Consciousness and the Eye

 

 

If you look into the eye of an animal (say, a bird) you gain a strong impression of consciousness: the eye seems to brim with consciousness. The same is not true of other sense organs: you don’t get a comparable impression from looking at the ears or nose or skin. This suggests that there is particularly close connection between vision and consciousness—vision is par excellence an exemplar of consciousness. The eye is a receptor that responds to light, a transducer that converts an impinging light stimulus into nervous activity, and ultimately into a conscious impression of the world. Thus there is a close connection between light and consciousness. Elsewhere I have suggested that light is the reason that consciousness exists on planet Earth: because of light from the Sun evolution designed an organ that could respond consciously to this rich source of information, and no other stimulus could trigger such a radical biological innovation.  [1] I call this the “optical theory of consciousness”. The optical theory says, crudely, that light causes consciousness; less crudely, that light-sensitive tissue is the kind that uniquely gives rise to consciousness. No light, no consciousness; with light, consciousness predictably develops. I will make some further remarks in defense of this theory, particularly with respect to the uniqueness claim.

            Light has some claim to be the most remarkable physical phenomenon in the universe (in some sense of “remarkable”). The eye has some claim to be the most remarkable biological adaptation, and consciousness the most remarkable psychological phenomenon. Clearly, there must be a reason that the properties of light lead so reliably to the existence of eyes (the convergent evolution of eyes is well known): there is something about light that makes it worth responding to—and worth being conscious of. It is a stimulus that craves a response—that demands to be recognized. You would be a fool to take no notice of light, biologically speaking. Hence animals that live in light tend to be sensitive to it; and there are eyes everywhere, beady and acute. But what exactly is so special about light? We know its speed is special, being both constant and maximal. That sets it apart from everything else—the character of its motion. But it is hard to see how this property of light would be biologically significant: even if light were slower or its velocity variable, it would still be the stimulus that it is from the organism’s point of view. Light also travels in a vacuum, divides into a spectrum of wavelengths, has particle-wave duality, and has zero mass—but again, these properties have little to do with light as a biological stimulus. The feature of light that is most relevant to its stimulus profile is surely its informational density: there is just so much information present in the light that impinges on the typical retina. This is because of its physical structure—all the billions of photons reflected off surfaces bearing fine-grained information about those surfaces. This is a powerful resource for organisms to tap into—a detailed map of what is going on around the organism. The claim of the optical theory is that consciousness arises when a threshold of informational complexity is reached, but not before, and that light alone reaches that threshold. I won’t repeat the arguments for this view now, but I do want to address some potential objections that cry out for answers.

            The most obvious objection is that vision is not the only conscious sense. How then could light uniquelycause consciousness to evolve? Don’t sound and physical contact also cause hearing and touch to evolve? Aren’t these also associated with states of consciousness? The optical theory must reply that consciousness originallyarose in connection with eyes and only subsequently spread to the other senses. That may sound ad hoc, but actually it is not so far-fetched. It is quite commonplace for an adaptation to arise in a certain way and then become repurposed for other functions—as when feathers arose for thermal regulation and then were co-opted for flight. Maybe consciousness came with eyes alone but then the other senses recruited it as an enrichment—before that they operated without consciousness. Given that there can be subconscious perception, this is perfectly possible. Similarly, other properties common to the senses might have arisen originally in connection with vision, but were then distributed more broadly: that might be true of perceptual segmentation or perceptual computation or perceptual constancy. Segmentation is useful in visual perception and it may have started life in that domain—indeed, it may not have been possible in a different domain as an initial adaptation. We have trait transfer following trait origination. Evidence for this would be telltale remnants of the origin of the trait—say, visual-auditory synesthesia. Maybe such synesthesia was more common soon after hearing borrowed consciousness from vision, later phased out as pointless. Or there might be abstract structural features of visual consciousness that show up in auditory consciousness, bearing witness to their origins (“quality spaces”). Or there may be metaphors drawn from vision and applied to the other senses. So the objection is not as decisive as it may sound—the optical theory has potential resources with which to explain the spread of consciousness to non-visual senses. If we grant that the non-visual senses don’t command stimuli that inherently cross the threshold of informational density required to create consciousness, then the optical theory might be the only way to explain why they are nevertheless accompanied by consciousness.

