Justificationism in Continental Rationalism leads to a situation of salvation and damnation. The epistemologist must save some commonsensical ideas, such as other minds, an external world, the reliability of science, and cast out or exorcise supposed illegitimate foundations. She sorts out the desirable from the undesirable statements, yet to begin this sorting this requires a proper sorter.
Out of all the possible foundations for knowledge, all but one foundation will fail to correctly sort out all desirable positions. If a foundation does not succeed, it will fail to deliver the promised goods. It is one thing to question whether the system is coherent; it is another to question whether it accomplishes its task. For instance, if a proposed foundation asserts the existence of the external world, this is not a satisfactory foundation, for it does not tell us anything of importance about the external world. We are not searching for a meta-criterion, but as a criterion of preferable foundations. I want a foundation that doesn’t let too much in, yet keeps all the riffraff out.
Descartes’ theory of knowledge rests (in part) in his clear and distinct ideas; however, that does not guarantee truth, for in order for his ‘clearness’ and ‘distinctness’ to work its magic, Descartes cannot be mistaken about the status of his ideas: their truth is still up to debate. Thus, on a much deeper level, Descartes’ optimistic epistemology rests on the theory of veracitas dei: the truthfulness and goodness of God must make truth manifest.
Descartes requires a perfect being that would not deceive him, yet he is still left with the insolvable problem of the dualism of an immaterial mind and a material body. If, for the sake of argument, we assume these problems to be solved, Rationalism must still explain error, for it assumes perfection. Why do we make mistakes? Why are we often wrong about our clear and distinct ideas? Here we arrive at Kant’s observation that clear and distinct ideas can lead to two conflicting theories (Kant’s “antinomies”). It would be impossible on the basis of clear and distinct ideas alone to decide rationally between such theories. Thus, even if Rationalism provides a foundation for knowledge, it is the foundation of very little. I will not discuss such arguments that consider the error of experience, or delusions, or dreams. I will only ask the question of whether or not Rationalism successfully solves the problem of justifying knowledge.
Descartes’ arguments for the existence of a truthful and good God do not hold water. That much is assumed, since his arguments been covered by everyone. For instance, historically, different Rationalists regarded different things as being self-evident, with no way to rationally resolve the disputes. If once the naked truth stands before us, we have the power to see it, one immediately wonders why so many have discovered conflicting self-evident truths. Hence the systems of Descartes, Spinoza and Leibniz produced very different results.
Without God-the-touchstone, Rationalism suffers under a ‘fork’: (1) Rationalism is a foundation for a very small number of trivial statements relating to a world outside of the mind; (2) Rationalism lets too much in that qualify as justified, that is, any idea that appears to any individual to be clear and distinct (“antinomies”).
Why this discussion of Rationalism? It’s a label for the concept of the a priori. That’s all the discussion has been about: is the foundation for knowledge to be found in the workings of the mind?
Once these two foundationalist theories of knowledge were shot down, then new pessimistic foundationalist theories were developed: Kuhn’s and Wittgenstein’s ideas of the social, of ‘language games’ and ‘games of life’, of ‘paradigms’ and ‘lexicons’. Once they’ve abandoned the possibility of a priori or a posteriori certainty, they give up on the regulatory idea of truth that extends beyond the social realm, and suffer immensely for it. They’re two of the more respectable philosophers to take the social turn, but there are plenty of others that continue their foundationalist program (at least in its authoritarian scope) without the hefty intellectual consequences of empiricism or rationalism. Social foundationalism, in order to work, gives up on truth as a goal, saying that truth is determined by economic class, or race, or gender, or social class, etc.