Theory of Knowledge aims at being a scientific investigation of the very fact which all other sciences take for granted without examination, viz., knowing or knowledge-getting itself. To say this is to attribute to it, from the very start, the character of being the fundamental philosophical discipline. For, it is only this discipline which can tell us what value and significance belong to the insight gained by the other sciences. In this respect it is the foundation for all scientific endeavour. But, it is clear that the Theory of Knowledge can fulfil its task only if it works without any presuppositions of its own, so far as that is possible in view of the nature of human knowledge. This is probably conceded on all sides. And yet, a more detailed examination of the better-known epistemological systems reveals that, at the very starting-point of the inquiry, there is made a whole series of assumptions which detract considerably from the plausibility of the rest of the argument. In particular, it is noticeable how frequently certain hidden assumptions are made in the very formulation of the fundamental problems of epistemology. But, if a science begins by misstating its problems, we must despair from the start of finding the right solution. The history of the sciences teaches us that countless errors, from which whole epochs have suffered, are to be traced wholly and solely to the fact that certain problems were wrongly formulated. For illustrations there is no need to go back to Aristotle or to the Ars Magna Lulliana. There are plenty of examples in more recent times. The numerous questions concerning the purposes of the rudimentary organs of certain organisms could be correctly formulated only after the discovery of the fundamental law of biogenesis had created the necessary conditions. As long as Biology was under the influence of teleological concepts, it was impossible to put these problems in a form permitting a satisfactory answer. What fantastic ideas, for example, were current concerning the purpose of the so-called pineal gland, so long as it was fashionable to frame biological questions in terms of "purpose." An answer was not achieved until the solution of the problem was sought by the method of Comparative Anatomy, and scientists asked whether this organ might not be merely a residual survival in man from a lower evolutionary level. Or, to mention yet another example, consider the modifications in certain physical problems after the discovery of the laws of the mechanical equivalents of heat and of the conservation of energy! In short, the success of scientific investigations depends essentially upon the investigator's ability to formulate his problems correctly. Even though the Theory of Knowledge, as the presupposition of all other sciences, occupies a position very different from theirs, we may yet expect that for it, too, successful progress in its investigations will become possible only when the fundamental