I. Objective

A. So Far: Descartes knows for certain that he exists and that he is thinking and he knows what he is thinking.

B. Descartes at this point still only has access to things in his own mind.

C. He needs/want to get to knowledge of the world—which is external to or independent of his mind.

D. To bridge the gap between knowledge of his mind and knowledge of the world, Descartes needs to argue for the existence of God.

E. It seems at this point that Descartes must argue for the existence of God solely from what he knows of his own existence and his own mind.

F. Thus Descartes needs an a priori-style argument for the existence of God.

II. The Epistemic Principle

A. Descartes thinks that he can establish the following principle on the basis of what transpired in Meditation Two:

Whatever I clearly and distinctively perceive is true.

B. Argument?

P1: I know that I exist and that I am thinking.

P2: The only thing these propositions have to recommend themselves to me, epistemically speaking, is that I clearly and distinctively perceive them to be true.

C: So whatever I clearly and distinctively perceive must be true.

C. Objection: Some things have seemed to me clear and distinct that turned out to be dubious.

1. A Posteriori Judgments: I can clearly and distinctively perceive that there is a hand in front of my face.

2. A Priori Judgments: I can clearly and distinctively perceive that 1 + 1 = 2.

D. Reply: There is a difference between things seeming to be clear and distinct and their really being clear and distinct.

1. A Posteriori Judgments: I do clearly and distinctively perceive that I am having certain sensations, that things seem a certain way to me. I then confuse this with clearly and distinctively perceiving that some particular object is the cause of these sensations or appearances.

2. A Priori Judgments: Perhaps I do clearly and distinctively perceive these, but I can generate at least metaphysical doubt about them, which thus deteriorates the original clarity and distinctness.

E. It looks like Descartes is committed to using doubt as a test for clarity and distinctness. Or at least that, if one can generate doubt about a proposition, then it is not clear and distinct.

III. The Causal Principle

A. Descartes contends that by the natural light of reason he clearly and distinctively perceives that the following must be true:

The cause of anything must have at least as much reality as the effect.

B. The ‘reality’ of ideas: Ideas represent objects that may be real or not. But the objects represented can be said to have degrees of reality. We then say that ideas have a certain degree of ‘objective’ reality.

C. Kinds (Sources) of Ideas

1. Innate: The idea has always been in mind

2. Adventitious: Idea arises in mind from some external source

3. Fictitious: Idea is merely constructed by the thinker

D. Implication of the Causal Principle

1. Ideas have some form of objective reality

2. All ideas have some cause—internal or external to the mind

3. Ultimately the cause of an idea must have as much formal (actual, true) reality as the idea has objective reality.

IV. Argument for the Existence of God (I)

P1: I have an idea of God as an infinitely perfect being.

P2: If I have an idea of an infinitely perfect being, then some infinitely perfect being must exist.

2a: The cause of any idea must have at least as much formal reality as the idea has objective reality.

2b: Only an infinitely perfect being has as much formal reality as my idea of God has objective reality.

2bi: My finite mind itself could not have been the source of the idea. (My idea of God is not innate)

2bii: I could not have constructed the idea of God by compounding other ideas. (My idea of God is not fictitious)

2biii: Nothing external that was not infinitely perfect has enough formal reality to cause my idea of God.

C1: So the cause of my idea of God must really be infinitely perfect.

C2: So God, an infinitely perfect being, exists.

V. The Cartesian Circle (I)

A. Descartes’ can know that God exists only if he knows that the Causal Principle is true.

B. Descartes can know that the Causal Principle is true only if he can know that he clearly and distinctively perceives that the principle is true.

C. He can know that he clearly and distinctively perceives that the causal principle is true only if he can resist doubting the principle.

D. He can resist doubting the principle only if he can rule out the possibility of an evil genius deceiving him about the principle.

E. He can rule out the possibility of an evil genius deceiving him about the causal principle only if he knows that an all-good, non-deceiving God exists.

VI. The Cartesian Circle (II)

A. Descartes’ argument for the existence of God in Meditation Three relies on the epistemic principle.

B. The epistemic principle is justified only if God exists.