Part 6b

Sensory Ideas

by Rene Descartes Icon

Sensory ideas must be produced by some substance other than me. This substance actually has (either in a straightforward way or in a higher form) all the reality that is represented in the ideas that it produces.


  1. this substance is a body, in which case it will straightforwardly contain everything that is represented in the ideas; or
  2. it is God, or some creature more noble than a body, in which case it will contain in a higher form whatever is to be found in the ideas.

I can reject 2, and be confident that God does not transmit sensory ideas to me either directly from himself or through some creature that does not straightforwardly contain what is represented in the ideas.

God has given me no way of recognizing any such ‘higher form’ source for these ideas. On the contrary, He has strongly inclined me to believe that bodies produce them.

So if the ideas were transmitted from a source other than corporeal things, God would be a deceiver. But He is not and that is why bodies exist.

They may not all correspond exactly with my sensory intake of them, for much of what comes in through the senses is obscure and confused. But at least bodies have all the properties that I clearly and distinctly understand, that is, all that fall within the province of pure mathematics.

Those are the clearly understood properties of bodies in general.

What about less clearly understood properties (for example light or sound or pain), and properties of particular bodies (for example the size or shape of the sun)?

Since God is not a deceiver, it means I have the ability to correct any falsity in my opinions. Everything that is ‘taught by nature’ certainly contains some truth.

‘Nature’ refers to:

  • God himself or
  • the ordered system of created things established by him.

My own nature is simply the totality of things bestowed on me by God.

My own nature teaches me that:

  • I have a body
  • there is something wrong with that body when I feel pain
  • when I am hungry or thirsty it needs food and drink
  • and so on

Nature also teaches me, through these sensations of pain, hunger, thirst and so on, that I (a thinking thing) am not merely in my body as a sailor is in a ship.

  • Rather, I am closely joined to it, intermingled with it, that it and I form a unit.
  • This makes me feel pain when the body was hurt yet perceive the damage in an intellectual way, like a sailor seeing that his ship needing repairs.

When the body is hungry, I would intellectually understand this fact instead of (as I do) having confused sensations of hunger and thirst.

These sensations are confused mental events that arise from the union – the intermingling, as it were – of the mind with the body.

Nature also teaches me that various other bodies exist in the vicinity of my body, and that I should seek out some of these and avoid others.

Also, I perceive by my senses a great variety of colours, sounds, smells and tastes, as well as differences in heat, hardness and so on; from which I infer that the bodies that cause these sensory perceptions differ from one another in ways that correspond to the sensory differences, though perhaps they don’t resemble them.

Furthermore, some perceptions are pleasant while others are nasty, which shows that my body – or rather my whole self insofar as I am a combination of body and mind – can be affected by the various helpful or harmful bodies that surround it.

However, some of what I thought I had learned from nature really came not from nature but from a habit of rushing to conclusions. Those beliefs could be false.

Here are a few examples: that if a region contains nothing that stimulates my senses, then it must be empty; that the heat in a body resembles my idea of heat; that the colour I perceive through my senses is also present in the body that I perceive; that in a body that is bitter or sweet there is the same taste that I experience, and so on; that stars and towers and other distant bodies have the same size and shape that they present to my senses.

‘Nature’ does not mean the totality of what God has given me.

From that totality I am excluding things that belong to the mind alone, such as my knowledge that what has been done can’t be undone (I know this through the natural light, without help from the body).

I am also excluding things that relate to the body alone, such as the tendency bodies have to fall downwards.

My sole concern here is with what God has given to me as a combination of mind and body.

My ‘nature’, then, in this limited sense, does indeed teach me to avoid what hurts and to seek out what gives pleasure, and so on.

But it doesn’t appear to teach us to rush to conclusions about things located outside us without pausing to think about the question; for knowledge of the truth about such things seems to belong to the mind alone, not to the combination of mind and body.

So, although a star has no more effect on my eye than a candle’s flame, my thinking of the star as no bigger than the flame does not come from any positive ‘natural’ inclination to believe this; it’s just a habit of thought that I have had ever since childhood, with no rational basis for it.

Similarly, although I feel heat when I approach a fire and feel pain when I go too near, there is no good reason to think that something in the fire resembles the heat, or resembles the pain. There is merely reason to suppose that something or other in the fire causes feelings of heat or pain in us.

Again, even when a region contains nothing that stimulates my senses, it does not follow that it contains no bodies.

I now realize that in these cases and many others I have been in the habit of misusing the order of nature. The right way to use the sensory perceptions that nature gives me is as a guide to what is beneficial or harmful for my mind-body complex; and they are clear and distinct enough for that.

But it is a misuse of them to treat them as reliable guides to the essential nature of the bodies located outside me, for on that topic they give only very obscure information.


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