Descartes and the ontological proof of God’s existence

Chun asked:

Descartes’ argument for God’s existence in the 5th Meditation.

Lay out the structure of Descartes argument for Gods existence in Meditation 5. What is the crucial premise in the argument, and what evidence does Descartes provide for it? How might we object to the argument.

Answer by Craig Skinner

You refer to Descartes’ version of the Ontological Argument.

The existence of God is crucial to Descartes because in the sustained argument which is the Meditations, God is the bridge from the hyperbolic doubt of the Cogito back to knowledge of the empirical world and the abstract world of logic and mathematics.

On the other hand he seems to think that God’s existence is readily evident to any diligent meditator, and that arguments are just heuristic devices to help the slower meditator to the almost self-evident truth that God’s existence is known by clear and distinct perception.

He doesn’t set out his arguments in formal deductive terms (he antedates predicate logic and was no fan of syllogistic logic), and he uses unfamiliar scholastic terminology.

For all these reasons, the meditator has to do some work to penetrate the arguments.

An Ontological Argument tries to prove God’s existence from the very definition of ‘God’. Originally advanced By Anselm (his definition of God being the ‘greatest conceivable being’), this was declared invalid by Aquinas, and the argument lapsed. Descartes’ use of it surprised his contemporaries.

A fair construction of Descartes’ version is as follows:

P1: I have a clear and distinct idea of a most perfect being.

P2: This idea includes necessary existence.

P3: God’s necessary existence is part of God’s essence.

Conclusion: God exists.

You speak of ‘the’ crucial premise and evidence for it. I think all 3 premises are crucial.

What evidence does he provide for the premises?

P1: he gives no criteria for clear and distinct perception, either here or elsewhere in Meditations when he mentions it. No guide to recognizing slightly unclear or somewhat indistinct ideas which might be unreliable.

P2: no evidence given, but none needed, or indeed possible. We can accept that necessary existence is a feature of the being he has in mind.

P3: here he relies on Aristotelian and Scholastic thinking about essences: all things which come into existence have an essence (roughly a nature), but existence is not part of this essence — these things are contingently not necessarily existing, dependent on an essentially necessary being (God) to bring them into and sustain them in existence. Also in support, Descartes suggests a geometrical analogy, saying existence can no more be separated from the essence of God than the fact that its three angles make two right angles can be separated from the essence of a triangle.

How might we object to the argument?

We can object to all three premises.

P1: I can deny that I have this idea. In any case, it’s quite common for people to have clear and distinct ideas which turn out to be wrong.

Also,the argument is circular (question-begging): the conclusion that a (non-deceiving) God exists is based on a clear and distinct idea, but the truth of clear and distinct ideas is guaranteed only by the existence of a non-deceiving God.

P2: this is fine if we mean that the conceived being can be thought of AS IF it existed necessarily. It doesn’t mean that any such hypothesized being actually exists, or indeed could possibly exist. To imagine otherwise is to confuse ‘God (necessarily) exists’ (correct, by definition, semantic claim) with the existential claim ‘(Necessarily) God exists’, a simple logical fallacy (changing the scope of the modal operator from de re to de dicto), as Aquinas pointed out. This allows us to ‘prove’ the existence of anything e.g. I have a clear and distinct idea of a necessarily existing perfect pizza, holiday, partner, etc.

P3: Two penetrating objections to the geometrical analogy were made by Gassendi (5th set of Objections to The Meditations).

(a) The comparison is unfair. Like is not compared with like. Essence is (correctly) compared with essence, but then existence is not compared with existence. Rather existence (of God) is compared with property (of a triangle). A fair comparison would not show God necessarily exists any more than that a triangle necessarily exists.

(b) Existence is placed among God’s, but not among the triangle’s perfections. Also existence is not a perfection, it is that without which no perfection (or other attribute) can occur. Here, Gassendi anticipates Kant’s view that existence is not a predicate.

The argument is invalid.

All we can really conclude is that if God exists his existence is necessary, if he doesn’t his existence is impossible, but we don’t know whether God exists or not.

In the Meditations’ dedication (to a Faculty of Theology, he hoped to get the Churchmen on his side) Descartes says that although faith suffices for the faithful, proof is needed by philosophers and for persuasion of infidels. Doubtless he was disappointed by criticism, rather than acclamation, of his arguments by theologians (and others) which he published as Objections and Replies along with the Meditations, and which are as worthy of study as the main text.

You might think the Ontological Argument died the death, but it just wont lie down. We find Plantinga in the 20th century championing the modal version:

P1: If God exists his existence is necessary

P2: If God doesn’t exist his existence is impossible

P3: Hence God’s existence is either necessary or impossible

P4: God’s existence is possible (not impossible)

P5: Hence God’s existence is necessary

Conclusion: God exists

I wont rehash the flaws, but notice the argument just as easily ‘proves’ God’s nonexistence, thus:

P1: If God is nonexistent his nonexistence is necessary

P2: If God isn’t nonexistent his nonexistence is impossible

P3: Hence God’s nonexistence is either necessary or impossible

P4: God’s nonexistence is possible (not impossible)

P5: Hence God’s nonexistence is necessary

Conclusion: God is nonexistent.


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