Setting the stage

Descartes begins with what he thinks he has established in the previous meditations (Descartes [1641] 2019, 47R).

1. He exists

2. Whatever he perceives “clearly and distinctly” is true. The expression “by the light of nature” is equivalent to “clearly and distinctly.”

He says that he used to think he clearly perceived external objects, like chairs and trees. Now he realizes that he only clearly perceives ideas, that is, thoughts that represent chairs and trees.¹ He also wonders whether a supernatural being like God could deceive him about simple mathematics, like 2 + 3 = 5.

He distinguishes between three things in his mind (Descartes [1641] 2019, 47R).

1. Ideas: these are images that could represent real things or could be imaginary. If I am on a sheep farm, looking at a sheep, my mental image of the sheep will represent a real sheep. If I am in bed counting sheep, my mental image of sheep will not represent real sheep. I am just imagining sheep in order to fall asleep.

2. Volitions: we would use words like “intentions” or “the will” for these. Volitions are thoughts that lead to action, such as “I want to pick up the pencil.”

3. Judgments: these are the things that can be mistaken. The thought “that’s a real tree” is a judgment that there is a real tree that is causing my mental image of a tree.

Then we get two questions that he is going to answer (Descartes [1641] 2019, 48L).

1. Is there a God?

2. Could God be a deceiver?

Two arguments for God’s existence

There are two arguments for the existence of God in the Third Meditation: the argument from the idea of God and the argument from preservation.

In the course of spelling these arguments out, Descartes introduces some distinctions that you are probably not familiar with, such as the distinction between “formal reality” and “objective reality” and the distinction between “substance,” “mode,” and “accident.” Let’s start with those terms.

The formal reality of an idea is that it exists. Things that do not exist do not have formal reality. Easy! You would think that the objective reality of an idea concerns whether the idea accurately represents an object in the world, but you would be wrong. Not easy! An idea’s objective reality only consists in what it represents. So when I am thinking about my cat, the formal reality of my thought is that there is a thought. The objective reality of my thought is that it is about a cat. Whether the cat that I am thinking about exists outside my mind is a separate issue from the idea’s objective reality.

Substances are not ideas but things that exist on their own, without depending on anything else. To be more precise, a substance is “a thing that is suitable for existing in itself” (Descartes [1641] 2019, 51L). For example, Descartes says, a stone is a substance. Modes and accidents are things that do not exist independently; accidents depend on substances and modes depend on accidents. The stone is a material substance, meaning it is extended or has spatial dimensions. Extension is its attribute and its size and shape are modes of that attribute. In order to be a material object, the stone has to be extended so that is where the attribute comes into play.² That extension can have different modes: it can be six inches or six miles long and have a round or a rectangular shape, and so on.

The idea is that substances are more real than attributes and attributes are more real than modes. Correspondingly, the ideas of substances will have more formal reality to them than the ideas of attributes, and the ideas of attributes will have more formal reality to them than the ideas of modes. As far as the objective reality of ideas is concerned, there is another three level analysis of reality. Infinite substances have more reality than finite substances and finite substances have more reality than modes. In turn, ideas of infinite substances have more objective reality than ideas of finite substances do and ideas of finite substances have more objective reality than ideas of modes do.

I have to be honest with you here. I am not sure I understand what he is trying to say and I am not at all clear about how much the argument depends on these distinctions. But that is what he is saying.

With all that in hand, let’s look at the argument from the idea of God.

1. An effect (such as an idea) cannot have more reality than its cause (such as a tree or God). (Descartes [1641] 2019, 49R–50L)

2. The cause of my ideas of things other than God could be in myself. These include ideas of corporeal and inanimate things, angels, animals, and other human beings. I have at least as much reality as these things do so I could be the cause of my ideas of them. (Descartes [1641] 2019, 50R–51L)

3. I have an idea of God. Its objective reality is of a substance that is infinite, independent, supremely intelligent, supremely powerful, and it created everything that exists (Descartes [1641] 2019, 51R)

4. This idea could not have been caused by anything in a finite thinker such as myself or, indeed, by anything other than God. (Descartes [1641] 2019, 51R–52)

5. Therefore, God must be the cause of my idea and so God must exist.

After making that argument, Descartes adds the argument from preservation (Descartes [1641] 2019, 52R–53R). This one maintains that Descartes’s existence through time depends on God. This paragraph seems to me to express the central idea.

I must now ask myself whether I possess some power by which I can bring it about that I myself, who now exist, will also exist a little later on. For since I am nothing but a thinking thing — or at least since I am now dealing simply and precisely with that part of me which is a thinking thing — if such a power were in me, then I would certainly be aware of it. But I observe that there is no such power; and from this very fact I know most clearly that I depend upon some being other than myself. (Descartes [1641] 2019, 53)

1. I know that I am a thinking thing.

2. I am sustained through time; I continue to exist from one moment to the next.

3. All I know about a thinking thing is that it can think. I do not know that it is capable of sustaining itself through time.

4. Therefore, my existence through time must depend on something else.

5. That something else must be God because God is the only thing whose existence does not depend on anything else.

6. Therefore, God exists.

God is not a deceiver

There were two points Descartes was supposed to make: God exists and God is not a deceiver. He slips in the second one at the very end.

He asserted that his idea of God is an idea of an infinite and perfect being. He argued that he could not have this idea unless it were caused by a being that is infinite and perfect.

Now he asserts that only an imperfect being would be a deceiver: “it is manifest by the light of nature that all fraud and deception depend on some defect” (Descartes [1641] 2019, 54L). If that point is granted, then God cannot be a deceiver because God is perfect.

Here I want to talk about an argument made by Pierre Bayle in the entry to his Historical and Critical Dictionary on Zeno of Elea. It runs as follows.

It is no proof at all that there are bodies to say that our senses assure us of this with the utmost evidence. They deceive us with regard to all of the corporeal qualities, the magnitude, size, and motion of bodies not excepted; and when we believe them about these latter qualities, we are also convinced that there exist outside our souls a great many colors, tastes, and other entities, that we call hardness, fluidity, cold, heat, and the like. However it is not true that anything like these exists outside our minds. Why then should we trust our senses with regard to extension? It can very easily be reduced to appearance, just like colors. (Bayle [1697] 1991, 373)