[488] This means, further, that the critical element, which partly comes from the colleagues and the public discussion about research, also comes from the immediate encounter with the students. And I wouldn't believe that I would know anything about anything without this critical reaction, this wall which must be pierced each time when you get here to the desk, [pierced] in terms of giving convictions, and very often you don't succeed, and then what is said comes back from the wall which you were not able to pierce through. Now that's the

great importance of the combination of teaching and research. In the research^a, the decisive principle is truth. But truth has several levels. There are three levels---and I had a case just last Tuesday, in a group of scholars, colleagues of the different Faculties, mostly of the natural sciences, to discuss the different levels of truth with them. In the introduction for this discussion, I distinguished the truth in the realm of the subject-object experience, analyzing the objects as a subject, and handling them in terms of technical dealing with them. This is the one realm, which one could call, following Max Scheler^b in this, "controlling knowledge," knowledge of control. Then the second, following Plato^c in this respect, one could speak of participation in realities which cannot be known in terms of analysis and control but in terms of participation and eros, as Plato^d called it, namely the other personality, the realms of the good and the beautiful, the intuition of those qualities of being which are not objects of analysis, calculation and management.

Then the third level, existential truth, namely the truth in which we commit ourselves