Now, the rules of logic and of pure mathematics represent all the truths which have their origin in “pure reason,” and of which it is so proud. But we see, that their “truth” and general applicability, which cannot be denied, are of a very particular, insignificant kind: they are merely formal, they do not convey any knowledge, they do not deal with any facts, but only with the symbols by means of which facts are expressed.
In this way the only apparent support of rationalism breaks down. The real nature of logical and mathematical “propositions” has been elucidated: the new empiricism does not deny their absolute truth and their purely rational character, but it maintains that they are “empty,” they do not contain any “knowledge” in the same sense as do empirical propositions; pure reason is unable to produce any real knowledge, its only business is the arrangement of the symbols which are used for the expression of knowledge.
After so-called “rational knowledge” is accounted for, empiricism now has the right and the power to claim the whole field of knowledge. We know nothing except by experience, and experience is the only criterion of the truth or falsity of any real proposition. You will remember that verifiability by experience was also the criterion of those questions that can in principle be answered. By holding these two results together we conclude that there are no really insoluble problems at all. All proper questions and all proper propositions (which can always be considered as answers to certain questions) are related to experience in the same way: they arise from it, and they can, in principle, be answered and tested by it. But what about those apparently insoluble problems which we seemed to discover among the questions of philosophy? “How do physical processes in the brain produce mental processes?” “Are animals or plants conscious beings or not?” What becomes of these problems?
Fortunately the same analytical methods which helped us to understand logic and mathematics (and at which I could not even hint in this lecture) permit us to answer the question and do away with all difficulties which it seems to hide. Again I can only indicate the result without being able to prove my point on this occasion. Reduced to the shortest formula the result is simply this: the so-called insoluble problems are in principle insoluble, because they are no problems at all. It is true they have the io
