A fashionable tendency in contemporary philosophy is to deny the existence of any a priori knowledge. All human knowledge, it is contended, is derived from experience. This attitude can easily be understood as an excessive reaction against the extravagances of theology and a spurious philosophy of history and of nature. Metaphysicians were eager to discover by intuition moral precepts, the meaning of historical evolution, the properties of soul and matter, and the laws governing physical, chemical, and physiological events. Their volatile speculations manifested a blithe disregard for matter-of-fact knowledge. They were convinced that, without reference to experience, reason could explain all things and answer all questions.
The modern natural sciences owe their success to the method of observation and experiment. There is no doubt that empiricism and pragmatism are right as far as they merely describe the procedures of the natural sciences. But it is no less certain that they are entirely wrong in their endeavors to reject any kind of a priori knowledge and to characterize logic, mathematics, and praxeology either as empirical and experimental disciplines or as mere tautologies.
With regard to praxeology the errors of the philosophers are due [p. 33] to their complete ignorance of economics  and very often to their shockingly insufficient knowledge of history. In the eyes of the philosopher the treatment of philosophical issues is a sublime and noble vocation which must not be put upon the low level of other gainful employments. The professor resents the fact that he derives an income from philosophizing; he is offended by the thought that he earns money like the artisan and the farm hand. Monetary matters are mean things, and the philosopher investigating the eminent problems of truth and absolute eternal values should not soil his mind by paying attention to problems of economics.
The problem of whether there are or whether there are not a priori elements of thought--i.e., necessary and ineluctable intellectual conditions of thinking, anterior to any actual instance of conception and experience--must not be confused with the genetic problem of how man acquired his characteristically human mental ability. Man is descended from nonhuman ancestors who lacked this ability. These ancestors were endowed with some potentiality which in the course of ages of evolution converted them into reasonable beings. This transformation was achieved by the influence of a changing cosmic environment operating upon succeeding generations. Hence the empiricist concludes that the fundamental principles of reasoning are an outcome of experience and represent an adaptation of man to the conditions of his environment.
This idea leads, when consistently followed, to the further conclusion that there were between our prehuman ancestors and homo sapiens various intermediate stages. There were beings which, although not yet equipped with the human faculty of reason, were endowed with some rudimentary elements of ratiocination. Theirs was not yet a logical mind, but a prelogical (or rather imperfectly logical) mind. Their desultory and defective logical functions evolved step by step from the prelogical state toward the logical state. Reason, intellect, and logic are historical phenomena. There is a history of logic as there is a history of technology. Nothing suggests that logic as we know it is the last and final stage of intellectual evolution. Human logic is a historical phase between prehuman nonlogic on the one [p. 34] hand and superhuman logic on the other hand. Reason and mind, the human beings' most efficacious equipment in their struggle for survival, are embedded in the continuous flow of zoological events. They are neither eternal nor unchangeable. They are transitory.
Furthermore, there is no doubt that every human being repeats in his personal evolution not only the physiological metamorphosis from a simple cell into a highly complicated mammal organism but no less the spiritual metamorphosis from a purely vegetative and animal existence into a reasonable mind. This transformation is not completed in the prenatal life of the embryo, but only later when the newborn child step by step awakens to human consciousness. Thus every man in his early youth, starting from the depths of darkness, proceeds through various states of the mind's logical structure.
Then there is the case of the animals. We are fully aware of the unbridgeable gulf separating our reason from the reactive processes of their brains and nerves. But at the same time we divine that forces are desperately struggling in them toward the light of comprehension. They are like prisoners anxious to break out from the doom of eternal darkness and inescapable automatism. We feel with them because we ourselves are in a similar position: pressing in vain against the limitation of our intellectual apparatus, striving unavailingly after unattainable perfect cognition.
But the problem of the a priori is of a different character. It does not deal with the problem of how consciousness and reason have emerged. It refers to the essential and necessary character of the logical structure of the human mind.