            A sharper test of the optical theory is supplied by the physiology of actual animals on Earth. The theory would be decisively refuted by the existence of two sorts of animal: those with eyes but no consciousness, and those with consciousness but no eyes. Such animals would show that eyes are neither sufficient nor necessary for consciousness—seeing automata and blind sentience. A survey of the animal kingdom fails to turn up any animals of the former kind: no animals both have eyes and are clearly not conscious. You might point to the compound eyes of insects, but (a) it is not clear that insects are devoid of consciousness and (b) we could always restrict the optical theory to more sophisticated eyes (such as the camera-like variety). It is a striking fact how well correlated eyes and sentience are—we don’t find animals with developed eyes going around like zombies! In fact, the animals with the best eyes always seem particularly alert and conscious—birds, for example. In contrast, the dull and sluggish eye tends to be correlated with manifest somnolence, a drowsy mode of being. But the second kind of animal is more challenging for the theory: what about animals that see nothing but feel at lot? We talk about being “as blind as a bat”, but we don’t hesitate to call bats conscious. Why can’t there be an animal with acutely conscious hearing but no seeing eyes? Isn’t that the case for the human blind?

            The answer to this worry is that the optical theory does not claim (absurdly) that consciousness is only possible in the sighted; it claims that consciousness arises in evolution specifically from the visual sense. So it is entirely possible for sight to be reduced or eliminated in a species as a result of changing environmental conditions, despite the fact that it arose in a visual setting. A genuine counterexample would have to be an animal with no sighted ancestors that is nevertheless fully conscious. Bats have vision and may well have evolved from animals with better vision (not being nocturnal), so their consciousness could easily have arisen from vision, and only from vision. Similarly for blind snakes and moles: their evolutionary history might well have included sighted ancestors. I don’t know of any animals that are clearly conscious but have nothing visual in their present make-up or evolutionary history; so vision could be the sole source of the brain structures that make for consciousness. Those brain structures may persist in a biological line while eyes themselves are phased out. There are certainly organisms that have blindness written deep in their genes—such as bacteria, viruses, plants, plankton, jellyfish, and eyeless worms—but they are all strong candidates for zombie status. The correlation between consciousness and eyes is strong, and not coincidental according to the optical theory. It is also strong between other sense organs and consciousness, but the optical theory claims that consciousness arises (originally) only in the context of stimuli that reach a certain threshold of informational density, which light alone reaches.

The kind of density found in a typical visual experience is never matched by the density found in an auditory experience—simply because packets of light are physically much richer than sound waves. The stimulus causing your eardrum to vibrate has nothing like the complexity of the stimulus falling on your retina, and similarly for tactile and olfactory stimuli. The brain will process a stimulus unconsciously if it can (consciousness being biologically costly); it will only invoke consciousness if the stimulus is so complex as not to be susceptible to unconscious analysis. Natural selection has apparently decided that the costs of consciousness are worth it in order to extract encyclopedias of information from the visual stimulus. If the planet were perpetually dark, there would be no need for consciousness: eyes would be pointless and the other sorts of physical stimulus don’t call for anything beyond unconscious processing. Imagine that those stimuli were even more impoverished than they are now, with precious little information contained in them: the atmosphere might be thin and unresponsive, so that sound waves possess little structure or energy; or the chemicals emitted by objects might reach the nostrils in small numbers. A relatively simple sensory mechanism will suffice for maximum information extraction from these limited stimuli; there is no need for the elaborate and metabolically expensive machinery of sensory consciousness. Well, compared to light stimuli, actual-world non-visual stimuli are similarly impoverished—as a matter of the simple physics of the stimuli.

