Big Mystery: Space and Time

What is the most fundamental mystery in the universe? Mind and matter is big, but space and time might be bigger. Each individually is a mystery, as has long been recognized, but there is also the mystery of their connection. How are space and time connected? Are they connected? It might be held that they are separate realities, merely existing alongside each other (“alongside” in what sense?), different in nature, only contingently connected. You could have one without the other: in some possible worlds there is space without time and in others time without space. Why should space require time in order to exist, or time require space? Aren’t they like chalk and cheese or electricity and gravity—distinct existences (to use Hume’s phrase)? Space has three dimensions (possibly more), time has just one; space is extended, time is not; space is static, time flows. When God created space he hadn’t even thought about creating time, and he could have created time without creating space. So it seems: we have such “intuitions of contingency” (compare mind and body). I open my eyes and see space, but I don’t see time (perhaps I feel it in myself); I experience the passage of time (memory, expectation), but I don’t experience the passage of space; I can get lost in space, but can I get lost in time? We apprehend space and time quite differently, and this seems grounded in metaphysical differences: so isn’t there a fundamental dualism here? Not a dualism of the material and the immaterial, but a dualism of the spatial and the temporal: the essence of space is extension (trivially), while the essence of time is continuation (the onward march). We are dealing with two sorts of “substance”: spatial substance and temporal substance (we could also say “stuff” or “quiddity”). It would be crazy to try to reduce one to the other: to claim that space reduces to time or time reduces to space. Such a view would be flagrantly eliminative, false to the facts. So space-time dualism seems the indicated position: non-identity, non-supervenience, non-reducibility. We should be “Cartesians” about space and time.

            But this position faces nagging questions (just like mind-body Cartesian dualism). Are space without time and time without space really conceivable? Might there not be “illusions of contingency” here? Is it an accident that both are infinite (infinitely extended and infinitely divisible)? And don’t the two “interact” in certain ways? Material objects exist in both space and time, having both location and history. They could hardly exist in one but not the other: there couldn’t be objects in space that have no history (what kinds of objects would these be?) or objects in time that have no location (where would such objects be?). Material objects straddle space and time, having a foot in both camps. Isn’t causation essentially spatiotemporal? Causation requires contiguity in space and time (or spatial separation in the case of action-at-a-distance). And motion is defined in terms of space and time: how much space is traversed in how much time. These are points of “interaction” between space and time, analogous to perception and action in the case of mind and body. Space and time seem designed for material objects, their sine qua non; so it isn’t as if they never recognize each other’s existence. They cooperate in various ways—as when an organism is born in a certain place and then lives a life over a certain period of time. We also measure space and time using the same kinds of measuring device, viz. physical objects (rods, clocks). Don’t physicists speak of “space-time” and treat both as basically physical? Space is treated as constituted by relations between material objects, and time is regarded as equivalent to periodic processes such as rotations, orbits, and oscillations. This may be found unduly verificationist, but doesn’t it indicate a degree of affinity, commonality? The idea of space without time or time without space will strike physicists as pure mythology, not consistent with Relativity Theory (their touchstone of truth). All in all it appears that space and time can’t be quite as separate as our imaginations may suggest; and yet reducing one to the other seems preposterous. A double-aspect theory suggests itself, obscure as that may be (space and time as two sides of the same coin). The situation resembles the usual dialectic surrounding mind and body, with the same array of (unattractive) options.

