Cassie asked:

What exactly are Descartes’ cosmological and ontological arguments?

Answer by Craig Skinner

Traditional arguments for God’s existence include:

1. Cosmological argument (the world can’t be self-caused or uncaused, it needs a First Cause (God).

2. Ontological Argument (God’s existence provable from the very definition of God).

3. Design Argument (the universe shows evidence of design, a designer must exist).

4. Moral argument (God needed to underpin right and wrong).

All are flawed. Neither Descartes nor anybody else has proved that God exists. Belief in God is a matter of faith and revelation, but alleged revelations to date are wide open to doubt.

You refer to Descartes’ versions of the Cosmological (or Causality) argument (Meditation 3) and Ontological argument (Meditation 5).

The existence of God is crucial to Descartes because in the sustained argument of 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.

Descartes does not set out his arguments in formal deductive terms (he antedates predicate logic and was no fan of syllogistic logic). He uses scholastic terminology. At times he seems to think that God’s existence is readily evident to any diligent, attentive meditator, and 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. For all these reasons, the meditator has to do some work to penetrate the arguments.

For each argument, I shall set out a fair construction and briefly consider objections.

Cosmological (Causality) Argument:

P1: I have the idea of a most perfect (infinite, eternal,omnipotent, benevolent) being (God).

P2: A cause must be at least as great (real) as its effect.

Conclusion: this idea of God can’t come from (imperfect) me. Its cause must be God (or, impossibly, greater). God exists.

P1 is clear.

P2 is less easy to grasp. Discussion is couched in technical, scholastic terms. Two types of reality (being) are distinguished regarding ideas. The existence of an idea (its formal reality) is distinguished from the content of the idea (its objective reality). “Objective” refers to the object contained in the idea, rather like the modern use of “subjective” – it refers to the tree (say) in the mind not the tree in the garden. The notion of degrees of reality is then introduced. Ideas all have the same degree of formal reality, all being states of mind, but they differ in degrees of objective reality – lowest in a “mode” (modification of a substance e.g. shape), intermediate in a finite substance, highest in an infinite substance.

So P2 expresses the Causal Principle that the degree of formal reality of the cause must be at least as great as the objective reality of the effect, leading to the conclusion that an idea whose content (objective reality) is infinite (such as my idea of God) can’t have its cause in a finite being (with less than infinite formal reality) such as me, only in God, so that God exists.


P1: I can claim not to have this idea.

P2: Whether expressed in scholastic or modern terms, P2 is simply an assertion. No evidence is given for it. To assume a finite mind needs an infinite mind to cause it begs the question as to God’s existence. As far as I can see simple things plus simple rules can lead to complex things e.g. laws of nature plus simple initial conditions has produced atoms, compounds, galaxies, life and minds, so that the Causal Principle is false.

The argument is valid but unsound.

Ontological Argument

Originally due to Anselm, declared invalid by Aquinas, the argument lapsed, and Descartes’ use of it surprised his contemporaries.

His 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.


P1: again, I simply deny that I have this idea.

P2: this is fine if we mean that the conceived entity can be thought of AS IF it existed necessarily. It doesn’t mean that any such entity actually exists, or indeed could possibly exist.

P3: in support, Descartes makes a famous geometrical comparison, 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.

To which Gassendi makes 2 penetrating objections (5th set of Objections).

1. 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.

2. Existence is placed among God’s, but not among the triangle’s perfection. Also existence is not a perfection, it is that without which no perfection (or other quality) can be present. Gassendi anticipates Kant’s view that existence is not a predicate.

Also, the traditional objection to the ontological argument applies, that we can prove the existence of anything e.g. I have a clear and distinct idea of a necessarily existing perfect pizza, holiday, partner etc.

The argument is invalid.

All we can really conclude from Ontological arguments 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.

Finally, both arguments face the following objections:

1. Vicious circularity: 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 by the existence of a non-deceiving God.

2. No criteria for clear and distinct perception. No guide to recognizing slightly unclear or somewhat indistinct ideas which we can’t rely on. In any case, it’s quite common for people to have clear and distinct ideas which turn out to be wrong.

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 required by philosophers and for persuasion of infidels. He was no doubt disappointed by criticism, rather than acclamation, of his arguments by theologians (and others) which he published as Objections with his Replies along with the Meditations, and which are as worthy of study as the main text.