Let me drive the point home by distinguishing synchronic and diachronic informational density. We have not only the photons currently striking the retina; we also have the photons striking it a moment later, updating the perceiver’s image of the surrounding world. This happens with inconceivable rapidity as battalions of photons continuously bombard the retina; the information conveyed concerning changes in the environment is virtually incalculable (just think of catching a ball). This is a colossal task of perceptual analysis, orders of magnitude beyond what can be achieved with the ears (not that this is unimpressive). Echolocation is remarkable, but it is not to be compared to vision, which is presumably why so few animals substitute the one for the other. The auditory stimulus is simply not rich enough, no matter how adept the animal may be at echo detection. Sounds are mediated by perturbations of molecules in the atmosphere, a fairly crude way to transfer information, but light has limitless bandwidth and extreme fineness of structure. The retina has to absorb what this stimulus imparts, then have it instantly replaced by a new stimulus, keeping track of the changes. The optical theory says that it is this challenge that brings sensory consciousness into existence. We don’t know how this happens, or even why it needs to happen, but evidently that is the way things work. It just seems to be a natural fact about light and consciousness that the former triggers the latter (given the right evolutionary context). If we subscribe to panpsychism, we could say that the consciousness-creating properties of matter would remain latent if it were not for vision.  [2] The other senses don’t need to go beyond the non-conscious aspects of matter to perform their work, but vision needs more advanced machinery to perform its work (why, we don’t know). If the world were completely dark, the psychic properties would not coalesce into conscious experience, but light operates to elicit them to produce such experience. However consciousness may be generated, the optical theory says that light-sensitivity is the original trigger that causes it to emerge. We know that light provides the energy that drives the entire biological world (via photosynthesis) but it also turns out that it drives the emergence of consciousness in the psychological world (what we might call “photo-sentience”).

If the optical theory is on the right lines, a good place to look to gain understanding of consciousness would be the psychophysics of light. This has been extensively studied, particularly with respect to receptor cells in the retina (rods and cones etc). But a more self-conscious study of light as it relates to consciousness might prove helpful: particularly the kind of internal structure both have. Is it a granular or a continuous structure, or possibly a mixture of both? Light seems to have both sorts of structure depending on the context (behaving sometimes like a wave, sometimes like a particle), and there is some reason to find the same sort of duality in visual consciousness. If consciousness evolved as an adaptive response to light, it might inherit some of the features of light, structurally if not in substance (consciousness is surely not made of light). Response mirrors stimulus; effect reflects cause. At least this looks like an interesting research program. The nature of the biological world is shaped by the fact that photosynthesis lies at the root of everything organic, so it is reasonable to expect that the psychological world would reflect the centrality of light in shaping the mind. Light is the aspect of the environment that has exercised the most profound influence on the nature of sensory experience (according to the optical theory). Consciousness is the progeny of light—what happens to organisms when light-sensitive receptors come into the world.

No doubt the optical theory is highly speculative, also counterintuitive in some respects, but it provides a novel way to think about a problem sorely in need of fresh avenues of inquiry. It also has a poetically attractive quality: light and consciousness turn out to be made for each other, in virtue of the brute physics of light. There is nothing in the universe quite like light, and there is nothing in the universe quite like consciousness: these two remarkable things turn out to be deeply connected.

 

Colin McGinn         

           

  [1] See “Consciousness and Light”, in Philosophical Provocations: 55 Essays (MIT Press, 2017). I will not here repeat the arguments for this position.

  [2] I put it this way for expository purposes not because I subscribe to panpsychism. I also hope it is clear that the optical theory is in no way incompatible with the idea that consciousness is mysterious, quite the contrary.

                                   

 

 

 

Matter and the Limits of Skepticism

 

 

The skeptic questions whether we know the external world exists, purporting to provide a proof that we don’t know that it does. The proof takes the form of describing a possible alternative to what we normally assume. Thus it is suggested that a deceiving demon is a possibility, or that we might be dreaming, or that we might be a brain in a vat. Since these are real logical possibilities that we can’t rule out, we must conclude that we don’t know that the world is as we normally take it to be. For instance, I don’t now know that I am sitting at a desk looking at a tree. It might all be one vast illusion or hallucination. It is important to this argument that the skeptical alternative be a real possibility, which must be accepted as such, or else we could simply reply that no such thing is possible, so there is nothing we need to rule out in order to know what we think we know. If the skeptic suggests something impossible, or not clearly possible, his argument is toothless; and the usual suggestions satisfy this condition, since they do describe real logical possibilities, often rooted in familiar facts (people can and do deceive us, we do dream, and we do suffer illusions and hallucinations).

            But what about our belief that matter exists? This is not the belief that the external world exists as we customarily think of it, but just the belief that matter of some sort exists. If I am a brain in a vat, then what I take to be the external world is all illusion, but matter still exists in the form of vats and brains. If I am in bed dreaming, then my material bed and body exist even if what I dream about doesn’t. The evil demon can be as material as you like and still deceive me. So the question of matter is very different from the question of the external world as normally conceived. Is it possible to be a skeptic about the existence of matter? Can the skeptic show that we don’t know that matter exists? Can he give a proof of this analogous to his proof that we don’t know the external world exists? Clearly he can’t do this by suggesting his usual logical possibilities, since these all presuppose the existence of matter, so they are not alternatives in which there is no matter. He needs a real possible world in which mind exists but there is no matter of any kind, in order to provide such a proof. He needs to provide a logical possibility that we can’t rule out.

