1. Empiricism and sense data

2. Realism

3. The pragmatic use of sense data

We find Descartes writing in his laboratory book describing each step of his experiment and the results accomplished. He is, as any good scientist, very detailed in his exposition so that other scientists (us) may understand and duplicate his experiment. We will read directly from his lab book (The Meditations on First Philosophy). However, I will jump in with questions and commentary as the situation arises.

Let me again describe the conditions he sets up for his "lab." Descartes is sitting by a warm fire in a retreat away from the city. He is wearing comfortable clothing and has informed his innkeepers not to bother him unless summoned. He begins his "meditations." He turns to thoughts in his mind.


"It is now some years since I detected how many were the false beliefs that I had from my earliest youth admitted as true, and how doubtful was everything I had since constructed on this basis; and from that time I was convinced that I must once for all seriously undertake to rid myself of all the opinions which I had formerly accepted, and commence to build anew from the foundation, if I wanted to establish any firm and permanent structure in the sciences. But as this enterprise appeared to be a very great one, I waited until I had attained an age so mature that I could not hope that at any later date I should be better fitted to execute my design." "Now for this object it is not necessary that I should show that all of these" (ideas of a certain kind) "are false --I shall perhaps never arrive at this end. But inasmuch as reason already persuades me that I ought no less carefully to withhold my assent from matters which are false, if I am able to find in each one some reason to doubt, this will suffice to justify my rejecting the whole. And for that end it will not be requisite that I should examine each in particular, which would be an endless undertaking; for owing to the fact that the destruction of the foundations of necessity brings with it the downfall of the rest of the edifice, I shall only in the first place attack those principles upon which all my former opinions rested." "All that up to the present time I have accepted as most true and certain I have learned either from the senses or through the senses; but it is sometimes proved to me that these senses are deceptive, and it is wiser not to trust entirely to any thing by which we have been once deceived." (From The Philosophical Works of Descartes, "Meditation I," trans. by E.S. Haldane and G.R. Ross (Cambridge: Cambridge University Press, 1931))

Whoa! Hold on for a minute Descartes. There is a lot of material here and you went pretty fast. We need to proceed step by step so that we can see just how much trouble we are getting into. Step by step, what does Descartes say?

First of all, Descartes tells us (in 17th century double-talk) that he is seeking a firm and permanent structure in the sciences; in other words, he is looking for some truth which will establish the sciences as enterprises in their own right which do not threaten the Church. In fact, since Descartes is a believer, his ultimate goal is to base the sciences on the conception that God created a rational world. Nevertheless, he does not want to state precisely to the Church that he is going to set the sciences free, even if God is still the final answer. But, let's wait for more to come down the road to see how he accomplishes this task.

Next, he says that we should doubt things according to the probable truth of things in their class; that is, if there is any suspect item of a class of items, then the whole class is questionable. This rule of thumb, as we will see, is a time-saver. Here is an example to help us see what Descartes is after. Suppose we have a barrel of apples. We draw out one and it is good. We draw out another and it is good. But, the third apple we remove is rotten. Why draw another apple, Descartes would ask? If we know that there is one rotten apple in the barrel, there could be more. We cannot trust that the apples in this barrel are good, and if this barrel contains all the apples that there are, then all apples constitute a suspect class. Likewise with certain kinds of ideas; if any idea of a kind is suspect, then all ideas of that kind are suspect. Remember, we are after the truth or an absolutely good barrel of apples. Any one rotten (even tainted) apple in a barrel makes the whole barrel suspect; any one questionable idea makes the rest of its kind suspect and thus not capable of being called knowledge.

Then, Descartes begins his experiment. The first class of ideas he subjects to doubt are the ideas he gains from the senses. Let us call this kind or class of ideas, SENSE DATA. Let's do an experiment in detail with respect to sense data.

Right now you are reading this material. You see a white page with black print on it. At the same time you are probably aware of the colors of the object in the room. You may see the colors of your pants (skirt), shirt, shoes, walls, and more. All of these qualities you sense of the world come through the sense organs; you see, smell, hear, touch and taste the world. You come into contact with the world through sense data. You sense that your shoes are brown, your shirt red, the pages of the book cool, the air full of the aroma of the banana you just ate, and the room noisy from the air-conditioner and so on. You claim to know all these "facts" about the world because you trust your senses. After all, "seeing is believing."

