Illusions of Mind

Is it possible to maintain that we know other minds better than we know other bodies—or even our own body?  Can we be more skeptical about our knowledge of bodies than our knowledge of other minds? That sounds unlikely, given that we infer other minds from other bodies: we see other bodies and then conjecture what lies behind them mentally. We know external bodies better than we know external minds, don’t we? Isn’t that an axiom of epistemology? But there is a difference between the two sorts of knowledge that undermines this confidence: knowledge of other minds is not subject to visual illusion. There are no optical illusions of other people’s mental states, as there are no optical illusions of one’s own mental states. Our eyes never deceive us in this way. There are many optical illusions regarding physical objects, often quite striking: the visual brain is prone to these sorts of errors; there are glitches in the system. I needn’t give examples; they are a commonplace of psychology textbooks (the Muller-Lyer illusion will suffice to fix ideas). In addition, we have visual hallucinations in which whole scenes appear to us that don’t exist. You can’t believe your own eyes; they lie to your face. The visual system is inherently given to these illusions. The skeptic, then, can exploit them to undermine our knowledge of the external world—we might be under a giant sensory delusion. Perhaps my experience is not veridical but illusory; we can’t be certain this is not so, given the prevalence of illusion. It can even be argued that our impressions of color are visual illusions, since color does not really belong to objects. The visual system is set up for error, intrinsically fallible, a potent source of false belief. Knowledge based on it is shaky at best and non-existent at worst. It is an unreliable informant.

But the psychology textbooks record no examples of visual illusions of other minds. We don’t have visual impressions of other minds that mimic standard visual illusions: we don’t look at a bodily stimulus and seem to see a mental state that isn’t there. We may think a mental state is there that isn’t, but we don’t see such a state—we don’t have a visual experience as of a non-existent mental state. Our eyes don’t deceive us in this way. There is no Muller-Lyer illusion of the mind, or duck-rabbit drawing, or any other of the many illusions our eyes are prone to. Our perception doesn’t work this way. In fact, our perception of other minds is in this respect like our perception of our own mind: neither do we have illusions of non-existent mental states in ourselves. You never perceive a belief as a desire, say, or a belief that p as a belief that q, or an emotion as a thought. You are not capable of this kind of error: introspection is not prone to error through an analogue of optical illusion. There are no such glitches in the system; so, such error does not undermine claims to introspective knowledge. Skepticism cannot gain a foothold from this source. But nor can it gain a foothold from such a source in the case of knowledge of other minds. There is thus no argument from illusion in the case of knowledge of other minds: we never have a visual impression as of a non-existent mental state in someone else that is qualitatively just like a veridical visual impression of a real mental state—because we have no such visual impression to start with. We don’t seem to see a mental state as we can seem to see a physical state. You might see a body in an illusory way if (say) it had a Muller-Lyer figure etched on it, but you don’t (can’t) see a mind in such an illusory fashion; you can’t say “It really looked to me exactly as if he believes the sky is green, but I know he doesn’t actually believe that”. You don’t and can’t hallucinate another mind—as it might be a zombie that strikes you visually as replete with consciousness. You might believe a zombie has a mind, but you don’t see it that way: for what would a visual impression of a mind be like? There are no optical illusions of the mind, as there are no optical illusions of number (seeing 2 as 3, say). Your knowledge of other minds cannot therefore be undermined by their possibility or frequency; skepticism cannot be advanced on this basis. So, in this respect, knowledge of other minds is better off than knowledge of other bodies. I know your mind better than I know your body (or my own), as a matter of principle.

Does this mean there is no sense in which you can see another mind? That doesn’t follow, given the elasticity of the concept of seeing. And it sounds perfectly reasonable to describe our knowledge of other minds in this way: I can see that you are upset or happy or confused. Seeing is not restricted to a certain subsystem of our visual sense—the subsystem that produces visual illusions. So, there is a type of seeing that is not prone to visual illusions. Knowledge of another mind can be seeing it (or involve this), only not the kind of basic seeing that is subject to optical illusion. The case is not like theoretical inference in which no one would say seeing is involved (atoms and the like). This, too, provides a bulwark against skepticism about other minds; now we have knowledge backed by seeing that is not vulnerable to perceptual illusion. Things are looking up for our knowledge of other minds; it seems better off than many kinds of human knowledge traditionally thought superior to it. Might it be one of our best types of knowledge? That is certainly a pleasant thought (“You really know me!”) and it is not far from phenomenological reality: for it really does seem that I am (sometimes) perfectly well aware of what is going on in your mind—I can know, for example, that you are enjoying yourself while playing tennis or boiling an egg. I can see that it is so, and I know that no visual illusion can be getting in the way. What more could you ask for as a situation conducive to knowledge?[1] It isn’t like being surrounded by constant optical illusions or actual blindness: I am in the (or a) seeing relation to your mind, and I don’t have to worry about any malfunctioning in my visual system producing illusions. I am home free, epistemically. I can be quite smug about my knowledge of your inner life, not racked with epistemic anxiety. For I am using an illusion-proof visual faculty–unimprovable. Not so for physical objects; here I must contend with the vagaries of error-prone vision, the perpetual possibility of illusion and hallucination. I erroneously see objects as colored. LSD does a number on my sense of sight. I can’t even see when two short lines are the same length. No wonder the skeptic can attack my knowledge of physical reality, but he doesn’t have this resource in the case of my knowledge of other minds. I can therefore relax about this knowledge, secure in the knowledge that I will not be caught out by a processing error in my visual system. Nice![2]

[1] I am not ruling out other sources of skepticism such as lack of logical entailment—they are another story. But I do think the argument from illusions is one of the most potent and influential sources of skeptical doubt about our knowledge of the external world.

