Rationalism was basically a dead end for philosophy, but an enlightening one. The mere existence of rationalism, a philosophical method in which it was thought that philosophical truths could be revealed by logical deduction from self-evident principles, motivated philosophers to challenge the ability of reason to uncover the truth by itself. And they produced compelling arguments, which I won’t repeat here, to the effect that reason by itself was insufficient, and that truth could only be discovered with the aid of experience. But the best argument against rationalism was rationalism itself. If rationalism was possible we would expect it to be a lot like math: rationalists would produce axioms which they could all agree upon, and from those axioms they would deduce all the philosophical truths. Rationalism then could reasonably be expected to be basically unified and lacking the internal arguments that have always been the hallmark of philosophy. But this is not how things went. Rationalist went in all different directions; rationalist philosophical systems were as varied as philosophy always had been, and there was no indication that they would ever be unified.
Empiricism on the other hand was very successful … in science. In science an empirical method succeeded beyond anyone’s wildest dreams. The empirical method of science led to theories that are unimaginably accurate in describing the world, and which never could have been reached by unaided reason, nor deduced from a priori principles. In philosophy empiricism was successful as well, not as a method for philosophy, but rather as part of epistemology. As an epistemological doctrine it states that all knowledge must stem at least in part form experience. And of course this bothered some philosophers, who realized that philosophy itself didn’t really have a basis in experience, and thus might be disqualified from being called knowledge. To remedy this they attempted to derive complicated systems in which the claims of philosophy were derived from experiences. But none of these systems was completely successful, and eventually the project was dropped.
The problem with all this is that it leaves philosophy as a whole open to radical skepticism, perhaps justified radical skepticism. As I pointed out yesterday a rational argument in favor of a position cannot serve as evidence that that position is true, unless the argument proceeds from evidence. But philosophical arguments don’t have a foundation, ultimately, on evidence; that project was unsuccessful. Thus at best arguments connect the truth of a several different positions (showing that they are all true or all false). But this doesn’t help us at all in determining their truth. And it raises a number of other problems as well (discussed yesterday). And if arguments in philosophy don’t rest on evidence then they must rest on non-empirical premises. But that means that all philosophy that proceeds by argument is ultimately a kind of rationalism. And rationalism doesn’t work.
Another way to look at this problem is by considering how we could possibly discover which philosophical positions we were in error about. And surely we are in error at least some of the time. But each position we hold has arguments in its favor, possibly connecting them to other positions. And nowhere is there an opening to test the truth of our philosophical positions. Sure, we could entertain the possibility that some of the fundamental premises we have been basing our philosophical positions on are wrong, by considering arguments for and against them. But ultimately those arguments rest on premises as well, and we have no way of determining the truth of those premises, and so on. At best all we can do is determine whether our positions cohere with each other, but that is no guarantee of their truth.
The lesson we have forgotten then (or perhaps never properly took to heart) is that reason alone is insufficient to catch the truth. We have thus unknowingly embraced the rationalist method, and it has left philosophy in general with the problems that faced rationalism. How do we know that our simplest principles are true? What do we do when faced with two completely internally consistent theories? And, most importantly, how can we improve our own philosophy?
Unfortunately I raise these questions with no answers to provide for them. I don’t think that we can convert the most basic premises that our philosophical arguments rest on to testable empirical claims. What we need perhaps is an objective way to falsify philosophical theories. Science is so successful because the claims of scientific theories can be tested, potentially revealing the theory as false, and the way in which a theory fails reveals some information about what the theory has failed to capture. If we had such a way to falsify philosophical theories I think we would be in good shape. Now it is true we can falsify some philosophical theories already, by showing that they suffer from internal contradictions, but this is a test for coherence and not truth. But unfortunately a general and objective way to test and possibly falsify philosophical theories is about as hard to create as it sounds, and so far substantial progress in that direction has eluded me.