If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Epistemology: Paradoxes of Perception #1 (Argument from Illusion)

In this video, Dr. Eugen Fischer (UEA) presents the ‘argument from illusion’. This argument appears to refute our common-sense conception of perception (seeing, hearing, etc.). Together with parallel arguments, it raises the problem of perception that has been a lynch-pin of Western philosophy, since the mid-18th century.

Speaker: Dr. Eugen Fischer, Associate Professor of Philosophy, University of East Anglia.

Want to join the conversation?

  • leafers ultimate style avatar for user Nitaicapp
    The video claims that we cannot be aware of the coin when we see an elliptical patch, because the "actual" coin is round, but the common sense answer should be the coin is a 3 dimensional object. When you see it from a certain angle it looks circular, but what makes that angle more valid then the angle that makes it appear elliptical? And if we aren't trusting our senses anymore, how can we make ANY assumptions about the physical world around us? How do we know the pencil DOESN'T bend when it enters the water? How do we know tables DON'T shrink when we move away from them? The video uses evidence gathered by sense perception and common sense to prove that we can't rely on sense perception and common sense, seemingly defeating itself in the process. Is there anything wrong with this conclusion, or am I missing something?
    (5 votes)
    Default Khan Academy avatar avatar for user

Video transcript

(intro music) Hi! I'm Eugen Fischer, senior lecturer in philosophy at the University of East Anglia. Today, we will look at some paradoxes about perception, known as "arguments from illusion." These arguments ask us to consider cases of non-veridical perception, where something appears different than it is. For example, when we look at round coins sideways, they appear elliptical. Similarly, when seen from a greater distance, a man may seem less than half as tall as another man of roughly equal height. Or consider the phenomenon known as "refraction." When a straight straw is partially immersed in water, it looks bent. All of these facts are familiar from daily life. None of them is normally contested. But these familiar facts seem to have a striking consequence. They seem to imply that we are cut off from the physical objects around us by a veil of experience within us. The eighteenth-century philosopher David Hume drew this consequence very swiftly when reflecting on another relevant fact: as we all know, the table look smaller and smaller to people the further away the move from it. Hume observes that the table we see seems to get smaller as we move away from it, yet there is no change in the size of the real table, which is made of wood and stands in the parlor, regardless of whether we look at it or not. Hume immediately infers that we cannot be aware of this unchanging, real table, and therefore must be aware of something else. He concludes that thing we see is an image of the table, whose size does change as we move away from the table. This image then is present to us in our minds. In other words, when you look at the table, you are only aware of a mental image, not of the physical table. To unpack this rather swift but historically influential argument, let's have a closer look at the case of the round coin that appears elliptical to you when you look at it sideways. What exactly are you aware of in this case? Describe your experience, rather than the objects around you. Describe what you are aware of, without making any judgment about the physical object you're facing, without judging that object's shape, or size, or color, or any other property of it. That the right thing to say then, it seems, is that you're aware of an elliptical, golden patch. This judgment is often called the "phenomenal judgment." The first step the argument elicits such phenomenal judgments about cases of non-veridical perception, like that of the coin or Hume's table. The second step has us figure out what kind of thing we're then aware of. What could that elliptical patch be? It cannot be the coin, because the coin is round and not elliptical. So you're clearly aware of something other than the coin. Hume called this other thing an "image." A now more common, and more neutral term, is "sense-datum." Now continue to look in the direction of the coin. How many different things do you see? How many different things can you direct your attention at and say that you are aware of? Clearly, you cannot first direct your attention at something elliptical and then shift your attention elsewhere to become aware of something else that could be the coin. So you are aware only of one thing, not of two. We already concluded that you are aware the sense-datum. Therefore, you cannot be aware of the coin too. At any rate, not in the same way or sense. But of course you are aware of the coin in some sense. You know perfectly well that you are looking at a coin rather than, say, a marble or a dice. Proponents of the argument from illusion therefore commonly called the cautious conclusion that the subjective sense-datum is the only thing you are directly aware of when looking at the coin sideways. At the same time, you may be indirectly aware of the physical object, namely, in virtue of being directly aware of the sense-datum. So far, we have rehearsed the first half of the argument. The second half then generalizes from the particular case of non-veridical perception to all cases of perception. This generalizing step builds on the observation that sense data and physical objects are the most radically different kinds of things. For a start, the sense-datum is rather less stable than the coin. The color patch changes its shape the moment you move, while the coin retains its shape. The sense-datum also vanishes the moment you close your eyes, while the coin vanishes only the moment it gets melted down, or some other major physical mishap occurs to it. So the sense-datum and its properties depend upon you, the observer, in ways in which the physical object and its properties do not. Sense data are subjective, ever-changing, and fleeting, like the flickering of a candle or its dying smoke. Physical objects, by contrast, are objective and stable, like solid tables and hard coins. the intuitive key assumption now is that our awareness of such radically different things should constitute qualitatively different experiences. We should be able to tell from the subjective quality of our experience whether we are aware of a sense-datum or of a physical object. But compare. Have a look at this pencil, which is partially immersed in water. To most people, it seems bent. If you are like them, you are now directly aware of a sense-datum or color patch, which actually is bent. And now look at the pencil in the dry, when it looks as straight as it actually is. Can you tell any difference between the subjective quality of one experience and the other? Does one scene look, say, follier to you, or less clear, or more vivid? Philosophers who find they cannot grow aware of any such difference like to conclude that we must be aware of the same kind of thing in both cases. So, if we are directly aware of a subjective sense-datum in the case of non-veridical perception, such a sense-datum is what we are directly aware of also in the case of veridical perception. When we use our eyes, all we are ever directly aware of are subjective sense-data. By sight, we are never directly aware of physical objects. As we look around ourselves, we are cut off from the physical objects in our environment by a veil of subjective sense-data. Other variants of the argument establish analogous conclusions about the other senses: hearing, smell, taste, and touch. Some other arguments, including arguments from hallucination, lead from different premises to the same conclusions. These conclusions seem to clash with common sense. Surely, when we look at tables and chairs, we see these public, stable, physical objects without further ado. Surely, these objects are not blocked from view by subjective, ever-changing objects of awareness. Surely, we can just see tables and chairs, without having to infer their presence around us from subjective images, sense-data, or what have you. By leading to a conclusion that clashes with our common sense conception of perception, all these arguments confront us with what is often simply called the "problem of perception." We don't doubt that things sometimes appear elliptical, yellow, bitter, or rough when they actually are round, white, sweet, or smooth. The present argument suggests this implies that we cannot just see or hear, smell or taste, or feel the things around us This raises the problem: how is it possible for us to just see, or otherwise perceive, the things in our physical environment if these things often appear different than they are? Subtitles by the Amara.org community