1. Why empiricism will not do; sense data cannot give certainty.

Empiricists think that knowledge derives from sense data. Knowledge comes from the mind operating on the data that enter through the senses. The mind is like an empty closet before sense data begins to fill it up. Operating on that data which comes in, the mind discovers associations among ideas from which knowledge derives. Should we ask you, "Is your shirt red?" you could respond, "Yes, it is red, because I and all of us can see that it is red. Our ideas in our minds are data which tell us the truth about the world." Besides, who in their right mind would doubt the facts or truths of sense data? If we see a red shirt, we do not doubt that there is really a red shirt in the real world that our ideas represent. Who would doubt that we have true ideas of the world around us? Who would doubt that if we see green grass that the grass is green?

Well, Descartes does, and he does it in one fell-swoop. Let's use his method to do some experimentation to reach the same conclusion he does.

Go to the sink and put one hand in a basin of hot water, the other in a basin of cold water. Now, place both in the same basin filled with room-temperature water. The "hot-water hand" will sense the room-temperature water as cold; the "cold-water hand" will sense the same water as hot. But, which sensation is the right one? You cannot say given the sense data you are actually experiencing, for the data are radically different. Thus, you can doubt the truth or "facts" gained through the sense of touch.

Listen to an airplane going by. The pitch of the engines sounds much higher before it reaches your position than it does when it passes you. Which pitch is the correct rendition of the rpm's of the engines? You cannot say what is the true pitch because the sounds are different. Thus, you can doubt the truth or "facts" gained through the sense of hearing.

Smell and taste can be confused by extremes. Try eating a peppermint candy before tasting some grapefruit. The grapefruit will taste so sour that you can hardly stand it. Yet, had you begun with the grapefruit, it would have been "fruity" and acceptable; the peppermint candy afterward would have been sickly sweet. So, taste and smell sense data can be doubted as to revealing the truth about states of the world. Besides, it just sounds strange to say that a property of a lemon is its sourness. If there were no taste buds on any animals' or humans' tongues, would a lemon itself be sour? Don't think so.

Data from sight is easily doubted. Railroad tracks appear to meet in the far distance, but they do not no matter how far you walk down the tracks. Sticks appear to be bent when placed half-way in a pool of water, but they are not. Here's a practical tip, never buy a car at night under artificial light; the color will be different in daylight. But, which is the "true" color? We may doubt the data given to us by our eyes.

To sum up, it looks like Descartes is right. Not one of our senses gives us data that we can call absolutely reliable or certain. If all sense data can be doubted as to its truth value, then knowledge which is certain --which is indubitable-- cannot come from the senses. We have pulled out a bad apple from each sense "barrel." Hence, all the data from the senses are suspect.

This conclusion is disturbing, for most of us really do trust our senses to give us reliable information about the world; most of us think that "seeing is believing." Such a belief puts us into the camp of empiricists who are also realists. Realists think that there is a real world of objects which we can know; that is, there is an external world to our minds and we can know facts about that world. A simple empirical realist claims that there is an external world which we can know through our senses AND our ideas of that world correspond ADEQUATELY (the ideas are exact copies of the real things) to the objects in the world. If I have ideas of the world that come through the senses, they are precisely informative about the object I see. If I see a deep red apple, then there really is an apple of that deep red color out there in the world.

