Are there non-physical properties of experience that cannot be explained by physical facts? One thought experiment sought to explore this very question.
Let’s imagine the following scenario: a scientist named Mary is trapped in a cell. She’s been trapped in this cell her entire life and the cell is entirely black and white. No colour enters into her field of vision. And yet, Mary is a brilliant scientist who knows everything about the science of vision and how light interacts with biological and non-biological matter. She understands how electromagnetic radiation interacts with the cones and rods in our eyes. If Mary were to venture out of this uncoloured room into a world of colour, what would she see? Would Mary learn anything new upon seeing an apple?
This thought experiment, known as “The Knowledge Argument,” was proposed by the philosopher Frank Jackson to suggest that there are certain “facts” about existence that are not physical. This thought experiment was originally issued as a challenge to physicalism, the idea that all that exists is physical. The idea here is that conscious experience is itself a source of knowledge. These (supposedly) non-physical properties of experience are called qualia. Qualia such as the colour green, the taste of sugar, Middle C, etc. are unique to whoever experiences them.
So what is the answer to this thought experiment? Are there non-physical properties of experience that cannot be explained by physical facts?
Our first step is to re-imagine the thought experiment with respect to sound. This is simply for the purposes of better intuition and you’ll eventually see why. Here we have Mary as an erudite audiologist who has all the physical facts about the ear and the vibration of pressure waves in the air. Mary, however, has never heard a sound. She is not deaf but she has not been exposed to soundwaves. She lives in a soundproof cell and cannot even hear herself sneeze. What happens when she hears a vibrating A440 tuning fork upon leaving the soundproof cell?
It’s very likely as an audiologist — or some other kind of sensory neuroscientist — Mary would be familiar with the idea of stimulus modalities. Stimulus modalities are the ways we describe environmental stimuli that manifest themselves to us. For humans, the corresponding stimulus modality for electromagnetic radiation is colour; for pressure waves, it’s sound; for the chemical reaction of gustatory receptor cells and food, it’s taste, etc.
So continuing with sound, the issue remains: would Mary know what it’s like to hear an A4 sine wave? What is A4? A4 is the label that we give to the audible oscillation of pressure waves at a frequency of 440 Hz. The problem with this argument comes from the following question: what does it sound like?
This is where I take issue with the Knowledge Argument. The A4 sine tone does not “sound” like anything. We just said qualia are unique to the person experiencing them. They are definitionally subjective. Yet, the question of what A4 “sounds like” is an attempt to objectify A4.
Additionally, this becomes even more complicated since there are different tonal music systems. Some tonal music systems don’t signify 261.6 Hz and thus don’t have a concept of Middle C. The Knowledge Argument assumes that the norms for classifying perceptual stimuli are universal. They’re not. The same principle can be applied to the original formulation of Mary’s Room. Would she know the names of colours? In the first formulation, I asked about her interaction with an apple upon leaving her cell. Would she know that the colour of the apple is red and not green, or yellow?
The fundamental issue is that there is no fact of the matter as to what it is like to see ‘red’. This is to say, there is no fact of the matter as to how electromagnetic radiation — with a wavelength of λ=0.633 μm — is processed by the human eye. The colour red, Middle C, and other qualia must be properly understood as processes like digestion and photosynthesis.
Take plants, for example. Do they experience colour? In photosystem II, the first step of the photosynthetic process, chlorophyll a (P680), absorbs light with a wavelength of λ=680 nm. In the second step, photosystem I, chlorophyll b (P700) absorbs light of wavelength λ=700 nm. These are general descriptions of the photosynthetic process, but these processes are different for each plant cell. But when it comes to an analysis of the process, who’s to say that one cell’s photosynthetic process is more correct than that of another cell? When all is said and done, we just have vocabularies to facilitate distinguishing between different percepts. This process extends not only to plants, but to other animals. There are animals that can detect percepts that we cannot detect. Bats and dolphins have echolocation and they likely have their own methods of classifying these percepts, a sort of “proto-vocabulary” for perceptual organization.
The way you experience a particular stimulus is a product of the psychological context you bring to that experience. Some cultures don’t make the distinction between blue and green because of their language. Some cultures have different foods and will therefore taste a cheeseburger very differently than a typical American would.
“The way you experience a particular stimulus is a product of the psychological context you bring to that experience. Some cultures don’t make the distinction between blue and green because of their language.”
In an interview on Closer to Truth, the following exchange took place between Robert Lawrence Kuhn and the late artificial intelligence researcher Marvin Minsky:
Kuhn: I don’t know if the blue I see looks the same to the blue you see even though we both call it blue because this first-person subjective experience and the fact that there is a first-person subjective experience means that consciousness is something special.
Minsky: Well, the first answer is that what you see as blue is not what I see as blue because I have different mental processes so they’re making some kind of assumption that’s just plain silly.
Minsky’s argument is that our perceptual intuitions are inherently relative. But additionally, even within a normative structure the meaning is necessarily external not internal; this is related to the inverted spectrum argument. Qualia cannot be divorced from a perspective even in principle. The label is arbitrary and contextual, not intrinsic in the sensation.
The Knowledge Argument has since been abandoned by its founder. Jackson’s current view is that seeing a red apple would still correspond to some physical event taking place in Mary’s brain. However, this physical event is nevertheless different for each person’s brain. The flaw in Jackson’s argument is that it takes a set of norms for granted. Our qualia only belong to us on an individual level. The consistency is only in the application of the vocabularies we use to describe them. If we can’t even pin down the percept itself and isolate it for examination, how can we expect to extrapolate it across entire populations and cultures?
What is objective…is what is subject to laws, what can be conceived and judged, what is expressible in words. What is purely intuitable is not communicable.
Often, therefore, a colour word does not signify our subjective sensation, which we cannot know to agree with anyone else’s (for obviously calling things by the same name does not guarantee as much), but rather an objective quality.
— Gottlob Frege, Die Grundlagen der Arithmetik (The Foundations of Arithmetic), (Section 26)
Emeka Ikpeazu is a recent graduate in Electrical Engineering from the University of Virginia. In his spare time he likes to write, go on long runs, watch movies, and listen to classical and jazz music.