This talk by Michael Della Rocca is based upon a paper forthcoming in The Oxford Handbook of Spinoza. It is an important fragment of his project of arguing for the Principle of Sufficient Reason (PSR). The goal of the talk is to identify where Hume’s resistance to this principle ultimately derives from. Why does Hume reject the PSR? Why does anyone reject the PSR? These are important questions given the premise that the existence of God (i.e. a necessarily existing being) entails the truth of the PSR (in some sense). What Della Rocca wants to argue is that we must choose between a strong endorsement and a strong rejection of the PSR, that is, between something like Spinoza and something like Hume. He locates most philosophical positions (e.g. Kant) between these two extremes, in an impossible no mans land.
Arguments for atheism based upon the rejection of the PSR have two main parts. First, against the Spinozist, there has to be an argument for the existence or reality of contingency, i.e. for an existent being that might not have existed (or vice versa), or a proposition that is both possibly true and possibly false. Many atheists and theists simply take contingency (or the slightly weaker thesis of real distinction I am about to consider) for granted, but I think it is unwise (or at least uninteresting) to assume the falsity of Spinozism (thus construed) in this context. Second, there must be an argument for why Spinoza is right to construe the PSR in the strong way that he does, i.e. as excluding contingency and/or real distinction. Putting these parts together, the argument is that necessary existence and the PSR are incompatible with either of these things, and should therefore be rejected.
My interest in Della Rocca’s argument has to do with the connection between the PSR and acosmism, which can be glossed here as the view that ‘the world’ or ‘appearances’ do not strictly speaking exist – or as James Van Cleve puts it in a different context, the view that modes are mere constructions that should not be quantified over by any ontologically perspicuous language. To be clear, Della Rocca does not straightforwardly accept that Spinoza is an acosmist. But he does read him in a way that evinces sensitivity to the pressure exerted by the PSR in the direction of acosmism. He proposes a novel means of accepting the PSR whilst diverting this pressure: roughly, that modes express degrees of existence. (Thus rather than say that there exists a thing x that is not fully grounded, we say that x is fully grounded to degree of existence n, and otherwise non-existent.)
Della Rocca holds that the Humean assertion of real distinction is incompatible with the PSR. If two things are really distinct it is possible for each to exist without the other. For example, first I am smelling flowers but not seeing a doggy (p & ¬q), and then I am seeing a doggy but not smelling flowers (q and ¬p). Here is the point: if you want to be a Spinozist, Della Rocca tells us, you have to be prepared to deny that anything is really distinct. As such, it cannot be that there is a doggy and flowers and then a doggy without flowers or vice versa. Rather, to the extent that these things exist, they are not really distinct. This turns out to mean that only one thing fully or completely exists (i.e. Substance).
However, if one applies this denial to the appearances themselves, one ends up saying that the flowers and the doggy do not even appear distinct, and it is not clear how to make sense of this without rejecting (p & ¬q) and rejecting (q and ¬p). Put differently, what I am suggesting is that if there are truths about the appearances as such, then there are arguably truths of the form (◊(p & ¬q) & ◊(q and ¬p)), that express real distinction, which ex hypothesi is incompatible with the PSR. So to preserve the PSR we had better deny that there are such truths, or else deny that the PSR applies to all of them. Neither option is particularly satisfying from the Spinozist viewpoint.
Della Rocca’s complaint is that Hume assumes the reality of real distinction without argument. And he is surely right that Hume does not really argue for his fundamental assumptions. That is just a disappointing fact about Hume’s work (and perhaps about all philosophy) that we have to learn to live with. On the other hand, I do not think that the consequences of Spinozism have been fully appreciated – specifically that there may be more to the Hegelian charge of acosmism than is typically thought. The seriousness of Hegel’s charge depends in part on the viability of Della Rocca’s resolution of the problematic (in)compatibility between real distinction and the PSR. It is often thought that we do not have to choose between giving up the PSR and endorsing Spinozism, but can instead have our cake and eat it too. If this were so it would justify being indifferent to Spinozism and its consequences. But if Della Rocca is right then this is mistaken.