[2] Perceptual constancies provide a good illustration of the asymmetry I am drawing attention to. The brain must do a lot of work to cancel the effects of different sized retinal images in the perception of objects at varying distances, using various cues without which visual illusion would set in. But no such problem afflicts the perception of other minds: we don’t nurse a tendency to see minds as different sizes depending on their distance from our eyes, as we do in the case of heads. Nothing in the visual system is tugging us in the direction of falsely assigning different sizes to minds according to their distance. One might think that the human visual system is always on the brink of delivering false perceptions when it comes to physical objects, but not so for other minds.

Mathematical Philosophy

In 1919 Bertrand Russell published a book titled Introduction to Mathematical Philosophy, written while he was in jail; but the title is somewhat misleading, because the book isn’t about doing philosophy mathematically but about the philosophy of mathematics. Still, Russell did do a fair amount of mathematical philosophy: the theory of descriptions, existence as a propositional function, mathematical constructions of the external world, etc. So did Frege, Wittgenstein, Carnap, Quine, Tarski, Montague, Kripke, Davidson, and others. It was a movement, a meta-philosophy. We might call it formal philosophy or symbolic logic philosophy or technical philosophy or scientific philosophy—as opposed to informal philosophy or phenomenological philosophy or commonsense philosophy or ordinary language philosophy or humanistic philosophy. Its model is mathematical science not vernacular literature—arithmetic not art. It aligns itself with the mathematical member of the two cultures. I think we can add that analytic philosophy is by nature mathematical in that it employs conceptual analysis, which is a breakdown of the whole into its parts, isolated and enumerated. Concepts are composites of added parts. Such analysis results in equations—e.g., knowledge = true justified belief; it seeks conceptual equations. It also employs rigorous deduction like mathematics, hence the emphasis on logic: syllogisms, axioms and theorems, formalized arguments with premises and conclusions, logical variables. Thus, we have today formal epistemology, formal politics, formal ethics, formal semantics. The subject is steeped in formal methods and conceits. Twentieth century philosophy was awash in mathematics, for good or ill. The dispute between analytical philosophy and so-called continental philosophy might well be seen as a disagreement about the role of mathematical methods in philosophy—what do you prefer, aesthetics or arithmetic?

But I think this story has history skewed: philosophy has been mathematical for much longer—indeed, it has never really been non-mathematical. I think philosophy is, and always at heart has been, a mathematical science, more or less successfully. That is what it aspires to be, though we must be liberal about the meaning of “mathematical” and “science”. It is about abstract and abstruse questions, aiming for precision and exactitude, obsessed with number, methodologically a priori, in love with logic, proudly technical and symbolic. It is a kind of geometry or geography of concepts or facts or realities. One of its most fundamental questions is numerical: is the world One or Many—and if many, how many? Hence, monism, dualism, and pluralism. Is the world finite or infinite, continuous or discrete, qualitative or quantitative? What kind of mathematics best captures its nature? Philosophy is all about distinctions, divisions, differences, relations. Identity is always a central concept. For example, Plato’s problem of the one universal and the many particulars: this is a quintessentially philosophical problem, and it is overtly numerical. We have the abstract form and the concrete particulars instantiating it: the form is a unity, but the particulars are a plurality. These are essentially different kinds of entity, yet they are intimately connected: many things are white, say. How can the One be Many, and how can Many be One? What is the relationship between them? It seems puzzling. More generally, is the whole world a unity or is it a plurality? How many types of entity are there? Is a person two things in one (mind plus body)? Are there values and facts or just facts? Is appearance the same as reality? How many kinds of good are there?  Are pleasures all of one kind? How many types of truth are there? Is necessity unitary? Are all words names? Polytheism or monism?  And so on. We want to know how many; we want to count our ontological commitments. We want to mathematically analyze the world. There are odd numbers and even numbers—are there universals and particulars, minds and bodies, values and facts? We look for unity but accept multiplicity. In arithmetic it all comes down to addition (subtraction is just the opposite of addition)—is that the way it is with the world generally? Metaphysics is a kind of mathematics of reality in its broadest outlines. We are applying mathematical conceptions, albeit elementary ones (but are any mathematical conceptions truly elementary?). This is not all we are doing, to be sure, but it is a large part of it; we are employing a diverse range of knowledge in conjunction with our mathematical knowledge.

So, the mathematical paradigm did not suddenly emerge in the twentieth century; it was alive and well for two thousand years or more. But it is so natural to us that we don’t notice it; we mathematize instinctively. Philosophy could hardly exist without it—or any science. It’s how we think scientifically, rigorously, systematically. The only question is how much we insist on it or extend it. I am not myself enamored of a sharp distinction between science and literature (I think literature is a type of science, mainly psychological). I think the human mind is essentially mathematical, here as elsewhere. It’s just a matter of admitting it, making it explicit as part of one’s meta-philosophy. We don’t have to mathematize philosophy because it is already mathematical. Even Sartre’s existentialism is mathematical, because it insists on the duality of the in-itself and the for-itself: Sartre is an ontological dualist—two things not one. The philosophy of language as it now exists is clearly a branch of mathematics—what with model theory and computational linguistics. Mathematical thinking is so entrenched in philosophy that we risk accusations of triviality just by drawing attention to it. It is an interesting question in the pre-history of ideas whether philosophy evolved in the human mind as an offshoot of an antecedent mathematical faculty. We are natural accountants, calculators, and bean counters; we brought these talents to bear on the most general questions of the cosmos. Mathematicians often have philosophical predilections. Mathematics and philosophy belong to the same intellectual natural kind.[1]

[1] Pretty much all science is mathematical to one degree or another; it would be strange if philosophical science were the exception. Inside each philosopher is a little mathematician struggling to strut his stuff.