So far, Descartes is a realist (there is a world apart from our ideas), except that he has denied that we can know adequately this world through sense data (so, he isn't a simple empirical realist). The real world just may be different, very different, from how it appears to us. Remember, Descartes' situation is not very different from our own. Consider what our scientist friends tell us. Apples aren't red at all; the light photons which hit our eyes have been affected by the atomic structure of the skin of the apple so that a certain wavelength of light is reflected back to our eyes. That wavelength has no color but can produce color in our minds somehow. The sound of the airplane is no more than air being compressed at various levels and times. There is no "sound" in the world, only air being compressed. The compressed air is translated into sound by our hearing mechanisms and brain. Ask yourself, "Why are all the movie scenes (check out Star Wars), which have explosions in space accompanied by a tremendous noise, impossible?" The answer is that there is no air (or gases) in space to be compressed; consequently, there is NO noise in space. The water that you felt in the sink. What felt warm? Was it the water itself or the speed of the movement of the atoms making up the water? The latter. You did not sense any real property of water, only the movement of the atoms, which was translated into a certain kind of sense data, warmness. Water is neither hot nor cold in itself; the atoms are merely moving faster or slower. Sometimes our sensory mechanism of touch can be "broken" by extremes going beyond its capability of translation. Try holding a piece of dry ice (solid CO2). Burns, doesn't it! The same sorts of faults can be pointed out about all of our sensory systems. Descartes looks to be right. The senses don't tell us the truth about the things we sense.

But, Descartes is going to push his criticism of empiricism and realism to a breaking point which will leave us in a much more uncomfortable position than which we now find ourselves. Let us continue with his experiment and see what happens.

Remember that our laboratories are our minds and the experimental subjects our ideas. We are examining the nature of certain ideas, sense-data, which are IN our minds. That is to say that the ideas (sense data) in our minds are purportedly ideas OF the things in the world; they are NOT the things themselves, but representations of them. Let me help with an analogy.

Think of your mind as being the screen of a video theater. Now, this is an unusual video theater, because it is a smell, feel, touch, hear, taste-o-rama also. That is, sensations besides sight are in the theater as if they were on the screen. You are in the middle of the theater, but it is all dark around and you can only see yourself by looking at the screen. For example, were you to hold out your hand you would see it appear on the screen in front of you. You cannot sense yourself in any way sitting in the theater anymore than you can see the lens of your eye while looking through it. Remote cameras or sensory mechanisms which are external to the theater and which view or sense external objects put every item that appears on the screen there. What you are in contact with first and foremost are the images on the screen (the ideas in your mind). You are not in contact first-hand with external objects, for they are viewed by your sensing mechanisms which produce the images on our screen --much the same way a camcorder produces images on a terminal and you are watching the terminal. What is important to consider is that there are no doors or windows to the theater; you can never get outside to look at the world itself. All you have to go on are the images on your screen.

Suppose that you decide to direct your camcorder (eyes) to view an object resting on the nearby table. There appears on your screen the image of a red apple. The question to ask is, "How do I know that the apple out there is the color red of the apple on the screen?" You cannot peek out a window and compare the image on the screen with the real external apple, for you can never "get out of your mind." As a matter of fact, things get more complicated as you watch the image on your screen as the light is reduced. The color of the apple changes to a darker red. When there is very little light at all, the apple looks black. Does the real apple change color? You would want to say "No," but there is no reliable way to tell. Just answer this question, "Which color of all the ones you sense of the apple is the real color and how do you know?"

The gist of the experiment is that we must give up simple empirical realism. There is no way to tell what color is the correct color of any object. The thesis, which says that ideas in our minds correspond exactly to the real objects of the world, can be doubted. But, that's just the start of the trap Descartes has sprung on empiricists.

It may be that the objects of the real world do not have any color at all but merely cause the representations of them (sensations or ideas) on our screens to appear in color. This point may be "confirmed" by going to your chemistry or physics professors. Ask them about the basic constituents of the physical or (their) real world. More than likely they will tell you about peculiar things called quarks, positrons, neutrinos, electrons and so on. Ask them if any one of these basic physical items has a color such as the red which belongs to the apple. The reply will probably be along these lines. "No. Sub-atomic items have no qualities. What you saw as red was a wave-particle (a photon) which stimulates the rods and cones of your retina, which in turn produces a 'chemical current' along the optic nerve, which then excites a wide range of brain nerve cells. There is no color anywhere in this sequence or, in fact, in the atomic world. The idea of the red apple is an epiphenomenon (an apparition or phantasm) which is caused by the neurons firing." So, we are left to conclude that color appears IN THE MIND (on the screen), but that color does not exist in the world of physical entities, not even in our brains. Microsurgery could never reveal a color (the red of the apple) in our brains, even during the moment we are having the sensation of the color. The real world is radically different from the way we experience it; the real world is totally devoid of qualities.

