Interest in epistemological questions is not limited to philosophy today. Numerous empirical sciences have, in the normal course of their research, been forced to proceed from the immediate object of their research to questions involving cognition. Quantum physics is perhaps the best-known example, but it is no exception. In linguistics the question is raised today of what problems arise from the fact that research into language has to make use of language. Cognitive instruments have to be aquired via the object investigated by means of these very instruments and not, for example, through reflection of consciousness upon itself.1 Brain research has shown that the brain is not able to maintain any contact with the outer world on the level of its own operations, but — from the perspective of information — operates closed in upon itself. This is obviously also true for the brains of those engaged in brain research. How does one come, then, from one brain to another? Or to take a further example: the sociology of knowledge had demonstrated at least the influence of social factors on all knowledge, if not their role as sole determinants. This is also true, then, for this statement itself since no justification for an exception can be found, in the sense, say, of Mannheim’s »free-floating intelligence«. What conclusion is to be drawn from this? It was thought that one would have to found all knowledge on »convention«2 or that knowledge was the result of a kind of »negotiation«.3 But these attempts only wound up designating an ancient problem — that of the unity of knowledge and reality — by means of a new concept. Not without reason have these attempts been criticized for epistemological naiveté4, since one either learns nothing about the relationship to reality or the connection is only made over theoretically unacceptable »both/and« concessions. There is little more to be gained by calling such »constructivism«, as has recently been done, »radical«5 since what is identified here as »constructivism« hardly at first seems unfamiliar. It might be that the theory of knowledge — at least in some of its traditional variants — will be confirmed rather than caught unaware. Science is apparently reacting here to its own power of resolution. This can already be found in Plato who reduces everyday experience to mere opinion and raises the question of what reality lies behind it. As a result, these philosophic reflections were termed, at first, »idealism«. As we come to modern times the emergence of modern science led more and more to the conclusion that this »underlying« reality was knowledge itself. This altered the meaning of the concept of the subject, while it is only in our century that the name »idealism« has been replaced by »constructivism«. There was a shift in emphasis in the conflict between realism and idealism, but it is not easy to discover in this a new theory. There is an external world, which results from the fact that cognition, as a self-operated operation, can be carried out at all, but we have no direct contact with it. Without knowing, cognition could not reach the external world. In other words, knowing is only a self-referential process. Knowledge can only know itself, although it can — as if out of the corner of its eye — determine that this is only possible if there is more than only cognition. Cognition deals with an external world that remains unknown and has to, as a result, come to see that it cannot see what it cannot see.