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The Ultimate Foundation of Economic Science
Ludwig von Mises

The Human Mind

3. The A Priori

One does not annul the cognitive significance of the a priori by qualifying it as tautological. A tautology must ex definitione be the tautology—restatement—of something said already previously. If we qualify Euclidian geometry as a hierarchical system of tautologies, we may say: The theorem of Pythagoras is tautological as it expresses merely something that is already implied in the definition of a right-angled triangle.

But the question is: How did we get the first—the basic—proposition of which the second—the derived—proposition is merely a tautology? In the case of the various geometries the answers given today are either (a) by an arbitrary choice or (b) on account of its convenience or suitability. Such an answer cannot be given with regard to the category of action.

Neither can we interpret our concept of action as a precipitate of experience. It makes sense to speak of experience in cases in which also something different from what was experienced in concreto could have possibly been expected before the experience. Experience tells us something we did not know before and could not learn but for having had the experience. But the characteristic feature of a priori knowledge is that we cannot think of the truth of its negation or of something that would be at variance with it. What the a priori expresses is necessarily implied in every proposition concerning the issue in question. It is implied in all our thinking and acting.

If we qualify a concept or a proposition as a priori, we want to say: first, that the negation of what it asserts is unthinkable for the human mind and appears to it as nonsense; secondly, that this a priori concept or proposition is necessarily implied in our mental approach to all the problems concerned, i.e., in our thinking and acting concerning these problems.

The a priori categories are the mental equipment by dint of which man is able to think and to experience and thus to acquire knowledge. Their truth or validity cannot be proved or refuted as can those of a posteriori propositions, because they are precisely the instrument that enables us to distinguish what is true or valid from what is not.

What we know is what the nature or structure of our senses and of our mind makes comprehensible to us. We see reality, not as it "is" and may appear to a perfect being, but only as the quality of our mind and of our senses enables us to see it. Radical empiricism and positivism do not want to admit this. As they describe it, reality writes, as experience, its own story upon the white sheets of the human mind. They admit that our senses are imperfect and do not fully and faithfully reflect reality. But they do not examine the power of the mind to produce, out of the material provided by sensation, an undistorted representation of reality. In dealing with the a priori we are dealing with the mental tools that enable us to experience, to learn, to know, and to act. We are dealing with the mind's power, and this implies that we are dealing with the limits of its power.

We must never forget that our representation of the reality of the universe is conditioned by the structure of our mind as well as of our senses. We cannot preclude the hypothesis that there are features of reality that are hidden to our mental faculties but could be noticed by beings equipped with a more efficient mind and certainly by a perfect being. We must try to become aware of the characteristic features and limitations of our mind in order not to fall prey to the illusion of omniscience.

The positivistic conceit of some of the forerunners of modem positivism manifested itself most blatantly in the dictum: God is a mathematician. How can mortals, equipped with manifestly imperfect senses, claim for their mind the faculty of conceiving the universe in the same way in which the wholly perfect may conceive it? Man cannot analyze essential features of reality without the help provided by the tools of mathematics. But the perfect being?

After all, it is quite supererogatory to waste time upon controversies concerning the a priori. Nobody denies or could deny that no human reasoning and no human search for knowledge could dispense with what these a priori concepts, categories, and propositions tell us. No quibbling can in the least affect the fundamental role played by the category of action for all the problems of the science of man, for praxeology, for economics, and for history.

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