The monograph offers an in-depth, source-oriented presentation and analysis of the complex discussions that took place between ca. 1230 and 1350 on the differentiation and expansion of the structural concept of scientific knowledge and certainty in lifeworld-contingent areas of investigation. It makes transparent a development in the course of which a graduated, multidimensional conception of knowledge and certainty emerges. In the process, the masters gain pioneering insights into the philosophy of science. Starting from the key data provided by Aristotle, the scholastic scholars' productive, far-reaching further thinking leads to a deeper understanding of the nature and reliability of scientifically acquired knowledge. These intellectual endeavours were significantly challenged by the increasing knowledge of the spectrum of the transmitted Aristotelian and Arabic sciences. They also received significant impulses from epistemological reflection in theology.