  On the occasion of Carl Friedrich von Weizsaecker's 81st birthday, a
colloquium was held on July 3, 1993. One of the topics was "The epistemological
foundation of physics from Kant to von Weizsaecker". I took part in the
discussion. Afterwards I got the impression that I had not succeeded in making
my points clear. Therefore, I wrote an explanatory letter to Prof. von
Weizsaecker. This was the beginning of a correspondence on the questions
intimated by the title above. In addition, a private discussion between Prof.
von Weizsaecker and myself took place. Some readers may be interested in the
answers which Carl Friedrich von Weizsaecker has given to the naive questions
and views of a physicist with only a rudimentary education in philosophy. The
starting point of our discussion was my remark that the conspicuous inability
of philosophers to agree on the deepest elements of human existence including
the basic questions of ethics, which is tantamount to the occurrence of
different schools of philosophy competing with each other, could perhaps be
traced back to the fundamental inability of man to attain self-knowledge.
Physicists, on the other hand, can reach consent, in an equally remarkable way,
on the results of their measurements and on whether or not these results agree
with the ideas of theory. They just have to deal with res extensa. Here the
yardstick does not intend to measure itself, but objects which are external to
it, and this is possible. There remains only the question what consequences can
be drawn from this realization. Is philosophy, in as much as it gives
statements on the totality of human existence, only an expression of the
prevailing social circumstances and views, interesting enough as such, but not
a gateway to truth?
