How do we see (and hear and smell) the world? Most of us uncritically suppose that physical objects around us are more or less as we perceive them to be, but there are problems with this commonsensical notion that have led many philosophers to question whether we in fact observe the outside world directly. In their view we only have direct access to inner “ideas,” “impressions” or (in modern terms) “sense data.” The 17th-century English philosopher John Locke used a celebrated image to elucidate this. Human understanding, he suggested, is like “a closet wholly shut from light, with only some little openings left, to let in external visible resemblances, or ideas of things without.”
But there is a big snag with Locke’s conception. We may suppose that the ideas that enter the closet are more or less faithful representations of things outside it, but in the end it is a matter of inference that these inner representations correspond closely to external objects—or indeed to anything at all. Our ideas, which are all that we have direct access to, form an impenetrable “veil of perception” between us and the outside world.
In his 1690 Essay Concerning Human Understanding Locke gave one of the fullest accounts of what are known as “representational” models of perception. Any such model that involves intermediate ideas or sense data drives a wedge between us and the external world, and it is in the fissure so formed that skepticism about our claims to knowledge takes root. It is only by reestablishing a direct link between observer and external object that the veil can be torn and the skeptic vanquished. So, given that the model causes such problems, why adopt it in the first place?
In modern terms, Locke’s model of perception is called “representative realism,” in distinction to the “naïve” (or “common-sense”) realism to which all of us (even off-duty philosophers) adhere most of the time. Both views are realist, in that they are committed to an external world that exists independently of us, but it is only in the naïve version that redness is thought of as a simple property of the tomato itself. Although Locke may have given the classic statement of the theory, the representational model of perception did not start with him. It is sometimes disparagingly referred to as the “Cartesian theater,” because in Descartes the mind is effectively a stage on which ideas (perceptions) are viewed by an inner observer—the immaterial soul. The fact that this inner observer, or “homunculus,” itself appears to require an inner observer of its own (and so on to infinity) is but one of the objections raised against the theory. Nevertheless, in spite of these objections, the model has remained highly influential.
Primary and secondary qualities The unreliability of our perceptions forms an important part of the skeptic’s weaponry in attacking our claims to knowledge. The fact that a tomato can look anything from red to black depending on the lighting conditions is used by the skeptic to cast general doubt over our senses as a reliable pathway to knowledge. Locke hoped that a perceptual model in which inner ideas and outer objects were separated would disarm the skeptic. His argument depended crucially on a further distinction—between primary and secondary qualities.
The redness of a tomato is not a property of the tomato itself but a product of the interaction of various factors, including certain physical attributes of the tomato such as its texture and surface structure; the peculiarities of our own sensory system; and the environmental conditions prevailing at the time of the observation. These properties (or rather nonproperties) do not belong to the tomato as such and are said to be “secondary qualities.”
“No man’s knowledge … can go beyond his experience.”
John Locke, 1690
At the same time, a tomato has certain true properties, such as its size and shape, which do not depend on the conditions under which it is observed or indeed on the existence of an observer at all. These are its “primary qualities,” which explain and give rise to our experience of the secondary qualities. Unlike our ideas of secondary qualities, those of primary qualities (Locke thought) closely resemble the physical objects themselves and can afford knowledge of those objects. For this reason it is with primary qualities that science is largely concerned, and crucially, with respect to the skeptical challenge, it is our ideas of primary qualities that are proof against the skeptic’s doubts.
Today Berkeley’s immaterialist theory is seen as a virtuosic if eccentric metaphysical tour de force. Ironically, though, Berkeley regarded himself as the great champion of common sense. Having deftly exposed the pitfalls in Locke’s mechanistic conception of the world, he proposed a solution that seemed obvious to him and which dismissed all the dangers at a stroke, banishing both skeptical and atheistic concerns. It would be even more galling for Berkeley that his place in the popular imagination today is limited to Samuel Johnson’s famous though uncomprehending rebuttal of immaterialism, recorded in Boswell’s The Life of Samuel Johnson: “Striking his foot with mighty force against a large stone, [he exclaimed] ‘I refute it thus.’”
Stuck in Locke’s closet One of Locke’s earliest critics was his Irish contemporary, George Berkeley. Berkeley accepted the representational model of perception in which the immediate objects of perception were ideas, but he recognized at once that far from defeating the skeptics, Locke’s conception risked surrendering all to them. Holed up in his closet, Locke would never be in a position to check whether his supposed “resemblances, or ideas of things without” actually resembled the external things themselves. He would never be able to lift the veil and look on the other side, so he was trapped in a world of representations and the skeptic’s case was made.
“It is indeed an Opinion strangely prevailing amongst Men, that Houses, Mountains, Rivers, and in a word all sensible Objects have an Existence Natural or Real, distinct from their being perceived.”
George Berkeley, 1710
Having lucidly set out the dangers of Locke’s position, Berkeley came to an extraordinary conclusion. Rather than tear through the veil in an attempt to reconnect us with the external world, he concluded instead that there was nothing behind the veil to reconnect with! For Berkeley, reality consists in the “ideas” or sensations themselves. With these, of course, we are already fully and properly connected, so the dangers of skepticism are evaded, but at quite a price—the denial of an external, physical world!
According to Berkeley’s idealist (or immaterialist) theory, “to exist is to be perceived” (esse est percipi). And so do things cease to exist the moment we stop looking at them? Berkeley accepts this consequence, but help is at hand—God. Everything in the universe is conceived all the time in the mind of God, so the existence and continuance of the (nonmaterial) world is assured.
the condensed idea
What lies beyond the veil?
| Timeline | |
|---|---|
| c.375BC | Plato’s cave |
| AD1644 | Cogito ergo sum |
| 1690 | The veil of perception |
| 1981 | The brain in a vat |