and regrets it. Both usually believed that there were definitely unanswerable questions, and both found them in the metaphysical region. The difference was that the empiricist was convinced that all problems lying in that region were insoluble, while the rationalist believed he could solve the most important ones of them by means of his reason.
This issue between rationalism and empiricism went on continuously through the centuries, and the chief reason why rationalism was very often deemed to be victorious lay in the fact of the existence of what is called logical and mathematical truths. All the best thinkers from Plato’s time on recognized that these truths certainly did not rest on any experience, and yet nobody could deny that they not only were really true, but even the most firmly established truths of all, and without doubt applicable to reality. But if this were so, then there were certain questions (those of logical and mathematical nature) which could be answered without consulting experience, and our criterion which we thought could distinguish soluble problems from those that are in principle and definitely insoluble, would break down.
There is no time to explain here in full how much depends for philosophy on the decision of this issue, but it has always been felt by the deepest thinkers, and therefore they concentrated their whole energy on the discussion of the so-called logical and mathematical truths. They felt that almost everything in philosophy was decided, if they could understand the nature of those particular truths. Kant based his whole system on such an investigation, and he really believed that by it he succeeded in overcoming the dispute between empiricism and rationalism.
In reality he has not succeeded. His solution of the problem was just as unsatisfactory as that given by the empiristic school, for instance by its most famous leader in the nineteenth century, John Stuart Mill. He endeavored to prove that reason alone could not solve any problems at all and that the only test for the truth of any proposition lay in experience; he attempted to show that logical and mathematical propositions (such as 2 + 2 = 4) had no other reason for being true than that they were always found to be so in experience. But a critical examination of his argument reveals the most serious mistakes in it, and we must conclude that he failed utterly in his attempt to show the empirical nature of logical or mathematical propositions.