            We seem headed toward a mysterian position: space and time are intimately connected, necessarily so, but the connection is opaque to us, really opaque. The spatiotemporal “link” is not given to us; there is an “explanatory gap”; and we suffer from “cognitive closure” about the space-time nexus. This may arise from deep ignorance about what space and time are: we just don’t have penetrating knowledge about the nature of these things. Our conception of space is just a patchwork of superficial sensory representations combined with some mathematical artifice; our conception of time is conditioned by the practical concerns of life plus some rudimentary methods of calculation (calculus, for instance). It’s all maps and clocks, basically. We just don’t know much about the real objective deep nature of space and time, so we flounder in our understanding of how the two relate. Some may resort to the analogue of panpsychism: maybe there are little bits of time in all parts of space, or specks of space locked inside all instants. Others may boldly go eliminative (that seems to happen a lot with time). Dualism seems like the commonsense position, but commonsense is often limited when it comes to big cosmological questions (animal minds like ours are not cut out for cosmology given that food and shelter are our paramount concerns). Thus it may be that the nature of space and time lies largely concealed from us, generating misleading intuitions of contingency and impressions of ontological distinctness. Could there be some deeper reality of which space and time are merely aspects? Is this reality knowable by us? In the case of the mind-body relation we do have some relevant knowledge: we know that the brain is vital, that minds evolve and change with bodies, that there are causal relations between the two (often quite specific and intricate). But we have difficulty making sense of this knowledge, creating a viable theoretical edifice out of it. In the case of the space-time relation, however, we don’t even have even this primitive level of knowledge: all we know is that space and time come together in material objects (“the bus was going 30 miles an hour”). We don’t have systematic correlations between space and time, or causal relations, or an analogue of the brain (which at least gives us somewhere to look). We just have broad theoretical reasons for thinking that space and time must have some sort of underlying connection–it can’t be just an accident that they exist together. This is why I say that the mystery of space and time may be bigger than the mystery of mind and body: space and time are bigger in themselves, of course, and we draw an even bigger blank when contemplating their ultimate relationship. They must be connected, yet they seem radically unconnected. Thus we feel queasy when asked to consider their metaphysical separation (as in those alleged possible worlds that have one but not the other), but we are compelled to admit that we have no account of their necessary connection. Perhaps we are convinced that both are necessarily connected to matter (no space without material objects and no time without concrete events), but we hesitate over the question of radical ontological separation. For in virtue of what are the two necessarily connected, and how can they be so connected if they are what they seem? Time is one thing, space is another—how do the two manage to meet in the middle? Did God just slap them together or did he engineer an intelligible interlocking machine? Is the cosmos ultimately made of SPIME? Space stretches out and time ticks by—what have these facts go to do with each other? What is the meaning of their coexistence? Why must a universe be made like that? These are Big Mysteries, even bigger than the “world-knot” of the mind-body problem; we could call them the “cosmic-maze”. We are locked in the maze of space and time trying to find our way out, as we have both a mind and a body and struggle to untangle the conceptual knot they present. We can’t solve the maze and we can’t untie the knot—hence the mystery. But in both cases we can be sure there is a solution out there, even if we can’t produce it ourselves. Space and time fit snugly together somehow, as mind and body also do. We just have a boatload of trouble (possibly terminal) figuring out how the connection works. When I think of space my mind naturally turns to time, and when I think of time my mind naturally turns to space; and I have faith that space and time echo my thoughts in their own way. It’s just that I’m not privy to the way they join together. I have a vague feeling that time infuses space, peps it up, like alcohol in wine; and a feeling that space gives substance to time, beefs it up, like yeast in bread. But I have to confess that I have no idea what I am talking about when I say such things. I just feel that the two belong together in creating a fuller, more complete, world—that they are sadly lacking without each other. Each fills out what would otherwise be intolerably etiolated, hardly meriting the name “reality” at all. But maybe that’s because I would not exist but for their mysterious union: for I know myself to be a creature of both space and time. (Here philosophy makes contact with poetry, to which it is actually quite close, despite the appearances presented by your average philosophy department). If space and time were not connected, the universe would be genuinely meaningless—just static emptiness and transitory futility. Space would have no history and time no point (is there anything more desolate than the idea of time without even space to play with?). Space and time need to mesh if anything is to mean anything.[1]                        

[1] Mathematical existence, conceived Platonically, is absent space and time, and perhaps there is a possible world limited to such existence; but it would be a bleak and arid world, despite Plato’s fondness for it. Numbers can’t even move (or be at rest)! What there can’t be is a possible world containing only time or only space—such a world is a mere chimera, though suggested by the appearances (or some of them). Space and time necessarily come as a package deal.