I do not know about you, but conclusions such as the one we just reached are very distressing. I not only want to see red apples (have the representations or ideas in my mind), but I want to think of apples in the world as REALLY being red. A real world without color (or any qualities) would be awful to think about. But, that is what the physicists and Descartes indicate is the fact of the matter. At least, that is where our experiment has gotten us so far.

2. Why realism is in deep trouble.

Suppose you mention these concerns to your physics and chemistry professors. The answer you may get may be even more unnerving. "As a matter of fact," they might say, "the real world doesn't have ANY of the properties we would want to ascribe to it by an examination of our sensations of it. The real world is one of very small bundles of energy without definite form or dimension (sort of like cotton balls) whizzing around at incredible rates of speeds in mostly empty space in which they have only probable location. The real world is not hot or cold (that is merely the activity of the atoms), is not sweet or sour (that is merely ions in solutions), is not hard or soft (that is merely the nature of the bonds among the atoms), is not musical or with sound (that is merely wave-motion or compression of the atoms of a specific gaseous medium) and has no colors or defined shapes (that is merely photons interacting with the bundles of energy). In fact, much of what is there is impossible for us to sense. For example, infra-red, ultra-violet, gamma, x, and cosmic rays are undetectable by our senses, not to mention the positrons, electrons, quarks and so on. We will never be able to experience directly the subatomic world. Right now, were we to put a small TV unit inside our brains, it could receive the evening news because it can 'sense' wavelengths in the megahertz, whereas that information is unavailable to our senses directly. Sense data, our ideas of the world through the sense, do not represent ANYTHING ADEQUATELY about the real world. NOTHING on our screens is anything like what is really there external to us. The real world is entirely different from our experiences of it."

Now we are really in hot water! The analogy to a TV studio looks to be exactly the way our minds and bodies (with their sensing mechanisms) are set up. We are presented and come into contact ONLY with our ideas; we do not come into direct contact with the world at all; we know the EXTERNAL world only through the ideas on our screens (sense data in our minds) which are INTERNAL to those minds. What we experience first-hand are our ideas, not the world. The real world is somewhere outside our theaters and quite different from the REPRESENTATIONS (ideas) of it on our screens. Between the real world and our selves, there are our ideas of the real world; they re-present or image the world for us, but the re-presentations, though they are the best the senses can do, do not portray the true natures of the objects of the world at all. We SENSE a red apple and want to BELIEVE that there is a red apple in the world, but we cannot say that there really is a red apple in the real world; in fact, what really is out there, our scientist friends tell us, is not red (juicy, crispy, sticky, and so on) at all. Again, reality is radically different from our experiences of it.

3. Why do we have sense data at all if it cannot give knowledge?

A question may spring to mind at this point; why do we have sense data in the first place if sense data do not tell us anything true about the real world? Good question. Descartes gives an answer (elsewhere in his works) that sense data are functions that help us to survive in the world; sense data are like a pilot's instruments when he is flying in bad weather. His radar tells him what storm cells to fly around. His altimeter tells him how high he is. His air-speed indicator informs him that he is moving at a certain rate, and so on. Using his instruments, he can fly through the bad weather. Consider our situation. An apple smells bad when it is rotten. What is the real situation is a complex biological process of bacteriologically caused breakdown of complex molecules --but, it simply smells to us. Why? It is our bodies' quick short-cut mechanism to deep us from eating something that would harm us. Remember, the apple itself doesn't smell; it merely CAUSES the idea or sensation of a bad odor by releasing ketones into the air. At rock bottom, the qualities of sense data are survival mechanisms. It is in virtue of them that we don't get sick eating stinky apples.

OK, so sense data are survival mechanisms, but aren't they something more than just that? Can't we use sense data to obtain some working knowledge of the world? In fact, isn't that what our scientists do? Don't they experiment and use sense data to confirm their experiments? And when they experiment correctly, don't they come up with mathematical descriptions of the world (physical and chemical laws) which tell us a lot about the world? The answers to all these questions seem to be, yes.

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