No thinking and no acting would be possible to man if the universe were chaotic, i.e., if there were no regularity whatever in the succession and concatenation of events. In such a world of unlimited contingency nothing could be perceived but ceaseless kaleidoscopic change. There would be no possibility for man to expect anything. All experience would be merely historical, the record of what has happened in the past. No inference from past events to what might happen in the future would be permissible. Therefore man could not act.

Reasoning is necessarily always deductive. This was implicitly admitted by all the attempts to justify ampliative induction by demonstrating or proving its logical legitimacy, i.e., by providing a deductive interpretation of induction. The plight of empiricism consists precisely in its failure to explain satisfactorily how it is possible to infer from observed facts something concerning facts yet unobserved.

Empiricism proclaims that experience is the only source of human knowledge and rejects as a metaphysical prepossession the idea that all experience presupposes a priori categories. But starting from its empiricistic approach, it postulates the possibility of events that have never been experienced by any man.

Determinism must be clearly distinguished from materialism. Materialism declares that the only factors producing change are those that are accessible to investigation by the methods of the natural sciences. It does not necessarily deny the fact that human ideas, judgments of value, and volitions are real too and can produce definite changes. But as far as it does not deny this, it asserts that these “ideal” factors are the inevitable result of external events that necessarily beget in the bodily structure of men definite reactions.

The insurmountable difficulties that any materialistic interpretation of reality encounters can be shown in an analysis of the most popular materialistic philosophy, Marxian dialectical materialism.

All the elements of the theoretical sciences of human action are already implied in the category of action and have to be made explicit by expounding its contents. As among these elements of teleology is also the category of causality, the category of action is the fundamental category of epistemology, the starting point of any epistemological analysis.

The concepts of natural selection and evolution make it possible to develop a hypothesis about the emergence of the logical structure of the human mind and the a priori.

Animals are driven by impulses and instincts. Natural selection eliminated those specimens and species which developed instincts that were a liability in the struggle for survival. Only those endowed with impulses serviceable to their preservation survived and could propagate their species.

From the praxeological point of view it is not possible to question the real existence of matter, of physical objects and of the external world. Their reality is revealed by the fact that man is not omnipotent. There is in the world something that offers resistance to the realization of his wishes and desires. Any attempt to remove by a mere fiat what annoys him and to substitute a state of affairs that suits him better for a state of affairs that suits him less is vain.

Action is a category that the natural sciences do not take into account. The scientist acts in embarking upon his research work, but in the orbit of natural events of the external world which he explores there is no such thing as action. There is agitation, there is stimulus and response, and, whatever some philosophers may object, there is cause and effect. There is what appears to be an inexorable regularity in the concatenation and sequence of phenomena. There are constant relations between entities that enable the scientist to establish the process called measurement.