Empiricism and Semantic Knowledge

Empiricism tells us that all knowledge worthy of the name derives from the senses. In Hume’s formulation, every idea has its origin in an impression, such as an impression of red. This is a psychological theory to which empirical evidence is relevant (what if we came across a whole batch of ideas that exist without benefit any prior sensory impression?). It is not intended as a logical or conceptual truth: there is nothing in the concept of an idea that entails that ideas must derive from impressions. That is why Hume conducts a survey of ideas to determine whether his general principle is correct. Notoriously, he runs into apparent counterexamples: not only the missing shade of blue, but also ideas of causation, the self, space and time, persisting bodies, and number. But he never (so far as I know) faces up to the case of semantic knowledge—what he would call ideas of meaning. We clearly have such knowledge: we know what the words of our native language mean and we can learn the meanings of words used by foreigners. Meanings are objects of cognition: we can think about them, ascribe them to marks and sounds, reason concerning them, have arguments over them. We know them as well as we know colors and shapes (the empiricist’s favorite examples). I know that “snow is white” means that snow is white—does anyone contest that? But how do I have such semantic knowledge—do I have it by means of sensory impressions of meaning? I hope the answer to that is a resounding No: when I hear someone speak and know his meaning I have no sense impression of meaning (I do have impressions of the sounds he makes). If I did, I could understand people speaking a foreign language without laboriously learning it—I could just sense what they mean. It would be like seeing a new combination of colors or hearing a new series of sounds—the senses would have it covered. There is thus no such thing as an impression of meaning in the sense intended by empiricists. This is as true for one’s own meaning as much as it is for other people’s meaning: I don’t have an impression of what “red” means to me. There are no sense impressions of senses, my own or other people’s. I don’t have sensations of meaning. I know about these things, but not because I sense them with my senses. If “impression” means “sense impression”, and these are limited to what the five senses convey, then we have no impressions of meaning. No child embarking on the business of learning language is ever confronted by an impression of meaning from which he or she derives ideas of meaning. Nor has anyone ever suggested such a thing—because it is obviously mistaken. So empiricism is false for the acquisition of semantic knowledge. Meaning belongs with those other ideas that resist the empiricist dogma: causation, the self, persisting bodies, etc. But in the case of meaning it is even harder to dispute whether the ideas in question are really possessed (do we really have an idea of the self?): we indisputably do have semantic knowledge, semantic concepts, and semantic thoughts—but without antecedent semantic impressions to ground them.

            You might try claiming that our knowledge of meaning is theoretical: we infer meaning from other types of impression. It is hard to see how this will go but a suggestion that has found some traction is ostension: we have impressions of pointing. The index finger extends in a perceptible dog-containing environment as “dog” is intoned, and an observer can have an impression of this performance—you see dog-oriented pointing going on and infer the meaning of “dog”. There is no need for me to critique this theory, given the obloquy it has been forced to endure, but I will say that an impression of pointing (the stiffened index finger in line with an object) is hardly sufficient to generate an idea of the meaning intended. The impression is far removed from the semantic information it is supposed to impart; you may as well say the expression on the pointer’s face is the basis of the meaning he intends. Many beings (e.g. dogs) could be witness to such a performance and yet have no knowledge of the meaning of “dog” as a result of it. As the native extends his finger while uttering “gavagai”, the field linguist is still in doubt about what that word means. But even if knowledge of meaning could be gained from such impressions, the fact remains that meanings themselves are not perceptible. The first-person knowledge the linguist has of her own meanings is not impression-based either. Moreover, there is a strong feeling that meanings could not give rise to impressions: meanings are not the kind of thing that produces impressions—like numbers (and unlike molecules). It is a necessary truth that meanings are imperceptible. In any case our actual knowledge of them is not impression-based, i.e. acquired by means of direct observation of their nature (by “acquaintance”). Rather, ideas of meaning are brought to perceived utterances, not derived from such utterances. Where these ideas do come from is not so clear: they could be innate, or they could be created by the developing child in some way. They could also be a mixture of the two, as much of our knowledge undoubtedly is. But what an idea of meaning can’t be is a “faint copy” of an antecedent impression, or be “abstracted” from an impression of meaning. There are no impressions of meaning that could form the basis of our knowledge of meaning in the manner envisaged by the empiricists. Meanings themselves are right there before us, so to speak, but they don’t show up in consciousness as Humean impressions.[1]

            Accordingly, knowledge of analytic truth can’t be impression-based: you don’t have an impression of the meaning of “bachelor” and an impression of the meaning of “unmarried male” and notice that these impressions are identical. Yet you have genuine knowledge here, just not empirical knowledge. If it were based on semantic impressions, it would be empirical: but as it isn’t, it ain’t (as Lewis Carroll once said). So knowledge of meaning is a powerful counterexample to empiricist epistemology, yet seldom if ever cited in this connection. And if the correct theory of it is that such knowledge is either innate or created (or a combination of the two), then this theory might well be the one to adopt for other types of knowledge too, such as knowledge of color and shape. Impressions of red might merely elicit our innate concept of red, rather than being the basis on which we acquire that concept ab initio. At any rate, we don’t come to know meaning by having impressions of meaning fed into our minds.

