Descartes employs what is known as an ontological argument to prove the existence of God. Saint Anselm who lived during the 11th century first formulated this type of argument. Since then it has proved popular with many philosophers including Rene` Descartes. Even though ontological arguments have lost popularity with modern philosophers there has been some recent attempts to revive them. Descartes formulation is regarded as being one of the best because it is straight forward and relatively easy to follow. It is also useful when trying to understand Descartes to keep in mind that he talks about two types of existence. There is the normal everyday existence we experience and a special type of existence which he calls, necessary existence. Necessary existence is something our mind can impose on normal existence.
Descartes argument can be presented quite simply as:
(1) Clear and distinct ideas equates necessary existence.
(2) Gods perfection equates clear and distinct ideas.
(3) Therefore, God’s perfection equates necessary existence.
What does Descartes mean when he talks about clear and distinct ideas? Clear and distinct suggest there is an overwhelming amount of evidence that cannot be denied nor contradicted. Let us think about the two most essential properties of a triangle. Firstly, to be a triangle it must have three sides. Secondly, all the angles of a triangle must add up to 180 degs. These two essential properties of a triangle must always be found together if we want to claim that triangles exist. One without the other is of no value when it comes to triangles. For Descartes this is an example of a clear and distinct idea. It is also an example of necessary existence.
In exactly the same way God has two essential properties. Firstly, God’s attribute as a perfect being. Secondly, God’s existence. These two essential properties must always be found together to ensure his necessary existence. Descartes argues that we can no more imagine God not existing then we can imagine a mountain without a valley.
In this analogy Descartes is trying to draw out the distinction between ordinary existence and necessary existence. The idea of a mountain implies a valley. It may be possible to argue that one can imagine a mountain without a valley but such structures do not exist in real life. In the real world mountains and valleys are found together. So mountains imply existence of valleys but unlike the imperfect existence we find in the mountainous world, God’s existence is both perfect and necessary. For Descartes, necessary existence as opposed to ordinary existence is the key.
Descartes is pointing out the difference between the existence of God and the existence of a mountain. Finite things, says Descartes, have possible or contingent existence. For example, a finite thing such as a mountain relies on volcanic forces and weathering to bring it in and out of existence. Necessary existence on the other hand is contained in...