Descartes' View of Sense Perception

Introduction - Descartes' Thesis:

Some have suggested that René Descartes argues that sense perception relies on the mind rather than on the body. Descartes asserts that we can know our mind more readily than we can know our body. In support of this idea he gives the example of a piece of wax which is observed in its solid form and its liquid form. After pointing out the difficulties of relying on the senses of the physical body to understand the nature of the wax he makes this claim: [P]erception ... is neither a seeing, nor a touching, nor an imagining. ... [R]ather it is an inspection on the part of the mind alone (Section 31). ¹ This quote is perhaps the most direct statement of the author's thesis on this subject.

I contend that, based upon the arguments presented in the Second Meditation, Descartes shows that we can use our senses to help us understand the true nature of things, but the senses alone are inadequate to determine truth (since they are often deceived), and that all that may be known with certainty (truth) are those things we know by our judgment, thinking, and understanding of them in our minds. Descartes' argument does not necessarily reject any role of the senses in the process of understanding.

Steps of the Argument:

Descartes began his argument in the First Meditation by questioning or calling into doubt everything that he knew. After examining all the things he thought he knew about himself and the world he concluded (the details of that argument are beyond the scope of this essay) that the only thing he knew with absolute certainty is that I am, I exist (Section 25). Having established the fact that he has a real existence of some kind he then said But I do not yet understand sufficiently what I am--I who necessarily exist (Section 25).

This line of questioning (again the details of that argument are not necessary to this discussion) led him to draw this conclusion: I am therefore precisely nothing but a thinking thing (res cogitans) ²; that is, a mind (mens), or intellect (intellectus), or understanding, or reason (ratio) -- words of whose meanings I was previously ignorant. Yet I am a true thing and am truly existing; but what kind of thing? I have said it already: a thinking thing (Section 27). Note here that Descartes equates mind, intellect, understanding, reason, and soul with thinking ³ .

Having assured himself that he exists and that the essential nature of his self includes at least the capacity to think he then explored the question What else am I? (Section 27) and reached this conclusion: But then what am I? A thing that thinks (res cogitans). What is that? A thing that doubts (dubitans), understands (intelligens), affirms (affirmans), denies (negans), wills (volens), refuses (nolens), and that also imagines (imaginans) and senses (sentiens) (Section 28). Descartes acknowledges that thinking includes doubt, understanding, affirmation, denial, will (volition), refusal, imagination, and senses .

Descartes has said the senses (sentiens) are a part of the process of thinking (cogitans), now he clarifies what he means when he speaks of the senses in the remainder of the text. Yet I certainly do seem to see, hear, and feel warmth. This cannot be false. Properly speaking, this is what in me is called 'sensing (sentire).' But this, precisely so taken, is nothing other than thinking (cogitare) (Section 29). While it may appear that Descartes is attempting to redefine a term in common usage in a manner which would support his argument, it could also be argued that this clarification was intended only to point out that even if it were true that I do not in reality have a physical body (as he assumed was possible in an earlier part of the argument which led to the conclusion: I think, therefore I exist) this seeming to "see, hear, and feel warmth" would serve the same function in the process of cogitation as the actual physical senses would have if my body is real.

From these considerations I am beginning to know a little better what I am. But it still seems (and I cannot resist believing) that corporeal things--whose images are formed by thought, and which the senses themselves examine--are much more distinctly known than the mysterious 'I' which does not fall within the imagination (Section 29). Now the thought occurs to Descartes that perhaps I use my mind to understand abstract things (like the nature of my existence), but it is with the senses that we explore and examine physical things. Then he uses the example of a piece of wax to show that even physical things can only be clearly understood by inspecting them with the mind (and not relying solely on the senses). I will not quote his entire development of the wax example, but summarize it thus:

Observe a piece of wax. It has a distinctive feel, odor, sound, taste, size, color, and temperature (Section 30).
As the wax is heated each of those sensory attributes changes dramatically or is lost altogether (Section 30).
Relying only on the physical senses would lead to the conclusion that the wax in its original form is a different substance than the wax in its later form, yet no one claims that both are not the same substance (Section 30).
If the sensory elements of the wax are unreliable in helping us understand the wax, what are the essential non-sensory characteristics of wax? It is something extended ⁴ , flexible, and mutable (Section 31).
How do I understand that it is extended, flexible and mutable? Perhaps it is by my imagination. I cannot imagine all of the infinite variety of forms the wax might take, so imagination is not responsible for my understanding of wax (Section 31).

If sensory perception and imagination have been eliminated, the only possible explanation is that my mind (mens) is responsible for my understanding of wax in the various forms it can take. But I need to realize that the perception (perceptio ⁵) of the wax is neither a seeing ( visio), nor a touching (tactio), nor an imagining (imaginatio). Nor has it ever been, even though it previously seemed so; rather it is an inspection (inspectio) on the part of the mind (mentis) alone. This inspection can be imperfect and confused, as it was before, or clear and distinct, as it is now, depending on how closely I pay attention to the things in which the piece of wax consists (Section 31). So even though my senses have revealed the wax to me in different forms my mind has always, by processes independent of my senses, understood the essence of the wax and that it may be presented by the senses in differing ways. Note that Descartes does not state that the senses have no value, only that understanding is the function of the mind rather than of the senses. It might be said that if one hopes to understand something (even a physical thing) it must be done by the mind rather than relying only on the senses.

But meanwhile I marvel at how prone my mind is to errors.... For we say that we see the wax itself, if it is present, and not that we judge it to be present from its color or shape (Section 32). In our common speech we turn around the relationship between cognition and sensory perception. Similarly, Descartes points out that I might look out the window and say that I see a person walking by when all I have seen is a hat and some clothing (which may be concealing a robot). I use my mind to form a judgment that what I saw was a person, even though I did not actually see a person (Section 32). Note that nothing in his argument denies the existence of the sensory input, in fact the senses provide the raw material for the operations which the mind performs.