[1] If they did, theory of meaning would be a lot simpler: we would have direct knowledge of the nature of meaning.

Existentialism and Essentialism

The existentialist credo is: Existence precedes essence.[1] This stands opposed to the dictum: Essence precedes existence. It’s Sartre versus the Scholastics, supposedly. Sartre’s existentialism, deriving from Kierkegaard and Heidegger, is said to invert traditional metaphysics, which takes the nature of a thing to be prior to its existence—or at any rate to be coeval with it. There can’t be existence without a corresponding constitutive nature—a set of defining properties. The existentialists apply the contrary doctrine to human psychology: the mind is initially a vacuity that is subsequently filled by radically free acts of will. Sartre’s says it is Nothingness: an empty potentiality, a mere receptacle, with no internal content or structure. This result is said to derive from the structure of intentionality, which is conceived as pure directedness to an object. In particular, the mind contains neither a moral sense nor a personality that determines what the agent will do—not until such things are freely chosen. A thesis about human psychology is thus held to derive from a metaphysical principle—the principle that in the case of the human mind existence (being) precedes essence (nature). Whether animal minds also conform to this principle we are not told (how could they not given the biological continuity?); at any rate, the human animal has no definition or nature qua psychological subject—except the absence of a definition or nature. We are “condemned to freedom”, as Sartre says, because our existence is metaphysically prior to our essence—we exist as pure possibility.

            I don’t intend to discuss the details of the existentialist account of human reality; I want to note its affinity with other doctrines of similar metaphysical stamp. I am concerned with the underlying metaphysics of existence and essence (which is not to be understood modally but as meaning something like “constitutive nature”): for there is a striking analogy to other doctrines seemingly at some remove from the concerns of the existentialists. First, empiricism: the theory that the mind is initially a tabula rasa, a blank, slate, or an empty cabinet. There is no innate knowledge, nothing cognitively given at the outset. The existence of the knowing mind precedes its having any substantive nature, save that of its constitutive blankness (even a sheet of blank paper has some nature—just nothing worth reading). The mind acquires knowledge by interacting with the world, both personal and impersonal—just as Sartre thinks that we acquire a moral sense and a personality by interacting with the world outside the mind, particularly other people (also initially empty receptacles condemned to freedom). The mind is free to acquire whatever comes its way without any prior determination from inside, whether cognitive or moral. The nativist, by contrast, views the mind as initially richly structured, full of content, but limited in its possibilities—rather like the body. Similarly the essentialist about the self thinks that human personality and moral sense are fixed by factors outside of our control—genes or upbringing or God’s benevolent design. Action is the result of these not their cause, as innate knowledge is held to enable the later acquisition of knowledge (in conjunction with input from outside). The dialectical picture is the same in both cases: either the mind is empty potentiality or it comes already equipped with a nontrivial nature, understood as a type of knowledge or a type of character. Traditionally, God is supposed to be the author of the innate essence of the human soul: it is he that gives us a moral sense, a particular psychological makeup, and a set of innate ideas. So mental essentialism goes with theism in traditional thinking: how else is human nature determined? As against this conception, the existentialist has no need of God to explain the installation of a mental essence, since there is no such thing. The atheist therefore has no theoretical need of God to confer an essence on the human soul; and indeed to suppose there is such a thing is to court theism as a theory of how such an essence comes to exist. We don’t need God to explain how the human mind has this or that in it at birth since it has nothing in it: blank slates need no contribution from God. In an atheistic world a lack of design and determination is only to be expected—or so it is supposed. Thus existentialism and empiricism make natural partners, as do essentialism and nativism. And just as empiricism liberates us from a scholastic and theistic past, so existentialism is supposed to liberate us from an outdated metaphysics and reliance on God as an explanatory crutch. Sartre could have cited Locke as his enlightened forerunner—his epistemological existentialist (epistemic existence precedes epistemic essence).

