In his book Meditation, Descartes says, “I must inquire whether there is a God as soon as the occasion presents itself; and if I find that there is a God, I must also inquire whether He may be a deceiver; for without a knowledge of these two truths I do not see that I can ever be certain of anything.”
To lay the foundation for this inquiry into the existence of God, Descartes considers his thoughts, which to this point are the only thing he has to consider and prove his existence as a thinking thing. Thoughts can be divided into two general categories. The first is that of ideas. Ideas are “images of things” and are a mode of thought within himself. He gives the examples of man, chimera, heaven, an angel, and God. Ideas are the basic type of thought to which additional forms of thought (the second category) may be added. This other category is subdivided into volitions and judgments. Examples of this type of thought are willing, fearing, approving and denying. Thoughts in the second category must always have as their subject an idea from the first category. Descartes finds that only the subcategory of judgment is liable to have error, the most common of which is to judge that the ideas he holds “are similar or conformable to the things which are outside me.” Ideas, say of a man, are true by definition as modes of thought, but if he judges that the idea of a man inside him has a formal reality outside of him he may have erred. For, he has noted, his sense perceptions are not always accurate and furthermore, the idea of a man will necessarily be an abstraction. Though if he considers the idea of a specific man, Bob Jones, the idea will not be an abstraction, but still subject to inaccuracies.
Descartes proceeds to consider the reasons which cause him to believe that his ideas resemble objects outside of him. A natural impulse or spontaneous inclination seems to be a lesson from nature which confirms the resemblance, but upon reflection Descartes rejects this thought because such impulses in the past have “led [him] to the part that was worse.” A second reason is that these ideas do not depend on himself or his will. This is also rejected as there may be some unknown part of him which is producing this illusion of being outside his will simply because he does not recognize it within himself; or the idea may not be a true resemblance of an object outside himself. The final possibility is ideas which are images are very different from one another. Those ideas which represent substances have a higher degree of perfection or objective reality in them. The idea of a Supreme God has more objective reality than ideas of finite substances for Descartes and modes or accidents have even less objective reality than substances. Given Descartes’ conception of an infinite, immutable, omniscient, omnipotent Creator of all things outside Himself, thereby possessing the unfathomable extension of being, steadfastness, knowledge, power and creation this God does seem to be perfection.
Descartes then gives us an axiom as it is made manifest by the natural light. “There must at least be as much reality in the efficient and total cause as in its effect. For, pray, whence can the effect drive its reality if not from its cause? And in what way can this cause communicate this reality to it, unless it possessed it in itself?” And he further says, “But in order that an idea should contain some one certain objective reality rather than another, it must without doubt derive it from some cause in which there is at least as much formal reality as the idea contains of objective reality.” Any idea must, therefore, be placed in a person by something that possesses at least as much formal reality as the objective reality perceived in the representation.
As there are three levels of objective reality (infinite, finite, mode) there must also be three levels of formal reality. Therefore, God, if he exists, has a high level of formal reality corresponding to a high level of objective reality; man has a moderate amount of formal reality and modes of thought have little formal reality. A chimera has no formal reality or existence, despite having objective reality in the mind.
Descartes’ argument from the above axiom is if he can find a representation within himself for which he is clearly not the formal or eminent cause that he is not alone in the world because something greater than he must have been the cause of this idea. This is the idea of God. Since the idea of God has high objective reality it must have high formal reality if God is a substance. Like a chimera, it is possible to have an idea of something which does not have formal reality, so the physical reality of God is still doubtful.
Descartes goes on to bolster this argument with the example that he would not be able to identify his lack of perfection unless he had within himself an idea of the perfect, the God. He would likewise be unable to doubt or desire. To doubt would indicate that a possibility exists to not be something. To desire would be to recognize the possibility for something greater to be obtained. The idea of God or perfection is a necessary contrast to Descartes’ idea of himself (the only two possible options in his limited sphere) in order to doubt or desire.
The possible argument that Descartes is attributing to God that which is merely possessed by himself already but didn’t recognize he dismisses by saying that he would not be lacking knowledge of this fact if he was omniscient.
The argument that the God Descartes calls God is not the ultimate God is inconsequential because it is still the case that in order to be the cause of the idea of God in a thinking thing there must ultimately be something that possesses the attributes Descartes attributes to God and the immediate conception of God possessed by a finite thinking thing does not negate the necessity of there being such a being.
The idea that the attributes which Descartes believes are possessed by one God are actually the attributes of many gods is set aside simply by the fact that Descartes cannot conceive God to be any different than He clearly and distinctly is.
Descartes argues that God not only created him but conserves him from moment to moment. This is so because existence in the past does not necessitate existence now and the same power which created in the first place must be present to allow continuation of existence.
The question of where this idea of God originated is answered by referring to the three types of ideas, which are innate, adventitious and formed by the self. Innate ideas are those which are from the mind or existing perpetually in the mind. Adventitious ideas are those which are presented to the mind through the senses or from impulses. This idea of God was not formed by the self because Descartes finds that he cannot change his conception of God, which he would be able to do if he had formed it initially. This idea was not presented suddenly to him as adventitious ideas are when they are sensed. This leaves only the possibility of the innate. God has implanted the idea of himself in the mind as part of creation. Descartes finds it likely that this knowledge of God is not only the mark of the Creator on his work (man) but actually is the work of God.
God cannot be a deceiver. To deceive would be a defect and God exists possessing all of the supreme perfections which the idea of God has.
Having now established the basic pattern of being able to find in existence the thing which is represented by a clear and distinct idea, the possibility exists to find many other corporeal substances.
Not only does Descartes exist because he thinks, but Descartes knows God exists because he is able to think about Him clearly and distinctly.