Leibniz and Henry of Ghent on Possibility

January 25, 2008

Judging by his previous post, it looks like my man Keith has been reading some Leibniz.  I must confess, I’ve only just  began reading Leibniz seriously just recently.  I did some reading a while back in an Early Modern Phil. class but I don’t remember much from back then.  One interesting point though about the early modern thinkers is the remarkable continuity they exhibit with their medieval predecessors (despite their strong repudiation of them). 

Consider the the nature of possibility: In the Monadology, Leibniz insists that the ‘essences or possibles’ depend on the ideas in God’s understanding in such a way that if God did not exist, then ‘not only would nothing exist, but also nothing would be possible.’  The eternal truths or abstract realm of possibilia are for Leibniz so dependent on God, that their very possibility emerges from him.   But what does that mean?  Specifically, Leibniz’ claim is that ‘the possibles’ depend on the divine intellect itself.  Here, he tries to repudiate Duns Scotus’ understanding of God and possibility while avoiding the pitfalls of Descartes:

We ought not to say, with some Scotists, that the eternal truths would subsist, even if there were no understanding, not even God’s.  For, in my opinion, it is the divine understanding that makes the eternal truths real, although his will has no part in it.  Whatever is real must be founded in something existent.  It is true that an atheist may be a geometer.  But if there were no God, there would be no object of geometry…The reason for truths lies in the ideas of things which are involved in the divine essence itself.

By making this move, Leibniz is appealing to the doctrine of divine ideas associated with Augustine and Aquinas, which says that God’s knowledge extends as far as He knows His essence to be imitable in this way or that, and that there exists in God an idea of every such imitation that He knows.  So in God, there are ideas of everything that exists, even of things that do not in fact exist, but are simply possible.  Now Leibniz thinks that God’s will has ‘no part’ in determining what is possible.  This is the sole perogative of His intellect.  He has in mind the likes of Descartes who, in his letter to Mersenne appeared to embrace a kind of voluntarism:

As for the eternal truths, I say once more that they are true or possible only because God knows them to be true or possible.  They are not known as true by God in any way which would imply that they are true independently of him…In God willing and knowing are one single thing, in such a way that by the very fact of willing something He knows it, and it is for this reason that such a thing is true.

And in another reply to Mersene, May 27, 1630 he says:

You ask me by what kind of causality God established the eternal truths, I reply: by the same kind of causality as he created all things, that is to say, as their efficient and total cause.  For it is certain that he is no less the author of creatures’ essence than he is of the existence; and this essence is nothing other than the eternal truths.

He goes on to maintain that it is because God has willed it that all the radii of a circle are of equal length or that it is again in virtue of the divine will that all the angles of a triangle are necessarily equal.  But Leibniz in no uncertain terms, rejects this thesis.  Necessary and possible truths have their status not because God has willed that they do.  This would imply that it is within God’s power to will that such truths have a different nature altogether.  Hence, God could have made it that 2 + 2 = 7 or that a necessary conclusion would not come from a valid syllogism with true premises.  So Leibniz rejects Descartes’ view, but he does not want to give the impression that he is with Scotus either.  His via media then is this: Whatever is possible is possible in virtue of God somehow, if only because the divine intellect makes it possible.  Leibniz never really fleshes out this claim, however.

As it turns out, Leibniz proposal is remarkably similar to that of Henry of Ghent (one of Scotus’ favorite interlocutors), and here we find a bit more flesh.  Henry proposes one of the clearest responses to the impasse posed by the statistical model of possibility for God’s freedom to create.  On Aristotelian modality, no genuine possibility could forever remain unactualized.  In fact Aristotle himself had insisted that per impossible, if an object were to have contrary potencies, one of which is always actualized, then the alleged unactualized potency could not in fact be real.  Yet this concept of modality seemed to entail that God could not have the freedom to create things that He would otherwise not have.  But God’s perfect freedom in creation was a central theological doctrine that the medieval thinkers could not contradict.  Henry’s solution was to posit that the possibilities do in fact have some kind of realization in the divine intellect.

            Now Henry argued that in the divine mind there exists a kind of reality consisting of all things that might take place in the actual world.  These objects have a quasi-reality about them albeit somewhat less that the being of actual objects.  They have a “being of essence” and are real enough to be called “conceivable things.”  These objects derive their formal possibility from their relation to the divine intellect itself.  Their being conceived by the the divine mind is what makes them possible.  Opposed to these, are the absolute nothing of fictions, Henry says.  These are simply the things that are impossible like the Chimera or Aristotle’s goat-stag.  These have no being or reality at all for they are not objects of the divine intellect and thus do not derive any formal possibility from this relation.  So the possibility of things is derived from the divine intellect itself, whereas impossibility is derived from the absence of a relation between an ostensible thing and the divine mind.  So for Henry as for Leibniz, an object derives its very possibility from the divine mind such that if God did not exist, not only would it not exist in the actual world, it would not even enjoy its formal status as possible.