            But that is not the end of the analogies: we also have the bare particular, the featureless substance, and the indeterminate substrate—matter without form. That is, we have the metaphysical doctrine that corporeal existence precedes physical essence. Here the picture is that the physical world is based on a kind of undifferentiated mass or stuff that is shaped into actual objects of determinate kinds by imposed forces. Call this stuff “matter” with no commitments about how it is articulated: then matter in this sense is the counterpart to the blank slate of Locke and the empty consciousness of Sartre. It is what physical reality is before form gets to work on it (maybe what preceded the big bang). It is bare matter, matter without determinate properties: pure potentiality not definite actuality. Some people (e.g. Heisenberg) describe the quantum world this way, suggesting that we must liberate ourselves from the old picture of a fixed determinate reality. Maybe so-called matter is really energy, conceived as an amorphous field of potential action—not particles occupying specific locations and moving in determinate ways. In any case, it is supposed that we have an idea of a non-individuated physical reality that precedes formation into natural kinds and determinate objects (“All is formless gunk”, as a pre-Socratic might say). This is physical existentialism (did quantum physics influence Sartre?). Once such a view has been taken on board, we can envisage a grand metaphysics of generalized existentialism: all of existence precedes essence—everything is initially a malleable Nothingness, pure potentiality.[2] All reality is in the first instance a blank slate: it needs input from outside in order to possess a nature (free action, sensory stimuli, or quantum measurement). Without these external influences it would remain at the level of empty potentiality, a void, a vacuum, an absence. That is the new metaphysics that is to replace the old mythology of a cleanly defined, divinely ordained, cut-and-dried world of delineated objects—the world of primordial essences. Not orderly civilized essence but raw wild existence rules the world. No God in his right mind would create a world of the latter kind, but that’s okay because God is dead—or so the existentialist believes. The global existentialist views the world as consisting fundamentally of two kinds of formless material, mental and physical; such form as it may possess is the outcome of extraneous forces. Intrinsically, reality is made of Nothingness.

            How good is this metaphysics? Is it intelligible? What exactly is existence without essence? How can something exist and yet have no nature? Various metaphors and analogies have been ventured, some used already by me in an attempt at exposition: blank slate, empty cabinet, undifferentiated stuff (or lump), bare particular, vacuum, void, absence, Nothingness, emptiness, plastic, putty, mathematical point, etc. But these all fall short of aptness and clarity, mainly because they are never blank enough—they always have too much structure, too many properties. And the idea that something could exist—really exist—and yet have no nature seems to make no sense. Existence and essence go hand in hand—you can’t have one without the other. Even the empty set is a set and is empty! In the case of the human mind there are clearly many natural properties that a mind possesses the moment it begins to exist, even if these are just a general ability to learn by mimicry and conditioning (and we know there is much more to it than that). Human beings have instinctual needs and desires, innate emotional responses, and inborn cognitive capacities: there is nothing blank about them. Nor is the pure potentiality view of quantum phenomena compulsory (Bohm’s hidden variables, etc.). I won’t go into the details, but there are well-known empirical and conceptual objections to the “existence precedes essence” mantra. I suspect a powerful motivator here is the feeling that essentialism requires God: how else are we to explain why the world is naturally arranged one way rather than another? But we can surely make room for an atheistic acceptance of the actualities of existence: we have evolutionary explanations of inborn human traits as well as alternative accounts of quantum phenomena. The natural and simple view is that everything that exists has a nature, more or less intricate, with which it confronts the world outside. It is true that you can say that a thing exists without incurring any commitments as to its properties, but it doesn’t follow that a thing can actually exist and have no properties: one point is linguistic, the other ontological (does the metaphysics behind existentialism rest on a use-mention mistake?). The idea that existence could characterize an object and yet the object has no further properties is surely incoherent (what kind of object would that be?). Sartre’s description of consciousness as Nothingness is clearly an exaggeration even according to him, since consciousness is held to have intentionality as its essence—a pretty substantive property. And Locke’s blank tablet is precisely a tablet with the power to receive inscriptions and preserve them. Nothing could have only the property of existence. I take it this is crushingly obvious and hardly worth stating, but the charm of the (alleged) idea of property-less existence is apparently so strong that common sense has trouble stifling it. It seems to be one of those romantic semi-ideas that irresistibly surface in the human mind despite its hazy credentials—like the idea of immaterial spirits, ghosts, and suchlike. Maybe the womb was experienced as a kind of bland nothingness—the null environment? The idea is essentially mystical, evoking images of mists and magic. That is the reason for its appeal: the charm of the supernatural in the shape of shapelessness (the “holy spirit”). In the state of Nothingness we can free ourselves of the body, perhaps even achieve immortality (how can you kill Nothing?). Whatever the source of the notion is, it hardly makes for a coherent metaphysics. Things necessarily have a nature and this nature limits (and enables) them—bodies, minds, and elementary particles. Existence can’t precede essence; it can only manifest it. If so, existentialism is false.

