Karl Popper held an opposition to determinism, based mainly in his political and ethical convictions. Nevertheless, most of his reflections upon it belong to epistemology. This paper studies Popper's refutation of determinism and his three main arguments of a priori nature against it. Some attention is paid also to the Popperian interpretation of quantic mechanical indeterminism.

Throughout the centuries, the studious of the nature have verified time and time again the effectiveness of the mathematics to formalize the knowledge of the world. To what extent it is thus, and why reason, they are enigmas that still wait for answer. Some theoretical alternatives are explored to catch the diverse dimensions of this subject.

Arguments on determinism and fate must be placed in human being's industry to over come life uncertainties. For a long time was regarded suitable to postulate an ontologi cal necessity to progress towards a more and more sure knowledge. Nowadays it is tended to believe that determinism is unacceptable either theoretical or practically. Nevertheless it does not mean that the notion of fate has to be legitimazed in all levels.