[condensed from Chapter 3, The Embodied Mind, of “Philosophy In The Flesh”, by George Lakoff and Mark Johnson, published by Basic Books, 1999]
We are neural beings. Each human brain has 100 billion neurons and 100 trillion synaptic connections. It is common in the brain for information to be passed from one dense ensemble of neurons to another via a relatively sparse set of connections.
To take a concrete example, each human eye has 100 million light-sensing cells, but only about 1 million fibers leading to the brain. Each incoming image must therefore be reduced in complexity by a factor of 100. That is, information in each fiber constitutes a “categorization” of the information from about 100 cells. Neural categorization of this sort exists throughout the brain, up through the highest level of categories that we can be aware of. When we see trees, we see them as trees, not just as individual objects distinct from one another. The same with rocks, houses, windows, doors, and so on.
Since we are neural beings, our categories are formed through our embodiment. What that means is that the categories we form are part of our experience. What we call concepts are neural structures that allow us to mentally characterize our categories and reason about them.
What could be simpler or more obvious than color concepts? The sky is blue, fresh grass is green, blood is red, the sun and moon are yellow. We see color, and yet it is false, as false as another thing we see, the moving sun rising past the edge of the stationary earth.
Our experience of color is created by a combination of four factors: wavelengths of reflected light, lighting conditions, and two aspects of our bodies: (1) the three kinds of color cones in our retinas which absorb light of long, medium, and short wavelengths, and (2) the complex neural circuitry connected to those cones.
However, one physical property of the surface of an object matters for color: its reflectance, that is, the relative percentages of high-, medium-, and low-frequency light that it reflects. That is a constant. But the actual wavelengths of light reflected by an object are not a constant.
The wavelengths of light coming from an object depend on the nature of the light illuminating it: tungsten or fluorescent, daylight on a sunny or on a cloudy day, the light of dawn or dusk. Under different conditions, the wavelengths of light coming from an object will differ considerably, yet its color will be relatively constant, it will look pretty much the same. Color, then is not just the perception of wavelength; color constancy depends on the brain´s ability to compensate for variations in the light source.
Another crucial thing to bear in mind is that light is not colored. Visible light is electromagnetic radiation, like radio waves, vibrating within a certain frequency range, and only when such radiation impinges on our retinas are we able to see. We see a particular color when the surrounding conditions are right, when radiation in a certain range impinges on our retina and when our color cones absorb the radiation, producing an electric signal that is appropriately processed by the neural circuitry of our brains. The qualitative experience that this produces in us is what we call “color”.
Colors as we see them, say, the red of blood or the blue of the sky, are not out there in the blood or the sky. Indeed, the sky is not even an object. It has no surface for the color to be in. Without a physical surface, the sky does not have a surface reflectance to be detected as color. The sky is blue because the atmosphere transmits only a certain range of wavelengths of incoming light from the sun, and of the wavelengths it does transmit, it scatters some more than others. Thus, the sky is blue for a very different reason than a painting of the sky is blue. What we perceive as blue does not characterize a single “thing” in the world, neither “blueness” nor wavelength reflectance.
Color concepts are “interactional”; they arise from the interactions of our bodies, our brains, the reflective properties of objects, and electromagnetic radiation. Colors are not objective; there is in the grass or the sky no greenness or blueness independent of retinas, color cones, neural circuitry, and brains. Nor are colors purely subjective; they are neither a figment of our imaginations nor spontaneous creations of our brains.
Evolution has worked with physical limitations: only certain wavelengths of light get through the atmosphere, only certain chemicals react to short, medium, and long wavelengths, and so on. We have the color concepts we do because the physical limitations constraining evolution gave evolutionary advantages to beings with a color system that enabled them to function well in cucial aspects. We have evolved within these limitations to have the color systems we have, and they allow us to function well in the world.