            This is a much more difficult thing to do than the usual exercises in skepticism, because there is nothing familiar he can rely on—no actual cases in which we have mind without matter (as there are actual cases of sense impressions without external objects of perception). What has to be claimed is that it is possible to have disembodied minds in a wholly non-material world. And the problem is that this is not clearly possible and may well be quite impossible, so the skeptic has not discharged his obligation to produce a genuinely possible alternative to what we normally take for granted. We do not therefore need to listen to his argument; he has no argument against our belief that our minds exist in a world of matter. Nothing he has to say proves that we don’t know what we take ourselves to know. So this belief about the world beyond the mind is not vulnerable to skeptical challenge of the standard (distressingly convincing) kind.

            To clarify the point, let’s consider two other types of skepticism regarding the non-mental world, concerning time and space. Suppose the skeptic says that we don’t know that time exists: we have impressions of time, but there may be no objective time corresponding to these impressions. This, he contends, is a real possibility—that minds can exist without time existing. We would be within our rights to reply that this is not a real possibility: minds exist in time and must do so. For minds change and change requires time—our consciousness consists of temporally successive states. So the skeptic has not provided an indisputable logical possibility that is an alternative to the way we normally takes things to be; at best he has suggested a highly questionable metaphysical theory, namely that minds can exist without time existing. He has certainly not proved that this is a possibility. So he has not undermined our claim to know that time exists by pointing to a logically possible alternative in which we have the same impressions of time but there is no time.

Now consider space: the skeptic claims again that we don’t know that space exists, despite our impressions of space. The reason is that it is logically possible for minds to exist without space, and we can’t rule out the possibility that our minds are like that. But again, we can reply that it is not logically possible to have minds without space—minds necessarily exist in a world of space. Certainly the skeptic has not proved that his supposed alternative is logically possible.  [1] We might argue against him that minds cannot be individuated without space, since space provides the indispensable basis for establishing the numerical distinctness of minds—your mind is not identical to my mind because our minds are in different places. The skeptic might engage in a metaphysical argument with us about this, but he has certainly not suggested an indisputable possibility that we are obliged to accept. So we are not in the same epistemic predicament with respect to our belief in space that we are in with respect to our belief in the external world (as distinct from the world of matter). We are not vulnerable to skeptical doubt in the same way, viz. by exhibiting a clear logical possibility that our evidence fails to rule out.

            Similarly with respect to matter: if the skeptic says that there could be minds without matter, we can reply that we don’t agree with that, since minds require brains. These brains may not be as we normally conceive of them, but there has to be some material basis for minds—they cannot be purely immaterial. The skeptic may engage us in metaphysical argument at this point, but what he can’t do is point out that we ourselves accept his alleged possibility as a real possibility—as we do for the brain in a vat possibility. Whether we can prove that mind requires matter is not to the point; the question is whether he can prove that minds can exist without matter. For that is the possibility he needs if he is to show that we don’t know that matter exists. He needs a certain metaphysical possibility to undermine our confidence in what we ordinarily believe, but it is not clear that he has one—or rather, it is clear that he does not have one. So there is a significant asymmetry between this type of belief and the type of belief the usual skeptic questions. The usual skepticism does not then generalize to these further beliefs—in time, space, and matter. Our claim to know of the existence of these things has not been undermined, even granted that our claim to know the existence and nature of the external world has been undermined.  [2]

            It may be thought that this is a disappointing result, since we have made no inroads against the skeptic on his favorite territory: for all I have said, we still don’t know we are not dreaming, not a brain in a vat, and not the victim of a deceiving demon. But this is too pessimistic (or perhaps I should say too optimistic) because we have established a definite limit to the corrosive power of skepticism: there are beliefs about the non-mental world that are immune to skeptical challenge (at least of the usual kind). For all that the skeptic has said, we do have knowledge concerning the world beyond the mind—he has said nothing to undermine our confident belief in objective time, space, and matter. His skepticism is thus confined to a certain subset of beliefs about objective reality. I count this a strong anti-skeptical result, even if it falls short of what we might ideally hope for.

