Franz Brentano_The True and the Evident.pdf

1
ON THE GENERAL VALIDITY OF TRUTH
AND THE BASIC MISTAKES IN A
SO-CALLED “PHENOMENOLOGY”
I
Brentano to Husserl
Florence, 9 January, 1905
Dear Friend,
I thank you for your cordial letter and good wishes which I warmly return. I have read
with great interest what you say about your endeavours, over the long years that have
separated us, and about your present point of view.
If I understand correctly, you distinguish a twofold logic. One is an art, 1 the other a
theoretical discipline. The latter is supposed to comprise all pure mathematics (geometry
apparently being a discipline which is applied only to space). What is its subject-matter? 2
Apparently objects of reason and their combinations. It is supposed to be a part of
philosophy and not to be based upon our knowledge of psychology. And this latter seems
to you to be the point of greatest importance, for otherwise the validity of logic could be
restricted to beings who happen to have the same make-up as we do. 3 This theoretical logic
is concerned, not with evidence for us, but with an evidence of truths in themselves, so to
speak. You praise Bolzano as your teacher and guide.
I must admit that I have several misgivings and I will not hesitate to mention them.
For even if you too should have second thoughts, you need not be discouraged. 4 For it
does seem clear, generally speaking, that all or most of the questions which you take up in
your so-called theoretical logic will find their proper place in other classifications of the
sciences. 5
I think you may be justified in holding that the task of pure mathematics falls within the
sphere of logic. But what seems unclear to me is whether this logic is anything other than
the art of logic.
We do speak of the “art of calculating”, after all. And in mathematics do we not learn
to perform certain logical operations, such as adding, subtracting, multiplying, dividing,
extracting square roots, and so on?
Was not the discovery of the differential calculus, in particular, the discovery of a
mathematical procedure, with the result that Leibniz’s symbolism, so superior to that of
Newton, proved to be a great step forward? Even the invention of calculating machines
could be mentioned.
To be sure, not only do we learn how to add, but we also learn certain laws, certain
equations stating what adds up to what, as “2+5=7”; not only do we learn to multiply,