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Background
Background
In the fifth meditation Descartes, having established that God is not trying to deceive us, and having established why we make mistakes, now tries to work out what we can actually know with certainty about stuff ‘out there’ in the world.
Clear and distinct ideas
Clear and distinct ideas
Descartes argues that there are certain mathematical facts about things that we can be certain of simply by thinking about them. For example, we can know for certain facts like:
Every triangle that we come across will have three sides.
Every stick has a length
Nothing can be red all over and green all over at the same time
Every event is temporally related to every other event
Every river has banks
I exist
These are logical and a priori truths (we know them to be true without needing to check their truth via observation, for example). Descartes’ describes such ideas as clear and distinct by the natural light.
‘I find in myself innumerable ideas of things which, though they may not exist outside me, can't be said to be nothing. While I have some control over my thoughts of these things, I do not make the things up: they have their own real and immutable natures. Suppose, for example, that I have a mental image of a triangle. While it may be that no figure of this sort does exist or ever has existed outside my thought, the figure has a fixed nature (essence or form), immutable and eternal, which hasn't been produced by me and isn't dependent on my mind.’
–Meditation VDescartes Ontological Argument
Descartes Ontological Argument
Descartes returns to the question of the existence of God, applying this notion of clear and distinct ideas.
He gives the following Ontological argument - that is an argument where the existence of God is deduced entirely from the concept of God itself:
If God is perfect, then God must have all perfections.
God is perfect (by definition)
∴ God must have all perfections.
Existence is a perfection.
∴ God exists.
In short, God must exist, in the same way a triangle has three sides.
Discussion
Descartes' argument relies on the idea that 'existence' is a kind of description (a predicate). But Kant thought that Descartes was wrong to assume this. If I say that something exists am I actually describing it at all? Kant thought that existence was something that was presupposed by a description, it wasn't a description itself. If, for example, I describe a cup as being blue, I am already assuming that the cup is real. If it's not real, then it's not blue or any other colour.
Tasks
Tasks
Explain Descartes’ idea of clear and distinct ideas.
Explain Descartes’ ontological argument.
Explain one objection to Descartes' ontological argument
Evaluate Descartes' ontological argument.
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