Earlier in the week, I discussed Voltaire's engagement with and endorsement of the following Posidonian argument:
(I) A necessary condition of the possibility of (an (intended)) successful scientific representation or concrete model of (a region of) nature is that (a region of) nature is orderly;
(II) (A region of) Nature’s hidden order could not be the product of chance [as suggested by Epicureanism] or necessity [as suggested by Spinozism], but only by God;
(III) [It’s possible that] Science produces successful representations and successful concrete models of (a region of) nature.
(IV) ∴ There is a God (of order).
I noted in passing that Voltaire ridicules Spinoza. But I did not explain why Voltaire would do so, although it's pretty clear from a moment's reflection. In the early modern period this argument is taken to establish the existence of final causes because the God of order just is taken to be the god of providence. Voltaire, in fact, is quite explicit about this because he subsumes final causes under (and restricts them to) general, universal laws. And the ordering god is a law-giving god. So far so good.
But Voltaire (and with him many earlier folks -- Boyle, Derham, Clarke, etc. -- committed to natural religion and this argument) ignores the fact that premise (II) has a problem. For present purposes, the problem is not that the independent arguments against chance or necessity fail to convince. Rather the problem is that (II) is not exhaustive. There is, in fact, an overlooked possibility that may be the source of Nature's (apparent) hidden order: the human mind or imagination. This possibility is, in fact, raised by Spinoza in the Appendix to Ethics 1, in the context of his attack on final causes: “as if order were anything in Nature more than a relation to our imagination.” (The translation is due to Curley.) This is, in fact, hard to miss point because Spinoza echoes it several times in that very Appendix. For example, "And because those who do not understand the nature of things, but only imagine them, affirm nothing concerning things, and take the imagination for the intellect, they firmly believe, in their ignorance of things and of their own nature, that there is an order in things."
It's pretty clear, say, that in the traditional (old Hume/skeptical interpretation of) Hume, Hume thinks it is extremely plausible that natural order is a projection, or, if one is more Kantian about it, constituted by the mind. So, then inspired by Spinoza-Hume (II) would have to be rewritten as follows:
(II*) (A region of) Nature’s hidden order could not be the product of chance [as suggested by Epicureanism] or necessity [as suggested by Spinozism], but either by God or human projection;
It is implausible, perhaps, that the human mind is the source of Nature's actual order, but the idea really becomes that the human mind is the possible source of apparent natural order, and so we really cannot infer God from (a) successful scientific representation(s) of nature.
But the defender of the argument has a response. She may ask, look what explains the apparent long history of scientific success if we presuppose that the mind's spreading order onto nature? How come the mind is so good at projecting order onto nature over time. What secures the robustness of the pattern such that our scientific practices and mappings seem so efficacious (especially if we rule out miracles) in terms of predictions and representations?
What this response brings out is that lurking behind the Posidonian argument is a commitment to PSR (and the denial of brute facts). The argument really relies on the commitment that there are no unexplained facts and that success at representing nature is also one of the facts to be explained. This itself cannot be the consequence of chance/necessity (already ruled out) or a miracle (against the background rules and also favoring those who wish to see god behind natural order). So, to introduce the human mind as the source of apparent natural order only pushes the question back one level. In fact, one may argue that in one sense it makes it utterly mysterious what we take ourselves to be doing when we produce representations or measures of nature, and do so over many centuries.
And taking the human mind seriously as the source of natural order opens the door to a rather extensive forms of skepticism about the possibility of knowing anything about the true nature behind the appearances we constitute. Now, I think this helps explain why a certain strain of skepticism about nature's hidden order is, in fact, common ground among (say) Spinoza, Hume, and Kant. And, why restricting the scope and import of the PSR becomes such an urgent matter. But about that some other time, more.