[1] This formulation comes from Sartre’s 1945 “Existentialism is a Humanism”. It sounds like a piece of analytical philosophy that might be found in Kripke’s Naming and Necessity (1972).

[2] Mathematical objects would be the exception, since the idea of mathematical stuff makes no sense. In the realm of numbers existence does not precede essence, even for the staunchest existentialist (though I suppose we can envisage an anti-essentialist willing to go even this far). On the contrary, it is the idea of an existence beyond essence that seems to have no application to numbers—they have no being but essence.

Intentionality and Space

Here is a famous passage from Brentano’s Psychology from an Empirical Standpoint (1874): “Every mental phenomenon is characterized by what the Scholastics of the Middle Ages called the intentional (or mental) inexistence of an object, and what we might call, though not wholly unambiguously, reference to a content, direction toward an object (which is not to be understood here as meaning a thing), or immanent objectivity. Every mental phenomenon includes something as object within itself, although they do not all do so in the same way. In presentation something is presented, in judgment something is affirmed or denied, in love loved, in hate hated, in desire desired and so on.” (92-93) There is not a little obscurity here and many readers have fastened onto the last sentence as something clear to hang onto. But if we are to understand Brentano’s thesis we need to scrutinize the explanatory phrases with which he introduces the idea of intentionality. First “intentional (mental) inexistence”: this is not to be taken to mean “intentional (mental) non-existence”—it isn’t the idea that intentional objects don’t exist. It is the idea that they exist (reside) in the mental phenomenon: they are contained in it, are a constituent of it. Brentano alternates between “inexistence” and “in-existence” without explaining why (and neither do the translators comment on it), but the latter expression better captures what is intended, namely existence-in—what is also called immanent existence (immanent in the mental phenomenon). Next we read that this trait could also be called “reference to a content”, which introduces two new notions: reference and content. The first word suggests language and speakers, which cannot be what is literally intended, since it is not supposed that all intentionality springs from language: the mind isn’t linguistically referring when it contains an object (not according to Brentano anyway). The second word suggests some sort of conceptual representation, analogous perhaps to Frege’s notion of sense; but that can’t be right because the intentional object is more like a reference than a sense—an object not a concept. And Brentano later dropped this formulation, no doubt for the reason just stated: of course the content of a mental phenomenon is immanent in it; what is being claimed, more controversially, is that the object is immanent too. Immediately following we have the phrase “direction toward an object”, as if this were a mere paraphrase of the previous expression, which it clearly is not. The phrase “direction toward” is presumably a metaphor (but see below), and has been latched onto in subsequent writing; and the notion of object is clearly meant to connote the target (another metaphor) of a mental state—what it is about. Hence an object in this sense is not a “thing”, by which is presumably meant a denizen of the mind-independent world (a plant, an animal, a rock). Here “object” is used as it is in “object of thought”, i.e. entity thought about. We are then faced with the daunting phrase “immanent objectivity”, which could use a little unpacking (to put it mildly). The thought is that a mental phenomenon immanently (intrinsically) contains object-directedness—it is object-oriented, object-specifying. There is something object-like lurking inside the mental state. Immanence here contrasts with transcendence, i.e. existence beyond the mental state: the intentional object is not extrinsic to the mental state but right there inside it. As to “objectivity”, this is not intended to suggest real existence outside the mind, but rather the object-positing activity of the mind (Brentano doesn’t use the word “posit” in this connection, unlike his descendant Sartre). The object of a mental act is what is presented to the subject in consciousness (“presentation” is taken by Brentano to be a universal feature of the mind). Interestingly, in a footnote to the later “Attempts to Classify Mental Phenomena” (p.189) Brentano tells us that he had considered using “objectivity” to characterize the feature he wishes to identify instead of “intentionality”, because the latter misleadingly suggests the ordinary notion of intention; but then he reflected that “objectivity” would be equally misleading, suggesting to modern readers the idea of “what really exists as opposed to ‘mere subjective appearances’”. He notes that we have no ordinary-language word for the universal and salient feature of mental object-directedness, itself a peculiar fact, and that no technical term is free of difficulties. One might suggest that a neologism like “objecticity” or “objectality” might serve the purpose, but these too court misunderstanding; we may as well settle for “intentionality” despite its misleading connotations. Anyway the phrase “immanent objectivity” should be taken to mean the same as “immanent intentionality” in Brentano’s mouth: the object intended (sic) is in the mental state not outside it (not transcendent). As he says: “Every mental phenomenon includes something as object within itself”.

