1. Descartes’ ontological argument
Michael Lacewing
© Michael Lacewing

2. Descartes on clear and distinct ideas
Clear and distinct ideas can be known to be true
Clear: Present, accessible to the attentive mind
Distinct: every part is clear, sharply separated from other ideas
The interior angles of a triangle:
The necessity of the proposition compels assent
© Michael Lacewing

3. Descartes’ claim
‘The idea of God (that is, of a supremely perfect being) is certainly one that I find within me…; and I understand from this idea that it belongs to God’s nature that he always exists.’
A rational intuition of a clear and distinct idea?
As with the triangle, the concepts involved force me (logically) to accept the claim
You can think that God doesn’t exist. But this is to think that a perfect being lacks a perfection
And I can’t change the concept of God any more than the concept of a triangle. I discover it.
© Michael Lacewing

4. As an argument I have the idea of God.
The idea of God is the idea of a supremely perfect being.
A supremely perfect being does not lack any perfection.
Existence is a perfection.
Therefore, God exists.
© Michael Lacewing

5. Objection
There is a difference between thinking God exists and God actually existing.
Reply: but you can infer one from the other (as with the interior angles of triangles)
‘from the fact that I can’t think of God except as existing it follows that God and existence are inseparable, which is to say that God really exists’.
© Michael Lacewing

6. Hume’s objection
Nothing that is distinctly conceivable implies a contradiction.
Whatever we conceive as existent, we can also conceive as non-existent.
Therefore, there is no being whose non-existence implies a contradiction.
© Michael Lacewing

7. Hume’s objection
If ‘God does not exist’ is a contradiction, then ‘God exists’ is a relation of ideas
But claims about what exists are matters of fact.
If ‘God does not exist’ is a contradiction, then ‘God exists’ must be analytic
But claims about what exists are synthetic.
© Michael Lacewing

8. Descartes’ response
Descartes could argue that ‘God exists’ is analytic or that it is synthetic, but known a priori
But he doesn’t have these concepts.
Descartes actually says: all divine perfections entail each other
If God is omnipotent, then God must not depend on anything else
Therefore, God must not depend on anything else to exist
Therefore, God must have necessary existence.
© Michael Lacewing

9. Pressing the objection
(from Gaunilo) Descartes’ argument only works if God exists, because only if God exists, is God omnipotent, etc.
The interdependence of perfections shows only that the concept of existence is part of the concept of God
If God doesn’t exist, then God isn’t omnipotent (or anything else), so God’s omnipotence doesn’t entail his existence.
© Michael Lacewing