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Do Physical Things Really Exist? Descartes' Surprising Answer in His Sixth Meditation

Is the world around us real? Do physical things truly exist? This question seems absurd, but it plays a fundamental role in Descartes Meditations on First Philosophy, specifically the Sixth Meditation. His goal? To find a foundation of knowledge that is absolutely certain.

Why question physical reality?

This question is born in the search for indubitable foundations of knowledge. The hyperbolic and methodological doubt of Descartes has put into question the existence of physical things. He imagined the possibility that everything he experiences could be a dream or a deception by an evil demon. However, if physical things do not exist, we need to acknowledge that physics, astronomy, and all other sciences with physical things as their objects are doubtful. 

Descartes’ scepticism has led him to conclude one thing for certain: “I am, I exist” (often known by the slightly different formulation cogito, ergo sum). That’s not enough! Descartes also wants to rebuild all knowledge on this foundation. That includes knowledge from sciences like physics, astronomy, and biology. In order for these sciences to be worth something, Descartes has to prove that physical things exist.

Descartes’ starting point: sensing

Descartes has already established, in earlier meditations, that he exists. Why does he feel the need to meditate further and examine the existence of physical things? What makes him suspect that there are physical things? The answer: sensing!  Even while meditating and doubting everything, Descartes notices a passive faculty for sensing things. For example, we feel heat, see colour, or hear a sound. These sensations just happen to us. We don’t create them consciously. They’re received.

Descartes infers that if we receive these ideas, then there must be something producing them. This is an application of a principle he established in his third meditation: everything has a cause. If everything has a cause, then these sensations also have a cause. This leads to the idea of an active faculty that creates these sensory ideas. The question is: What is this active faculty?

Step 1: The active faculty can’t be inside us.

Descartes first considers whether it is the soul itself that creates these sensory ideas. Could we be imagining or thinking up the sensations of heat or colour ourselves?

This hypothesis is rejected for two reasons:

  1. Sensory ideas are stronger and more vivid than the ones we imagine or think up ourselves. For example, there is a difference between seeing a painting and imagining a painting. A painting that is seen is much more detailed than a painting that is imagined. The same goes for pain. Sensing pain and imagining pain are two very different experiences. 

  2. These ideas occur without our control or consent. We can’t force ourselves to feel pain or to sense a colour when these are not presented to the mind. They just happen. We also cannot stop ourselves from feeling heat or pain when we do not want to; we do not control these sensory ideas.

Descartes concludes that this active faculty must exist outside of him.

Step 2: What is this active faculty? 

Descartes has ruled himself out as the source, but there still must be an active faculty that produces sensory ideas. Therefore, Descartes proposes three hypotheses as to what this faculty might be:

  1. Physical things (bodies). This is what we ordinarily think to be the causes of sensory ideas. For example, by standing close to a fire, I feel heat. This hypothesis implies that physical things exist.

  2. God. Believers and non-believers can agree that in metaphysics, it is possible that God sends us sensible ideas. After all, God is supposed to be all-powerful.

  3. Some other being nobler than physical bodies (like angels or spirits)

Each of these is a candidate for what causes our sensory experiences. By examining them one by one and eliminating those which are impossible, we can infer what this active faculty is.

Step 3: Ruling out God and other beings

According to Descartes, God cannot be the cause of our sensory ideas. This is for a very specific reason. If God gives us the strong impression that these ideas come from physical things when they actually don’t, he would be deceiving us. This strong impression comes from sensing. Physical things are often presented to us at the same time that we receive a sensory idea. I feel heat when I stand close to a fire; therefore, it seems as though the fire causes this heat. I feel pain the same time I see that my foot has stepped on a Lego; therefore, it seems as though the Lego caused my pain. Why does this strong inclination matter?

Descartes has already concluded earlier that God is not a deceiver. If God were deceiving us by sending us sensory ideas himself, then he would be a deceiver. This is impossible. So, God does not send us sensory ideas himself. The same logic applies to the idea that another powerful creature (like an angel) gives us these ideas. If God allowed this, it would still be deception, and God doesn’t deceive.

Since there are no other hypotheses left, Descartes infers that physical things cause our sensory ideas. Therefore, physical things must exist!

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