It seems to be generally accepted that metaphysics is posterior to epistemology. After Descartes and Kant nearly everyone seems to take it for granted, even scholastics. For instance, the two books in the previous post, Degrees of Knowledge and Insight, both attempt, each in its own way, to construct a Thomistic-type metaphysics on the foundation of an analysis of the intellect and intellectual processes.
On the other hand, I'm very tempted to argue that the assumption that ever since the formation of the "critical problem" any future metaphysics must be constructed over an epistemological substratum is false, both according to 1) the order of being and 2) the order of knowing.
1). A. Metaphysics is first philosophy. But if it's posterior to epistemology then it's second philosophy. Ergo, etc.
B. Metaphysics is conceived by Aristotle as a science. But according to Aristotle science is certain knowledge logically derived from self-evident necessary first principles. But no singular contingent truth is necessary. Therefore no singular contingent truth is a principle of metaphysics. But the "critical problem" - how can I trust my senses, how do I know I'm not a brain in a vat, therefore how do I know my concepts conform to reality, etc. - is concerned with our knowledge of contingent truths. Therefore a resolution of the "critical problem" is not a necessary precursor to metaphysics.
C. Metaphysics is a science of the necessary, not of the contingent. There is no science strictly speaking of the contingently true. Therefore metaphysics is concerned with a) what is necessarily actual, and b) what is necessarily possible, but not with what is contingently actual. But however the "critical problem" is resolved, it is resolved to a contingently actual truth. For instance, if my senses are generally reliable and I usually perceive the world as it is, taking into account the ordinary risk of error, the fact that this world exists and that I know it is still contingently true. But if I am a brain in a vat and my perception is an illusion, this is also contingently true. Therefore the science of the necessarily actual and possible does not depend on the solution of the problem either way.
D. An accurate metaphysics can persist even if all of my judgments about contingent facts are false. For instance, if I were a brain in a vat, my conception of substance and accidents would remain unaffected. I would be in error about particular substances, but not about the underlying theory. A brain in a vat remains a substance, and its color an accident.
2. A. The possibility of attaining knowledge is not dependent on a proof that the knowledge is possible. A child does not learn semiotics before learning his letters. Phenomenology does not come prior to perception. If I can't prove I'm not a brain in a vat, that doesn't mean that I don't really know who the President is. So, to generalize, a proof that knowledge about reality is possible is not necessary in order to have knowledge about reality.
B. Furthermore, it is licit to argue from actuality to possibility. So: I do know who the President is. Therefore some knowledge about reality is possible. How? That's another question. The fact that I can't show how doesn't prove that it isn't so. A radical doubt which refuses to admit that I know who the President is or whether I have two hands is not asking for epistemology, but something else. It also redefines "knowledge", since it is obviously and trivially (pre-philosophically) apparent that I have knowledge of this kind. If Cartesian radical doubt insists that it is not knowledge in the most perfect sense of "science," then I readily grant this.
C. Even brain-in-a-vat type questions presume a metaphysics. If I am a brain in a vat, then there are bodies with certain properties, and a distinction between material and formal causes, and essentially ordered causal chains, and so forth. A radical skepticism which eschews all metaphysics whatsoever, which makes no claims at all about reality, can be nothing but simple negation. But no science can be founded on a negation. Ergo, etc.
I could go on about why I think the whole notion of Cartesian doubt (as opposed to something like Husserlian epoche) is a serious mistake, but that would take me away from the present topic. As for the thesis, I'd be very happy to read any refutations.
