Sunday, May 9, 2010

Logical vs Metaphysical Necessity

One of the problems I have with analytical philosophy is the tendency to fail to distinguish between logical and metaphysical necessity. Or, more precisely, it is to invert the priority of being and logic.

The Maverick Philosopher wrote a post the necessity of God that exemplifies this tendency.

The MP refers to "philosophers in the tradition of Anselm and Aquinas" who define God as a necessary being, and he takes them both to mean the same thing - logical necessity. But St. Thomas rejected Anselm's Ontological Argument precisely because he understood the necessity of God to be a metaphysical necessity, not a logical necessity.

Logical necessity refers to the relationships of the terms of propositions to each other. Thus a "logically possible world" is one that involves no propositional self-contradiction. No logically possible world can contain married bachelors, because bachelors are by definition not married. But there is no self-contradiction in supposing that a body can be at two different places at the same time; for example, that you could be in Boston and Binghamton simultaneously. That it is not possible for you to be in both Boston and Binghamton at the same time is a consequence of your incarnate nature; it is the nature of bodies as such that they occupy one and only one place. It is a metaphysical necessity. Thus "John is in Binghamton and in Boston" is logically possible, but metaphysically impossible.

When Thomists discuss the necessity of God, they mean that God is metaphysically necessary, not logically necessary. There is no logical contradiction involved in denying the existence of God. But it is to assert a metaphysical impossibility. The Thomistic arguments for God are all different ways of revealing this metaphysical necessity.

6 comments:

PSEUDONOMA said...

Great post.

Any historian of that comparatively brief history of philosophy specified by the name "analytic" cannot, if he is an honest one, fail to appreciate the foundational importance not only of David Hume but also, and perhaps even more so, of Immanuel Kant. Kant's bequest is certainly not to be ignored even in this very matter of the distinction drawn between logical and metaphysical necessity. Indeed, that it is Kant who mediates between the analytic tradition's interpretation of necessity as an inherently logical relation and the pre-modern tradition's insistence that the logical relation of necessity is made possible by metaphysical conditions (the principle of non-contradiction is, after all, a first principle of forst philosophy according to Book Gamma of the Metaphysics)can be observed in the fact that A.J. Ayer, in order to fully erect the logical empiricism that his "Language, Truth, and Logic" so desperately wants to establish, sees fit to directly attack and subsequently dispatch with Kant's synthetic a priori. In other words, the notion of metaphysical necessity that you correctly observe to be conspicuously absent from analytic philosophy in general was deliberately rejected only after the notion of necessity was divided into analytic and synthetic necessity --a move which clearly already approached necessity from the vantage point of the judgment, and hence of logic. Analytic philosophy simply dismissed synthetic necessity, but Kant had already shifted the foundation according to which necessity was to be understood (a fact even more glaringly obvious in Kant's peculiar formulations of the postulates of empirical thought, i.e. the modalities). So, all of this leads to me to ask you, how do you distinguish between the concept of necessity operative as a crtiterion (along with strict universality) for all synthetic a priori judgments and the concept of metaphysical necessity that guides Thomas's ways? And as an afterthought I would add: do you think the same concept of necessity (as is operative in the "ways") is in play in De Ente et Essentia's "proof"?

David T. said...

thanks for the kind words.... your questions will take some thought...

David T. said...

Your second question is too much for me... I'd like to hear what you have to say about it.

As to the first, my impression of Kant has always been that he essentially took classical metaphysics and transplanted it from reality (i.e. being) into the realm of thought. This was the strongest impression I had reading the Critique of Pure Reason; how surprisingly Aristotelian it was, except that its object was thought instead of being. So where Aristotle would say that substance is necessary to the reality of change (in true being), Kant would say that we must posit substance as a cognitive synthesis necessary to rational experience; in other words, we can't avoid thinking about reality in terms of substance, but this is a fact more about our cognitive apparatus than being itself.

So I would say the metaphysical necessity of Thomas is a necessity in being itself, where for Kant, since being itself bears no necessity (or, at any rate, any we can know about), the necessity in the synthetic apriori is a necessity of the human cognitive apparatus and nothing more. For Thomas, necessity in our thought is a reflection of necessity in being; for Kant, it's at best a necessity of cognition.

RSL said...

David T,

Thanks for your post. Your response to Pseudonoma is right on the money. However, I have some concerns about your description of Anselm's argument -- at least insofar as one restricts oneself to the Book II formulation of the argument in the Proslogion.

You write, "St. Thomas' rejected Anselm's Ontological Argument precisely because he understood the necessity of God to be a metaphysical necessity, not a logical necessity." You add "When Thomists discuss the necessity of God, they mean that God is metaphysically necessary, not logically necessary. There is no logical contradiction involved in denying the existence of God. But it is to assert a metaphysical impossibility."

What you affirm here of Aquinas' argument, I think, holds equally for the Book II version of the ontological argument in Anselm. In that book, Anselm does not define God as a "necessary being" or as an "existent being" -- rather, he comes to understand that the concept of God is just the conept of being "that than which none greater can be conceived." Moreover, there is no evidence that Aquinas ever rejects Anselm's argument -- first, because Aquinas never names Anselm as the object of his critique, and second, because Anselm never claims that God's existence is self-evident.

If Aquinas' arguments for God's existence are valid and sound, then it would be contradictory to affirm thier premises and then deny the conclusions. And this is no more than what Anselm is saying when he presents his reductio. In fact, if all of the five ways are sound arguments, then any of them could just as easily be reformulated as reductios like Anselm's argument.

Best Regards,

Dr. Lee

David T. said...

Dr. Lee,

Thanks for stopping by and reading my blog, and I appreciate your corrections. I'm going to reread/rethink Anselm in light of your remarks...

David Brightly said...

996That it is not possible for you to be in both Boston and Binghamton at the same time is a consequence of your incarnate nature

And your small size compared to the separation of those cities. But consequence is a logical term.