 

  [1] The skeptic can point out that we know of cases in which a sense impression has no corresponding object and then ask how we know this is not always the case, but he cannot likewise point to cases of minds without time, space, and matter and ask how we know our minds are not in this position. There are no such actual cases to point to. 

  [2] That is, our belief that we sense external objects and are not subject to massive illusion: this belief isundermined by the skeptic. But he has not undermined our more general belief in things outside the mind. 

                                                Intention and Possibility

 

 

How does the idea of possibility enter our thought? It is generally agreed that perception is not its source: we do not see possibility—we don’t think of possibility because our senses present it to us. A more likely view is that imagination is the progenitor of the idea of possibility: it is because we imagine that the idea of possibility occurs to us. What is imaginable is possible and what is unimaginable is impossible. We find ourselves imagining things and therewith we introduce the idea of what could be. More strongly, we could not come up with the idea of possibility in any other way—imagination is our only access to the realm of the possible. Perception is certainly not, and what else is there? This theory has the result that a creature without imagination would be modally blind: it would have no use for the concept of possibility and no means of acquiring that concept. If the concept of the possible simply is the concept of the imaginable, then we cannot have the former without having the latter; but even if the connection is weaker, imagination is essential for the recognition of possibility.   

            The view is not without difficulties. Can we not imagine the impossible (water without H2O, disembodied minds)? And aren’t there possibilities that we can’t imagine simply because of our imaginative limitations (four-dimensional space, infinite time)? But I won’t discuss these well-worn issues; instead I will propose an alternative theory that I think has some merits. This alternative allows possibility to enter thought without benefit of the imagination, so that modal thinking can exist in the absence of imagination; the concept belongs in another matrix of interconnected concepts. The central concept in this matrix is intention: the concept of possibility is bound up with the concept of intention. This is because we can intend only what we believe or know is possible. If I believe it to be impossible to jump to the moon, then I cannot intend to jump to the moon. I can intend to do what I believe to be improbable, but not what I believe to be impossible. This is clearly true for logical or metaphysical impossibility, but it applies also to nomological impossibility: I cannot intend to do what I know to violate the laws of nature (as with jumping to the moon).

Thus when forming an intention I must be cognizant of possibility, implicitly or explicitly. This is a conceptual truth: it is conceptually impossible knowingly to intend the impossible. Accordingly, I cannot intend to intend what I know to be impossible, since that is itself impossible. To have the concept of intention is to know that intentions must concern the possible. If someone orders you to perform the impossible, you can rightly reply that you cannot form any such intention. You cannot be punished for failing to intend to do what you know it is impossible to do. This is simply beyond the power of your will. Thus the concept of intention embeds the provision that while you can intend a great many things you cannot intend what you know to be impossible. To have intentions is to be aware of this fact, and hence to have a grasp of the concept of possibility. It is not so for desire: you can desire what you know to be impossible, because desire does not have to reckon with the facts of the world. But intention is the intention to act and action perforce takes place in the world of possibility—hence you have to believe that your actions could realize your intentions. Even a cat gauging a difficult jump has to consider the possibility of success, and if it judges that success is impossible it will neither jump nor intend to. For reflective humans, understanding the nature of intention brings with it a grasp of possibility and impossibility. Thus we naturally contemplate possibility when we form intentions; we may even reason about possibility when deciding what to do.

But what should we say about more abstract and theoretical ideas of logical and metaphysical possibility? Here we can deploy the idea of a superior agent: logical impossibility is what God cannot intend to bring about. Even God could not intend to square the circle: his will is limited by his knowledge of modality. It isn’t that he can’t imagine doing this; it’s that he can’t intend to do it. And he knows he can’t intend it, whatever may be the case for his knowledge of what he can imagine. The impossible is that which cannot be intended—even by God. The concept of possibility is inextricably linked to the concept of intention, because intentions are modally sensitive—they must track what is possible and impossible.

The nice thing about this theory is that it locates modal concepts in something basic and practical. These concepts do not have to be seen as transcending the empirical world, as objects of pure intellectual apprehension; they arise from basic facts about agency.  [1] We think this way because we are agents with intentions, and intentions must respect possibility. Any intention-forming agent must be sensitive to the modal facts: the limits of intention are the limits of the possible. The concept of the possible is the concept of what can conceivably be intended, while the concept of the impossible is the concept of what cannot conceivably be intended.

