Meditation V: Overall Summary

This meditation deals with two things: the nature or essence of the physical world, and another argument for the existence of God.

Firstly, Descartes concludes that in his mind exist ideas (corresponding to mathematical and geometrical principles) that suggest that physical reality exists. He then goes on to consider possible sources for these ideas.

Next, he provides the second of his arguments for the existence of God, called the ontological argument. This deals with the idea that the existence of God is necessary, because for Him not to exist would be a contradiction in terms. He then outlines three possible objections to this argument and provides his own answers to them.

Finally, Descartes puts forward the proposition that all absolute knowledge relies on knowledge of God, because He is not a deceiver, and so we can trust our clear and distinct perceptions.

The Arguments:

Material Essence

In examining the contents of his own mind, Descartes finds that the ideas therein embody certain mathematical and geometrical truths (as he concluded in the example of the wax). In other words, they represent principles of shape, motion, number, etc., which suggest how - if the real world does exist - the objects within it might have their existence, interact with one another, etc. So, theoretically, these ideas tell him that the existence of a physical world is logically possible and coherent. Do these ideas, then, prove that such a world exists?

Firstly, he rejects that he himself has made up these ideas, because they have properties he cannot have foreseen (e.g. the mathematical properties that a triangle possesses, such as it's internal angles adding up to 180 degrees, or other mathematical truths which he cannot have known in advance). Secondly, he dismisses the idea that he has learnt these ideas through experience, because there are some concepts which he has never experienced (e.g. a 10,000-sided shape).

Having reached these conclusions, he therefore decides that the material world may in fact exist (or at least, that it is feasible that it does). Actual proof for it, however, will have to wait until the next meditation.

The Ontological Argument

First put forward by St. Anselm (1033-1109), the ontological argument argues that the idea of such a being as God necessarily entails that being's existence. In more detail, the argument goes like this:

• I have an idea of God.
• The idea of God implies that such a being exists eternally.
• For this being not to exist, therefore, would entail a contradiction (a God who did not exist eternally would not be God).
• Therefore, since I obviously have such an idea, this being must exist.

Descartes then imagines three objections to this, and provides his own response to them.

1st Objection:

We can conceive of God as not existing, therefore existence is not an essential quality of God. Therefore, God may not exist.

Descartes's Response:

Perfection is also one of God's qualities, and for Him not to posses the quality of existence would represent an imperfection. Therefore He must exist.

2nd Objection:

We cannot conceive of mountains without valleys, yet this does not mean that there must be any mountains (or valleys). After all, I can imagine a winged horse, that is just my mind putting together two ideas - perhaps that is all we are doing with God and existence?

Descartes's Response:

Existence is essential to God, so the idea of God is not like that of a winged horse (which I can imagine with or without wings). (It is, Descartes would argue, more like the idea of a triangle and the property of having internal angles that add up to 180 degrees - that is what we mean by a triangle; therefore, a being with necessary existence is part of what we mean by 'God').

3rd Objection:

Even if the idea of God entails His existence, there is no necessity to think of the concept of such a being in the first place. What gives us the right to think that such a concept is coherent?

Descartes's Response:

Whenever we think of God, or a perfect being, the ontological argument must be true. So, he argues, imagine that we did not have such a concept as that of a triangle, still, whenever we thought of a shape having 3 sides in a certain arrangement, the concept would be forced upon us.

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