logic of Choice which according to Hayek is:
…the system of tautologies—those series of propositions which are necessarily true because they are merely transformations of the assumptions from which we start.
Hayek argues in “The Facts of the Social Sciences” that it is not the physical properties of a thing that make it an object of the social sciences, but rather the attitude a person takes toward a thing.
Further, once a person takes an attitude toward a thing, his attitude, belief, or opinion, entails further necessary implications which we can analyze and from which we can draw further conclusions. These analytical conclusions are the exact laws (Menger), a priori propositions (Mises), or necessary truths, as Hayek refers to them. Exact laws, a priori propositions, and necessary truths, are, respectively, the focus of theoretical exact science, praxeology, and the Pure Logic of Choice.
Hayek has granted that based on what the actor believes is before him (food, money, a word, etc.) we can analytically conclude something else, and these two things taken together constitute a necessary truth (a priori proposition, exact law, etc.).
The question we ask is this:
If the object before an actor is a market, why are there no analytical implications to the actor’s attitude in this case?
Hayek has said that what makes an object a social object is not its physical characteristics. It is the attitude that an actor takes toward something that determines whether an object is a social object:
If we wish, we could say that all these objects are defined not in terms of their “real” properties but in terms of the opinions people hold about them. In short, in the social sciences the things are what people think they are. Money is money, a word is a word, a cosmetic is a cosmetic, if and because somebody thinks they are.
Once an actor takes a certain attitude toward an object, based on this, we can form a necessary truth by analytically concluding what must also be part of the attitude the actor takes.
Hayek also argues that market theory is empirical and not a priori.
But if a market is a social object (social process, social phenomenon, etc.), then according to Hayek, as a social object it cannot be defined in terms of its physical characteristics. A market can only be defined in terms of the attitude of the person(s) concerned. Hayek writes about the “objects of human activity which constantly occur in the social sciences”:
It is easily seen that all these concepts…refer not to some objective properties possessed by the things, or which the observer can find out about them, but to views which some other person holds about the things. These objects cannot even be defined in physical terms, because there is no single physical property which any one member of a class must possess. These concepts are also not merely abstractions of the kind we use in all physical sciences; they abstract from all the physical properties of the things themselves.(emphasis in the original)
If what Hayek writes is true, then a market, as a social object, is to be defined not in terms of its physical properties, but rather in terms of the attitudes or opinions of the persons concerned. In short, a market is a market if and because somebody thinks it is.
If a market is defined in terms of the opinions and attitudes of the persons concerned, then why are there no analytical conclusions we can draw from this particular attitude a person takes? Why can we draw an analytical conclusion (a tautological transformation) from the fact that a person thinks an object is money, a word, or a cosmetic, but not from the fact that a person thinks something is a market?
Why isn’t market theory a priori by virtue of the Pure Logic of Choice when the object before a person is a market, and we draw analytical conclusions (necessary truths) from the actor’s attitude or opinion in this case?
In this sense, by Hayek’s own reasoning, the theory of the market would seem to be a priori not empirical.
The question is whether a nonarbitrary criterion exists for distinguishing those attitudes of an actor from which we can draw analytical conclusions, from those attitudes of an actor from which we cannot draw analytical conclusions. Hayek clearly argues that analytical conclusions can be drawn from the attitude of the actor when the object before the actor is food, money, or a word. But Hayek seems to overlook other kinds of social objects such as markets, language, law, property, etc. If, for example, the market is a social object, then according to Hayek it cannot be defined in terms of its physical properties, but must be defined in terms of the attitudes of the persons concerned. The same principle should hold for language, law, and property, to the extent these are social objects—objects of the social sciences and not objects of the physical sciences.
If things such as markets and property are social objects defined in terms of the opinions of acting persons, then why can no analytical conclusions be drawn from the concepts of these objects, something Hayek claims can be done with respect to the social objects food, money, and words? What principle distinguishes two distinct classes of social objects such that from the conceptions of class A we can draw analytical conclusions, but from the conceptions of class B we cannot draw analytical conclusions?
If Hayek or his supporters cannot provide a principle for distinguishing between these two classes of social objects, then we must assume, based on what Hayek argues in “Economics and Knowledge” and “The Facts of the Social Sciences” that what holds true for one class of social objects holds true for all classes of social objects. If in the Pure Logic of Choice we may draw analytical conclusions from the social concepts food, money, and words, then in the Pure Logic of Choice we may draw analytical conclusions from the social concepts market, language, law, and property.
Absent a nonarbitrary principle that distinguishes two classes of social objects and precludes us from drawing analytical conclusions from one class of concepts, we must conclude that the Pure Logic of Choice applies to the market as it does to other social objects, and in this sense market theory is a priori.