 

Colin McGinn    

  [1] These basic facts include the concept of ability—what an agent is able to do. No agent can intend to do what he knows he is not able to do, for one reason or another. So modal concepts have their roots in the concept of ability, which can be extended to different types of agent with different types of ability, up to the case of God. They are not quite as unworldly as they can be made to sound. In a certain sense abstract metaphysics has its roots in practical action.

                                               

 

 

 

Language as a Tool for Thought

 

 

A typical tool must meet two requirements: it must be able to be used by its intended user, and it must perform its designated function. Often the tool must be firmly gripped and manipulated, so it must fit into the human hand, while its other end performs the task in question. If we think of spoken language as a tool for communication, we should expect the same duality: it must be both usable and effective. What this comes down to is that the words of the language must be pronounceable and audible. The speaker must be able to utter the words and the hearer must be able to hear them. These are nontrivial requirements, familiar as they are: words could be pronounceable yet inaudible (mere whispers) or they could be audible yet not pronounceable (not conform to the human vocal system). Spoken human languages, as we find them, combine these two characteristics, so they are both usable and effective. True, words can be hard to pronounce and fatigue can set in, and ambient sounds can drown utterances out; but generally words meet the two necessary conditions of a successful communicative tool. We can imagine situations in which they don’t, where nothing pronounceable is audible and vice versa (a noisy planet and inept voices). Then there would be no such thing as a spoken language–or a sign language, if visual conditions were not conducive (perpetual thick fog).

            But what about language as a tool of thought—what design features would we expect to find built into language that performed this function? It would need to be mentally manipulated and it would have to serve the purposes of thought. Thus it would need to consist of storable, segmented, manageable words that combine to produce complex novel constructions. It’s no use if the complex constructions consist of parts that the mind can’t handle (the analogue of words that can’t be pronounced), or if the parts can be easily handled but can’t form complex constructions like sentences. But natural languages meet the two requirements for being a cognitive tool quite neatly: the human mind can store, process, and manipulate words; and words can combine into phrases and sentences that can express an infinitude of thoughts. The basic architecture of natural languages thus suits them to be tools of thought, since they can be both used by the thinker and also serve the purpose of thinking, viz. encoding complex novel thoughts. The lexicon plus the grammar can be mentally manipulated, and the products of this manipulation serve to encode thoughts, which can enter into reasoning, practical and theoretical, which can lead to action. Without this finely wrought tool thought would not be as effective as it is (it might not exist at all in anything like its present form), and luckily an effective tool exists that can also be handled by the thinking mind. If words could not exist in internalized form, then language could not perform the cognitive function it now performs—at best we would have to speak out loud whenever we entertained a thought. Words and syntax can exist both internally and externally, and because of this language can serve as both a tool of communication and a tool of thought.

I am stating truisms. I have simply set the basic property of language in the context of the notion of a tool—language as a finite stock of discrete digital elements that can be combined by syntactic rules into an infinite array of structured hierarchically organized complex expressions. I have said that this formal object satisfies the two conditions on being a tool of thought: it is both mentally accessible and functionally effective. If it were not finitely based, it might still serve the purposes of thought as a potentially infinite system, but it would not be accessible to finite minds such as ours–while if it could not express a potential infinity of thoughts, its mental accessibility would not help in performing the task at hand. Many animals have access to symbolic systems of some kind (bees, whales), but these systems do not permit the kind of recursive unbounded scope we find in human languages. And the gods might speak languages matching or exceeding ours in expressive power, but are beyond our capacity to master (perhaps because of memory limitations). The design features of a tool are suspended between the two requirements, reflecting those requirements, and are sometimes compromises between them. They are best understood as the joint result of limited human capacities and a desired objective—possibly being a trade-off between the two. There is no point in designing a perfect tool that can’t be used, and usable tools can be effective enough without being perfect.