When did I have a more perfect knowledge of the wax? Only after I have diligently examined both what the wax is and how it is known. ... But indeed when I distinguish the wax from its external forms, as if stripping it of its clothing, and look at the wax in its nakedness, then, even though there can still be an error in my judgment, nevertheless I cannot perceive it thus without a human mind (Section 32). Here Descartes is still speaking of a role for the senses (how it is known, and its external forms) in forming a proper perception of the wax.

Furthermore, if my perception of the wax seemed much more distinct after it became known to me not only on account of sight or touch, but on account of many reasons, one has to admit how much more distinctly I am now known to myself. For there is not a single consideration that can aid in my perception of the wax or of any other body that fails to make even more manifest the nature of my mind (Section 33). Once again Descartes speaks of the wax in terms of both the senses and reason.

For since I now know that even bodies are not, properly speaking, perceived by the senses or by the faculty of imagination, but by the intellect alone (solo intellectu percipi), and that they are not perceived (percipi) through their being touched or seen, but only through their being understood, I manifestly know that nothing can be perceived more easily than my own mind (Section 34). It might seem that Descartes wants to abandon any role for the senses now that he has arrived at his conclusion, but this summary is intended not to say that sensory perception has no value, rather cogitation has greater value. His point is that although it might seem easier to understand things which can be directly observed by the senses, the example of the wax demonstrates that thinking (inspection by the mind) is the better way to know physical objects which, if they have real existence, exist outside the mind; and consequently even more so the mind itself and it contents.

Critique and Conclusion:

The example of the wax is an effective one to demonstrate the difficulty of relying upon our senses for an understanding of the world around us. As a part of the larger argument, that I can know myself better than I can know any thing which I know by my senses, it serves to demonstrate that the things we thought we knew most clearly because we can know them through our senses, we really can only know properly by using our minds.

We can use our senses to help us understand the true nature of things, but the senses alone are inadequate to determine truth (since they are often deceived). All that may be known with certainty (truth) are those things we know by our judgment, thinking, or understanding of them in our minds. The only reliable authority in determining what is true and real is the mind.

Descartes' arguments do not support the conclusion that "sense perception relies on the mind rather than on the body" as was suggested in the instructions for this assignment. Based on the reasoning presented above I would suggest the premise be revised to read: sense perception relies on the mind more than on the body.

WORKS CITED

Descartes, René. Meditations on First Philosophy: in Which the Existence of God and the Distinction of the Soul from the Body are Demonstrated . Trans. Donald A. Cress. Indianapolis: Hackett Publishing, 1993.

Descartes, René. Meditations on First Philosophy in Which the Existence of God and the Distinction Between the Mind and Body are Demonstrated . Trans. Elizabeth S. Haldane (1911). Online. Internet. 22 Mar. 1997. The Internet Encyclopedia of Philosophy (copyright 1996, James Fieser). Available: http://www.utm.edu/research/iep/text/descart/des-med.htm

Descartes, René. Meditations on the First Philosophy in Which the Existence of God, and the Real Distinction of Mind and Body, are Demonstrated . Trans. John Veitch (1901). Online. Internet. 22 Mar. 1997. Available: http://philos.wright.edu/DesCartes/MedE.html .

Descartes, René. MEDITATIONES De Prima PHILOSOPHIA, In quibus Dei existentia, & animae humanse à corpore distinctio, demonstrantur . Online. Internet. 22 Mar. 1997. Available: http://philos.wright.edu/DesCartes/MedL.html

[1] Descartes, René. Meditations on First Philosophy: in Which the Existence of God and the Distinction of the Soul from the Body are Demonstrated . Trans. Donald A. Cress. Indianapolis: Hackett Publishing, 1993. Unless indicated otherwise, all quotations will be from this translation. Section numbers are references printed in the margins of some current translations of this text. They are actually references to page numbers in the Adam and Tannery edition (1897-1913) of the original Latin text. (Where paragraph numbers are used here, they will be cited as: II:2; indicating Meditation 2, paragraph 2 in the Latin text.)

[2] Throughout this essay italicized words or phrases in parentheses are used to indicate the Latin words behind the English word or phrase in the translation.

[3] It is interesting that both the Veitch and the Cress translations seem to ignore the Latin word animus which Descartes listed between mens and intellectus . Haldane translates it here as "soul." Earlier in Section 27 all three translators used "soul" for the Latin animae , and in Section 26, all three translators render animam and anima as "soul".

[4] In physics, the concept of extension denotes that property by which a physical body occupies space. In this connection Descartes's description of his physical body (in comparison with his soul) is helpful: "[B]y 'body,' I understand all that is capable of being bounded by some shape, of being enclosed in a place, and of filling up a space in such a way as to exclude any other body from it; ..." [followed by other features not related to extension]. (Section 26)

[5] Perceptio : a related word perceptione in I:11 is translated as knowledge, or perception. In II:5 vel odoratu percipi is translated as [the sense of] smell. In II:7 percipiat is translated perceive or know. In II:11 perceptiones is translated perceptions, notions, or ideas. In II:12 solâ mente percipere is rendered "it is the mind alone which perceives it" (Veitch), "it is my mind alone which perceives it" (Haldane), "I perceive it through the mind alone" (Cress). In II:14 perfectius evidentiusque percipiebam is translated "evident and perfect conception" (Haldane), "clearer and more perfect perception" (Veitch), and "perceived more perfectly and evidently" (Cress).