/lit/ - Literature

I have been arguing with my friend about process philosophy lately. He is very sympathetic to it because he wants a return of authentic speculative metaphysics (not "speculative turn" bullshit, simply real metaphysics). I am extremely sympathetic to this as well, and I am very influenced by Naturphilosophie and Platonism, but we still argue about two basic points:
1) what epistemological ground Whitehead is standing on when he makes very strong metaphysical claims about the real world; specifically, how he overcomes the standard problems that a sceptic would pose to him
2) even assuming he has decent epistemological grounds for his claims, what exactly these claims are; and related to this, how they've been interpreted by his successors.

I am very familiar with pragmatist epistemology and "asymptotic" idealist theories of truth, so I had no problems with the prefatory chapter on method. But I still don't see how it avoids the standard critiques of "asymptotic adequacy" as a criterion of truth, namely that they lead to a bad infinity. Infinitesimally more "adequate" knowledge, especially if knowledge is defined somehow through prediction and experiment in a Jamesian way, still doesn't answer the question of how this can ever be CERTAIN knowledge, let alone complete knowledge. Even if you say there is no complete or certain knowledge, because the nature of nature itself is incompleteness, which I understand is a Whiteheadian thing, you are begging the question, because you've just said in the form of logical certainty and apodictic necessity that nature has no certain and apodictic essence. Even if nature "in itself" is uncertain and open-ended, you still have to justify YOUR certain knowledge OF this proposition.

For a while I thought he hadn't read Kant, but he mentions Kant and seems to know him well. Yet I still don't see how he gets over the essential problem, merely formalized by Kant, of how synthetic a priori judgments, that is metaphysical judgements of necessary character about reality as it is in itself, can ever be made. I just mentioned the problem of finality and certainty in judgment, but the same problem arises in an even simpler form when Whitehead refers to an (at least relatively) stable "God" of some kind as the guarantor of certain things in the system of reality. This is a classic scholastic and idealist move, making God the "uber-observer" of reality, to avoid the problem of reality's self-subsistence in the absence of a mind observing it. But this is a synthetic a priori judgment, i.e., rationalistic. How one can know that nature/God IS a unity, inductively and empirically, if such unity is required for the system to hang together in the first place?