With these preliminary points in mind, then, I wish to make my main positive proposal: human languages make effective tools of thought (partly) because they permit the formation of conceptual distinctions. Words enable us to formulate distinctions that would not be possible without them—not possible given our contingent psychological nature. They may not be ideal tools for this job—no tool is ideal for any job—but they perform it well enough, and it is hard to see what might perform it better. One central goal of thought is the making of fine distinctions (in addition to producing new thoughts) and language is inherently suited to facilitating this process. Lest I be accused of further truism, let me state the thesis more forthrightly: the distinctions that exist between words as such are used as a tool to construct distinctions of meaning, i.e. conceptual distinctions. The mind invokes words qua formal objects to aid it in the process of conceptual distinction making. This is the analogue of the thesis that the mind uses the combinatorial power of language to aid it in combining concepts into thoughts—it recruits syntax as a device of thought assembly. Similarly, the mind uses lexical distinctness as a tool for generating conceptual distinctness. Note that this is not the thesis that conceptual distinctness is lexical distinctness but rather the thesis that lexical distinctness is used as a tool for constructing conceptual distinctness. A hammer is a tool for knocking nails in not a nail that has been knocked in; a language is (inter alia) a tool for making conceptual distinctions not a conceptual distinction itself. It is not just that human language permits an infinite number of thoughts; it also permits an infinite number of finely individuated thoughts. A language is a thought-slicer, a concept-differentiator. It is designed to generate ever finer conceptual distinctions, and it does so by containing fine distinctions itself.  [1]

There are many kinds of conceptual distinction; I shall mention three. First, we have distinct but co-extensive concepts, expressed by co-denoting names and co-extensive predicates. We have separate words for these concepts (“Hesperus” and “Phosphorus”, “creature with a heart”, “creature with a kidney”). There might possibly be a language that failed to provide for such conceptual distinctions—that was completely extensional in meaning: but no human language is like that. It would surely be impoverished relative to ours, if more to the liking of certain logicians. Second, we have near-synonymy—words that are close in meaning but not really synonyms: “house” and “home”, “friend” and “ally”, “stone” and “rock”. These are important because they illustrate the pervasiveness of distinction making: the concepts may be very similar but they are not exactly the same; there is a conceptual distinction to be made. Third, we have straight synonymy—identity of concept expressed: “bachelor” and “unmarried male”—that type of thing. Even here different words are suitable in different contexts, so there are distinctions to be made. Human language is rich in synonyms, as well as near-synonyms and co-extensive non-synonyms: that is, it is rich in conceptual (semantic) distinctions. It seems to make a point of registering such distinctions, as if it matters. It insists on marking subtle differences of meaning. This is not throwaway redundancy, but attentiveness to fine distinctions of human thought. I venture to suggest that it is a universal feature of all human languages (though not all possible languages): they all contain the machinery for recording fine-spun distinctions, and also the machinery for making new fine-spun distinctions. In thought we are constantly recognizing and creating conceptual distinctions: the thesis is that human languages aid in that process, crucially so. Words are the knives of thought: they chop things up finely.

Chomsky talks about the Merge operation that combines words into collections of words, construed as a function from sets to sets.  [2] Clearly language requires such an operation, because it is combinatorial; and the mind must be able to compute Merge if it is to exploit the combinatorial power of language. Let me likewise introduce an operation I call Dissect that operates on concepts to generate more fine-grained concepts. Suppose we start with an undifferentiated concept people and then apply Dissect to this concept to derive the concepts men and women: we have gone from a concept treated as unitary to two concepts that distinguish among the members of the class consisting of people. If we applied Dissect to the set of people (not the concept people), it would partition that set into two subsets, viz. the set of men and the set of women—so it would be the opposite of Merge. If we apply it to concepts (or word-like elements in the language of thought), it generates two new concepts (or inner words)—thereby introducing a conceptual (semantic) distinction. I do not claim that I know how Dissect works (it seems rather mysterious), but evidently it does, since we make new distinctions all the time. We suddenly (or slowly) “see the difference between X and Y” and feel a sense of accomplishment or enlightenment. We implicitly grasped the distinction (whatever quite that means) and now we grasp it fully and consciously. Language enables us to make the leap: our language faculty feeds into our cognitive faculty and awakens us to distinctions that had been blurred or elusive before. Thus we employ Dissect in conjunction with Merge in our mental operations: we merge different elements into one, but we also dissect a single element into two (and those in turn may be dissected). Both operations enlarge our cognitive scope: by permitting the formation of new thoughts by means of combination, and by making finer distinctions that produce increasingly refined thoughts. Both are “generative” or “creative”, but along different dimensions of semantic space (inter-concept and intra-concept, respectively).

