Descartes casts everything into doubt in the first meditation, including God Himself. He then comes to this disproval of this theory therefore concluding that God exists. This is brought about through the causal argument. Desartes begins this argument with the causal principle. This principle states that there must be at least as much reality in the effcient and total cause as in the effect of the cause. Therefore a cause is essential for an effect, meaning that a cause must have as much reality as an effect if not more. Descartes then applies this principle to ideas.
He establishes 2 realities; formal reality and objective reality. Formal reality refers to that what makes an object, what the object is made of. Formal realities can be any of the hierarchy of being- infinite substance, finite substance and mode. For instance the formal reality of a bag is finite, thus a bag is a finite substance. Objective reality refers to ideas only. It is therefore the formal reality of the thing representing the idea. Lets take “ the idea of a bag”. All ideas have the formal reality of a mode therefore its formal reality is that of a mode.
On the other hand, the objective reality of “the idea of a bag” is a finite substance. This is because a bag in itself is a finite substance and because it is an idea, its objective reality is finite. Hence it maybe understood that only ideas of things can have objective realities; a bag (for example) in itself can only have a formal reality while the idea of a bag (for example) can have both formal reality and objective. Descartes henceforth distinguishes between formal and objective realities as previously stated. This then leads Descartes to put the causal principle and ideas together, establishing causal principle ideas.
Descartes asks if the cause of the idea of something can be a mode. As stated above, the cause of an effect must have more reality that the effect itself. An idea of something has the formal reality of a mode yet the objective reality of the “something”. Thus, if the example of the bag is used, the idea of a bag has the objective reality of a finite substance. So taking the causal principle into perspective, the cause of this idea must be either a finite substance or an infinite substance because the cause must have the same or a higher reality.
If we then ask the question “can the cause of the idea of a bag be a mode? the answer would be no. The reason being that the idea of a bag has an objective reality of a finite substance so the cause must indeed be finite or infinite. The essence of the Causal Argument is then discussed after all this was established. Descartes brings up the idea of God and questions it. He had put even God into doubt in Meditation 1 and this argument is resurfaced in Meditation 3. “The idea of God” , as every idea, has the formal reality of a mode yet its objective reality is unique. It has the objective reality of an infinite substance.
An infinite substance in itself refers to God. Due to these facts, Descartes himself, or any human for that matter, cannot be the cause of such an idea because they are finite substances which has less reality than an infinite substance. Hence, Descartes concludes that only God Himself can be the cause of the idea of God because an infinite substance is the only possible cause to an idea of the objective reality of an infinite substance. This is Descartes proof of the existence of God. Through further reference to Descartes’ first meditation, this eliminates any doubts of God.
Descartes states that whatever is clearly and distinctly perceived is true and God is good. Hence, the evil demon theory in the first meditation is eliminated. If God is good then we cannot be being deceived by an evil demon because God would not let us be deceived like that. Through “whatever is clearly and distinctly perceived is true”, we understand that we are not dreaming, we are existing and living. Descartes builds the rest of his meditations on this. Before everything was cast into doubt, now the truths are being revealed through these foundations.