The fundamental logical relations are not subject to proof or disproof. Every attempt to prove them must presuppose their validity. It is impossible to explain them to a being who would not possess them on his own account. Efforts to define them according to the rules of definition must fail. They are primary propositions antecedent to any nominal or real definition. They are ultimate unanalyzable categories. The human mind is utterly incapable of imagining logical categories at variance with them. No matter how they may appear to superhuman beings, they are for man inescapable and absolutely necessary. They are the indispensable prerequisite of perception, apperception, and experience.
They are no less an indispensable prerequisite of memory. There is a tendency in the natural sciences to describe memory as an instance of a more general phenomenon. Every living organism conserves the effects of earlier stimulation, and the present state of inorganic [p. 35] matter is shaped by the effects of all the influences to which it was exposed in the past. The present state of the universe is the product of its past. We may, therefore, in a loose metaphorical sense, say that the geological structure of our globe conserves the memory of all earlier cosmic changes, and that a man's body is the sedimentation of his ancestors' and his own destinies and vicissitudes. But memory is something entirely different from the fact of the structural unity and continuity of cosmic evolution. It is a phenomenon of consciousness and as such conditioned by the logical a priori. Psychologists have been puzzled by the fact that man does not remember anything from the time of his existence as an embryo and as a suckling. Freud tried to explain this absence of recollection as brought about by suppression of undesired reminiscences. The truth is that there is nothing to be remembered of unconscious states. Animal automatism and unconscious response to physiological stimulations are neither for embryos and sucklings nor for adults material for remembrance. Only conscious states can be remembered.
The human mind is not a tabula rasa on which the external events write their own history. It is equipped with a set of tools for grasping reality. Man acquired these tools, i.e., the logical structure of his mind, in the course of his evolution from an amoeba to his present state. But these tools are logically prior to any experience.
Man is not only an animal totally subject to the stimuli unavoidably determining the circumstances of his life. He is also an acting being. And the category of action is logically antecedent to any concrete act.
The fact that man does not have the creative power to imagine categories at variance with the fundamental logical relations and with the principles of causality and teleology enjoins upon us what may be called methodological apriorism.
Everybody in his daily behavior again and again bears witness to the immutability and universality of the categories of thought and action. He who addresses fellow men, who wants to inform and convince them, who asks questions and answers other people's questions, can proceed in this way only because he can appeal to something common to all men--namely, the logical structure of human reason. The idea that A could at the same time be non-A or that to prefer
A to B could at the same time be to prefer B to A is simply inconceivable and absurd to a human mind. We are not in the position to comprehend any kind of prelogical or metalogical thinking. We cannot think of a world without causality and teleogy.
It does not matter for man whether or not beyond the sphere accessible [p. 36] to the human mind there are other spheres in which there is something categorially different from human thinking and acting. No knowledge from such spheres penetrates to the human mind. It is idle to ask whether things-in-themselves are different from what they appear to us, and whether there are worlds which we cannot divine and ideas which we cannot comprehend. These are problems beyond the scope of human cognition. Human knowledge is conditioned by the structure of the human mind. If it chooses human action as the subject matter of its inquiries, it cannot mean anything else than the categories of action which are proper to the human mind and are its projection into the external world of becoming and change. All the theorems of praxeology refer only to these categories of action and are valid only in the orbit of their operation. They do not pretend to convey any information about never dreamed of and unimaginable worlds and relations.
Thus praxeology is human in a double sense. It is human because it claims for its theorems, within the sphere precisely defined in the underlying assumptions, universal validity for all human action. It is human moreover because it deals only with human action and does not aspire to know anything about nonhuman--whether subhuman or superhuman--action.