It might be wondered why thought dissects: what is the point of making concepts ever more acutely distinct? The answer is that finely individuated thoughts are useful thoughts: the distinctions are real and they affect the ability of thought to function effectively in the world. There is a selective advantage to having thoughts with this degree of differentiation: semantic differentiation is biologically adaptive. Thought is relatively crude without it. We may surmise that many animals have thoughts of some kind, but it is also likely that they don’t do well on the score of conceptual differentiation. Some animals may even have the ability to entertain a potential infinity of thoughts, but their thoughts are not chopped as finely as ours. Productivity and differentiation are distinct properties of a cognitive system, so they can in principle be dissociated. And the reason our thoughts differ from animal thoughts in this way is that we have a language rich in lexical distinctions and they don’t. It is estimated that human speakers have mastery of 30,000 to 50,000 lexical items, as well as the ability to combine these to produce indefinitely many distinct expressions for what is intuitively the same thing. Our language consists of clusters of distinct but semantically related words, the result of Dissect. Dissect evolved at some point and it opened up the possibility of creating new conceptual distinctions from old concepts: it took us from an initial relatively crude lexicon to a more sophisticated lexicon rich in semantic distinctions. Thus we became advanced thinkers compared to other animals, and we made adaptive use of this cognitive advance. Dissect is what made science possible, as well as religion, philosophy, linguistics, mathematics, politics, and so on. A creature stuck at the level of purely extensional concepts (or worse) would not have our advanced cognitive powers. Part of this is that more fine-grained concepts are needed for the purposes of explanation—an area in which other animals are conspicuously lacking. In explanation we need to distinguish between different properties of things, not just different things: for example, we need to distinguish weight and mass in physics, species and genus in biology, and belief and knowledge in psychology. One wonders whether there are any such fine distinctions to be found in bee or whale language (and thought).

The standard emphasis on the combinatorial power of language stresses the quantitative results of this power—the sheer number of sentences that can be generated. Thus its utility as a tool of thought rests on its ability to increase the quantity of thoughts a creature can entertain. But the emphasis on the differentiating power of language stresses the qualitative results of that power—the acuity and finesse of the thoughts it can facilitate. It can generate superior thoughts (a normative notion): as Descartes would say, clear and distinct ideas in contrast to unclear and blurred ideas. We obviously value our distinction making capacities, for reasons both practical and non-practical (e.g. philosophy). Not to be able to make sharp conceptual distinctions is a definite intellectual handicap. Somehow the thinking mind taps into the structure of language and uses that structure in acts of Dissectto produce ever more refined conceptual distinctions. It uses distinct words as concept markers, thereby eliciting concept division. That, at any rate, is the hypothesis—though we have virtually no understanding of how the process works, computationally or cerebrally. We know that language serves as a tool in the making of distinctions (or we have good reason to suspect that it does), but we don’t know how it does this—except that it appears to have something to do with the distinctness of words themselves (whatever they are exactly). The lexicon itself is quite mysterious, intrinsically and evolutionarily, and its mental operations inherit that mystery—thus Dissect is shrouded in obscurity. Concepts give rise to other concepts by a process of differentiation, but how precisely this comes about is unknown. Language acts like a tool in the process, but the underlying mechanics are not apparent.  [3]           

 

  [1] Mental images were once viewed as the elements of thought, or at least vital tools of thought. That idea has come in for a lot of criticism and is no longer widely accepted. Although images have some combinatorial powers, it is unclear that they can match those of concepts, which are essentially unlimited. But it is also true that images don’t have the kind of fine-grained individuation that meanings have: several meanings can correspond to the same image (say, an image of a man fishing), and meanings can be abstract in a way that images cannot (as with the abstract concept of a triangle). Images don’t have the right properties to generate fine-grained thoughts, but words do. Language as a formal object consisting of a lexicon and a set of syntactic rules is exactly the right kind of structure to serve as a tool for facilitating thought, because it maps so neatly onto the structure of thought.

  [2] See Robert C. Berwick and Noam Chomsky, Why Only Us: Language and Evolution (MIT Press, 2016). I won’t go into the details of Merge.

  [3] I am not saying Dissect is a permanent mystery, only that our current understanding of it is quite limited. Mergeis also not free of mystery at the psychological and neurological levels, despite its clarity as an abstract set-theoretic operation.