Descartes on the External World [2]

2025-1 Descartes

 

1. Descartes argues that bodies do not have features like color, taste, sound, scent. What is his argument? What is the external world like, for Descartes, if bodies in fact exist? How does Descartes' view represent a dramatic turn in the history of science?

He argues that the most basic features of body are size, shape, and extension. That is to say – color, taste, sound, smell, temperature, and other sensory qualities are not among the basic features of body. We could strip a body of such features, and it would still be a body. (For example, transparent bodies have no color, but they are still ã David Cunning bodies.) But then he notes that if bodies have no color at the most basic level, color would not be able to magically emerge at a macroscopic level. So bodies do not literally have color (or taste, sound, smell, etc.). Here we have Descartes giving a very early argument for a linchpin of the contemporary scientific worldview.

Descartes reflects the view in numerous passages, indicating that color and such are really just subjective sensations in human minds. He grants that it’s fine to say that color is out in the world, so long as we are careful to note that all that we are saying is that there are (color-less) bodies that occasion or prompt such sensations in our minds. In contemporary science we do that; we say that color is just a wavelength, for example, but we are not thereby suggesting that color (as we experience it) is out there in bodies.

But the Sixth Meditation argument for the existence of material things is then really odd. The argument is in effect that we have sensory perceptions – ideas of bodies that have size, shape, extension, color, sound, etc. – and that those ideas must have a cause that transmits the ideas into our mind. We have an extremely strong inclination to believe that external bodies are the cause of those ideas – Descartes is supposing that we just feel that inclination – and because God exists and is not a deceiver, external bodies must exist.

But Descartes does not think that external bodies transmit ideas of size, shape, extension, color, sound, etc., into our mind. Bodies do not have color, sound, etc. In addition, our ideas of size, shape, and extension are not transmitted from bodies either. Descartes had argued in the Second Meditation that those ideas far outstrip what we experience through the senses, for example with respect to the number of sizes and shapes that a body can take. In some passages Descartes says that our idea of extension is innate – and so it is not produced by external bodies – but at most it is prompted or occasioned by external bodies. He says the same about our ideas of sensory qualities like color. A radical consequence follows from the conclusion that sensory qualities like color and sound are not literally in objects. Descartes holds that it is primarily by color that we are able to differentiate the objects that surround us – for example the brown bark of the trees is separated from the green grass along the river, which is separated from the gray cement of the EPB parking lot, all of which are distinguished from the transparent air. Or even if a person saw slightly different colors, or if they saw all the colors as just different shades of grey, discriminations between the various objects would still be possible.

But color – the central feature by which we discriminate between objects – is not actually out there. Or perhaps a blind person discriminates object by their feeling of the texture of an object. But that feeling is subjective also. (Descartes does not emphasize that case, but he has the resources to draw the same conclusion.) He concludes that our sensory perceptions of bodies do not inform us of the actual details of those objects, but instead they just provide us with guidance on how to navigate our surroundings. That is in part to say that we do not really recover from the dream argument of the First Meditation. The world is not as we perceive it with our senses.

 

2. What is Descartes' argument for the existence of the external world? Discuss one potential objection to the arguement. If we assume for the moment that the argument actually works, what does Descartes think we actually know about the external world? Can we be certain about the existence of trees, rivers, and other particular objects?

In the Sixth Meditation Descartes offers a proof of the existence of the external world. He says that when we have a sensory perception of a material object, there is an idea of the object that appears in our mind – for example a sensory idea of a red ball or a blue river – and there is also a cause of the appearance of the idea. Appealing to the language of the Third Meditation, he says that the cause of the idea must have formal reality and that that formal reality produces the idea. Then he asks what that formal reality might be. One option is material bodies themselves; another is our own minds; another is God; another is a creature other than a mind or body. He argues that we are not the cause of our own sensory ideas. We cannot just will ourselves to have a sensory perception of pizza, for example, so we do not have the power to produce sense perceptions in ourselves. Furthermore, the mind is highly conscious and reflective, and we would notice if there was some faculty in our mind that produces our perceptions, but we do not notice any such faculty at all. [Here Descartes is leaning heavily on his Second Meditation view of mind as conscious and reflective.] Instead, what we notice is that any time we have a sense perception, we have an extremely strong inclination to believe that it was caused by material things. God would be a deceiver if we had that inclination but material bodies did not exist; so material bodies do exist.

Even if we grant (for the sake of argument) that God exists and is not a deceiver, one of the problems for the Sixth Meditation proof is that Descartes is on record as holding that sensory qualities like color and taste and sound do not exist in material objects. If so, then he cannot say that those qualities are transmitted from the outside world into our ideas. He is also on record as holding that our idea of extended size and shape is not produced by external bodies. He says in the Second Meditation that our idea of extended size and shape far outstrips the finite inputs that we get from our sense perceptions, and he says elsewhere that our idea of extended size and shape is innate. He says that same about our ideas of qualities like color, taste, sound, etc. – as we would expect if he holds that such qualities do not exist outside of our minds and are not transmitted into our minds from bodies.

So the Sixth Meditation proof of the existence of material things is in big trouble. Descartes offers an amended proof in Principles of Philosophy. He gets rid of any notion that external bodies produce ideas of color or sound (or extended size and shape) in our minds, and instead he speaks of ideas of color and sound and extended size and shape as being occasioned in our minds. The ideas are already in our mind, and external bodies just trigger or activate them. The argument is that when we have a sense perception, and we inquire into the cause of that perception, an extremely vivid (and clear and distinct) idea of body pops into our mind. It’s a kind of signpost that body is the occasion of our sense perceptions. God would be a deceiver if that signpost was so vividly presented to us, but bodies did not exist. And so bodies do exist. But not with sensory qualities like color, taste, and sound. Bodies only have the features that are reflected in our clear and distinct idea of body – extension, size, shape, mass, and also any features that are able to arise or emerge from these, for example motion.

we cannot be certain of the details of particular sensible objects. If we have an idea of such an object, we can be sure that the idea does not match anything – for example, there are no red bodies. Nor can we draw any firm conclusions about the size, shape, or motion of the bodies that surround us. The only way that we are able to demarcate the size, shape or motion of a particular object is by detecting its sensible features – like color and sound. But those features are not actually in objects. Descartes concludes that we do not know the configurations of bodies as they are in themselves.

Still, our sensory perceptions do seem to be tracking something. We feel pain when damage is done to our body, and we feel fear when we hear the roar of a lion or bear. Descartes concludes that we do not achieve certainty about the existence of lions or bears, etc., but instead our sensory systems are set up to provide us with information that is helpful for navigating our surrounding environment. Descartes says that insofar as each of us is a union of a mind and a body, we have extremely obscure perceptions of the bodies that surround us, but that those perceptions are very useful to help us to remain a mind-body union. If we just had clear and distinct ideas all day, we would not survive very long.