The Alleged Logical Heterogeneity of Primitive Man
It is a general fallacy to believe that the writings of Lucien Levy-Bruhl give support to the doctrine that the logical structure of mind of primitive man was and is categorially different from that of civilized man. On the contrary, what Levy-Bruhl, on the basis of a careful scrutiny of the entire ethnological material available, reports about the mental functions of primitive man proves clearly that the fundamental logical relations and the categories of thought and action play in the intellectual activities of savages the same role they play in our own life. The content of primitive man's thoughts differs from the content of our thoughts, but the formal and logical structure is common to both.
It is true that Levy-Bruhl himself maintains that the mentality of primitive peoples is essentially "mystic and prelogical" in character; primitive man's collective representations are regulated by the "law of participation" and are consequently indifferent to the law of contradiction. However, Levy-Bruhl's distinction between prelogical and logical thinking refers to the content and not to the form and categorial structure of thinking. For he declares that also among peoples like ourselves ideas and relations between ideas governed by the "law of participation" exist, more or less independently, more or less impaired, but yet ineradicable, side by side, with those subject to the [p. 37] law of reasoning. "The prelogical and the mystic are co-existent with the logical" 
Levy-Bruhl relegates the essential teachings of Christianity to the realm of the prelogical mind. Now, many objections can possibly be raised and have been raised against the Christian doctrines and their interpretation by theology. But nobody ever ventured to contend that the Christian fathers and philosophers--among them St. Augustine and St. Thomas--had minds whose logical structure was categorially different from that of our contemporaries. The dispute between a man who believes in miracles and another who does not refers to the content of thought, not to its logical form. A man who tries to demonstrate the possibility and reality of miracles may err. But to unmask his error is --as the brilliant essays of Hume and Mill show--Certainly no less logically intricate than to explode any philosophical or economic fallacy.
Explorers and missionaries report that in Africa and Polynesia primitive man stops short at his earliest perception of things and never reasons if he can in any way avoid it. European and American educators sometimes report the same of their students. With regard to the Mossi on the Niger Levy-Bruhl quotes a missionary's observation: "Conversation with them turns only upon women, food, and (in the rainy season) the crops." What other subjects did many contemporaries and neighbors of Newton, Kant, and Levy-Bruhl prefer?
The conclusion to be drawn from Levy-Bruhl's studies is best expressed in his own words: "The primitive mind, like our own, is anxious to find the reasons for what happens, but it does not seek these in the same direction as we do."
A peasant eager to get a rich crop may--according to the content of his ideas--choose various methods. He may perform some magical rites, he may embark upon a pilgrimage, he may offer a candle to the image of his patron saint, or he may employ more and better fertilizer. But whatever he does, it is always action, i.e., the employment of means for the attainment of ends. Magic is in a broader sense a variety of technology. Exorcism is a deliberate purposeful action based on a world view which most of our contemporaries condemn as superstitious and therefore as inappropriate. But the concept of action does not imply that the action is guided by a correct theory and a technology promising success and that it attains the end aimed at. It only implies that the performer of the action believes that the means applied will produce the desired effect. [p. 38]
No facts provided by ethnology or history contradict the assertion that the logical structure of mind is uniform with all men of all races, ages, and countries.
 Hardly any philosopher had a more universal familiarity with various
branches of contemporary knowledge than Bergson. Yet a casual remark in his last great book clearly
proves that Bergson was completely ignorant of the fundamental theorem of the modern theory
of value and exchange. Speaking of exchange he remarks "l'on ne peut le pratiquer sans s'être
demandé si les deux objets échangés sont bien de même valeur, c'est-à-die échangeables contre un même
troisième." (Les Deux Sources de law morale et de la religion [Paris, 1932], p. 68.)
 Lévy-Bruhl, How Natives Think, trans. by L.A. Clare (New York, 1932), p. 386.
 Ibid., p. 377.
 Lévy-Bruhl, Primitive Mentality, trans. by L.A. Clare (New York, 1923), pp. 27-29.
 Ibid., p. 27.
 Ibid., p. 437.
 Cf. the brilliant statements of Ernst Cassirer, Philosophie der symbolischen Formen
(Berlin, 1925), II, 78.