            Readers have tended to focus on the object-positing aspect of Brentano’s notion of intentionality, and indeed it is striking and plausible, neglecting the thornier concept of intentional in-existence, i.e. object-immanence. This has enabled later theorists to avoid what looks like a tension in the notion, indeed a contradiction. For how can we reconcile the following two theses: (a) the mind is always directed toward an object distinct from itself, and (b) the objects of mental activity are always within the mind? How can the intentional object be both outside and inside the mind at the same time? How can it be both transcendent (not identical to the mental act that posits it) and yet also immanent (strictly within the mind)? Perhaps this difficulty explains Brentano’s early equation of object and content: the content is clearly immanent, which satisfies one aspect of the intentionality doctrine, but then we lose the idea of separateness from the mental act itself. Compare qualia: they are clearly immanent (on most ways of construing them), but they are not distinct from the mental state that harbors them. On the other hand, the external physical objects of perception are clearly distinct from perceptual experiences, but they are scarcely immanent in such experiences. The intentional object is called upon to be a bit of both—part immanent and part transcendent: hence Brentano’s equivocation. And yet the underlying notion seems entirely correct: if I am hallucinating pink rats, say, these perceptual objects serve to individuate my experience, and yet they are not the same as my experience (it isn’t pink and ratty). The question is how to characterize this fact accurately. I don’t think Brentano ever succeeds in doing this despite the basic correctness of his theory. He has hold of a datum but he doesn’t have a clear and coherent characterization of it. You might try saying that the object is part of the experience (not identical to it), but this too is obviously wrong—no part of my hallucinatory experience is a pink rat either. The identity of my experience is fixed by its objects but it is not identical to its objects—hence immanence combined with transcendence. There are ways to go here but they require a closer examination of the nature of intentional objects—are they perhaps combinations of universals?—but the task is not an easy one. In any case, Brentano’s introduction of the concept of intentionality stands in need of further work, sound as it may be in fundamentals. What I have wanted to bring out is the tension inherent in his formulation of the notion, which is revealed when we press hard on key phrases, particularly “immanent objectivity”.

            With these clarifications in place I now want to focus on a different (but related) question: the role of space in constituting the structure of intentionality. In the most basic case the distinctness of the intentional object (hereafter the Object) consists in separation in space, i.e. perceived separation. We see the object as spatially removed from us, and hence distinct. The Object is phenomenally distant (even if it doesn’t in point of fact exist). Perceptual presentation is presentation in space. Even bodily sensations are spatially presented: the pain located in the foot, the tickle under the arms. So the Object is not presented naked, as it were, but as embedded in a spatial matrix. Even thoughts are positioned in relation to the body, roughly in the vicinity of the head. Space is the form of our sensibility, as Kant would put it. It is notable that Brentano’s most explanatory phrase, and the one that is most often repeated, uses a spatial concept—that of direction. We do indeed experience Objects as existing in a certain direction, and we direct our attention to certain portions of space. It is the same with the notion of pointing, also natural in this connection (but not used by Brentano): one points in space. The separateness of the Object is typically (paradigmatically) a spatial separation: we experience things as spatially distinct from us. We might even suppose that phenomenal space is a precondition of intentionality; it is certainly ubiquitous.[1] Then the following thought comes to mind: the mental and the physical are not quite so different from each other as we might have supposed. For if the essence of the physical is extension, then the essence of the mental is phenomenal extension. Material objects stand in spatial relations and are extended in space; mental phenomena are intentionally directed to Objects in (phenomenal) space. Space thus enters in two ways into the constitution of reality: as the condition of material existence and as the condition of mental existence–the former by way of actual physical space, the latter by way of perceived phenomenal space. Things in actual space are not intentional in virtue of properties of extension; things not extended in actual space nevertheless incorporate space into their intentionality. The material world is extended but not directed toward extension, while the mental world is directed toward extension but not extended. So the mental and the physical are not quite so sharply distinguished as Brentano’s criterion would suggest, once we take account of the role of space in constituting intentionality. An idealist about space might suppose that actual physical space derives from phenomenal space; a realist about space might suppose that phenomenal space results from actual physical space by some sort of abstraction or by dint of outright externalism about mental representation. But even if we recognize two irreducible sorts of space, it turns out that space is the common factor between extended matter and non-extended intentional mind. There may indeed be two fundamental sorts of reality, extensional and intentional, but they are united under the umbrella of space: one existing in space, the other having space existing in it. Space (as Object) is immanent in the mind, as well as being distinct from mind, and it is also immanent in matter (but not as Object). There is a dualism of spaces here that goes along with the dualism of the extensional and intentional. Brentano talks as if the structure of intentionality exists independently of spatial representation, so that mind and matter are conceptually and ontologically remote from each other; but once we recognize that space is integral to both we see that the two are not so widely separated.[2] To put it differently, the mind is as reliant on extension as matter is in order to have being, despite the different ways in which extension enters the picture (de re and de dicto, as it were). And it is extension that grounds the “objectivity” of intentionality, because the mind is “directed” to things in phenomenal space: the intended Object is located in space relative to the subject. I see pink rats as over there, at a certain distance from me, and this is what my apprehension of this Object as distinct (transcendent) is grounded upon. The immanence consists in the fact that this remote Object also individuates my mental state—the remote fixes the proximate. Without perceived space it would be hard to see what the distinctness of the Object could consist in, so Brentano is tacitly relying on it to ground intuitions about the intentional structure of the mental. But then he is invoking a type of fact that applies also to the physical world, only non-intentionally. It is true that there might be peripheral cases in which matter is not extended and mind is not embroiled in the spatial, but surely the central cases both involve extension in their respective fashions. Descartes taught us that the essence of matter is extension; Kant taught us that the essence of sensibility involves “intuitions” of space; Brentano taught us that the essence of mind is intentionality: put these all together and we get the result that matter is constituted by real extension and mind is constituted by phenomenal extension. Mind is directedness toward a spatially extended world, and matter is that world (granted that it exists). Physics is the study of the actually extended world; psychology is the study of mental phenomena about the (phenomenal) extended world. Mental phenomena are essentially intentional; the intentional is spatially saturated; so psychology is about mental reference to a spatial world. It is about aboutness, and aboutness is spatially constituted. The laws of psychology therefore concern spatially imbued intentional states (e.g. the laws of psychophysics). We can abstract away from phenomenal extension in psychology, as we can abstract away from actual extension in physics, but the subject matter is inextricably bound up with extension in both cases. In particular, the mind is inherently intentional in Brentano’s sense (suitably cleaned up) and up to its neck in spatial representation. So there is a kind of metaphysical unity at work here despite the deep ontological differences between the mental and the physical.

[1] It might be thought that mathematical intentionality is a counterexample to the claim of spatial universality, since we don’t apprehend numbers as existing in space. Mathematics is a special case in many ways, and its ontology is highly debatable, but I would note the following point: we do apprehend numbers as public objects in the sense that the same number can be grasped by many minds (unlike particular states of mind). This is an analogue of spatial separation because it locates numbers in a “space” beyond the mental sphere—hence the talk of “logical space” and “Plato’s heaven”. We can’t help thinking of mathematics in quasi-spatial terms, so even here spatial concepts condition our thinking. But in the case of concrete reality, both mental and physical, space holds sway: here intentionality is candidly spatial in nature. Brentano would have done well to acknowledge this fact explicitly, especially since it would enable him to make his points more clearly and decisively.   

[2] Brentano talks as if intentionality were a one-at-a-time thing, but in perceptual cases (and arguably in others) there is a kind of intentional clustering: the mental act takes in many Objects simultaneously, as with vision. Many Objects are laid out in space and intentionality arranges them thus-and-so. Also, it seems wrong to view it as an all-or-nothing thing: we can be more directed to one Object than another, as with the center and periphery of the visual field. Intentionality is not a simple one-one on-off relation (or quasi-relation) but operates more holistically and in a graded manner. What is right in his idea is that the mind is intrinsically directed at the world, though in manifold ways. This is a rather startling discovery because otherwise the mind is quite various (Wittgenstein would have done well to take note of it in his insistence on psychological variety).