Seeming is a pervasive feature of conscious life. We (and other animals) are constant subjects of seeming: things are forever seeming this way or that to us. It now seems to me that there is a red cup in front of me, that Sebastian is in a good mood today, and that seeming is a worthwhile topic for philosophical investigation. Consciousness could almost be defined by way of seeming: it is a center, a hub, of seeming. What it is like to be x is how things seem to x, and where there is seeming there must be consciousness. Sentience is seeming. Oddly, our vocabulary for it is quite limited: in addition to “seems” we have “appear” and how things “strike” us, but not much else. Synonyms are thin on the ground, despite the ubiquity of the phenomenon (is this a sign of poor comprehension?). What exactly is seeming? It might be thought to be a species of belief, perhaps the tentative kind: if it seems to you that p, then you (tentatively) believe that p. While there is certainly a correlation between seeming and believing, it would be wrong to define the former by the latter, since it is possible to disbelieve what seems to you to be the case (or to be neutral about it). If you have reason to believe you have been hallucinating recently, you may distrust your senses and reject the appearances they offer to your faculty of judgment. Seeming may be something like an invitation to belief, but you can decline the invitation. Nor is belief sufficient for seeming: I believe the Sun is 93 million miles away, but it doesn’t seem to me that way. Seeming looks like a sui generis state of mind, not to be assimilated to belief. It is also shared by different sense modalities and indeed by other modes of knowing: both sight and hearing (etc.) provide us with occasions of seeming, so the nature of seeming cannot be defined in terms of specific types of experience. What we can say is that all knowledge depends on episodes of seeming: we can’t know things without things seeming a certain way to us. Seeming plays a vital epistemological role. What we believe depends ultimately (sometimes directly) on how things seem to us. So it would be good to know what seeming is, how it is to be analyzed. When it seems to me that p what kind of mental state am I in?
The answer might seem straightforward (note how frequently we use the word): I am in a subjective state that has representational content (intentionality, reference). In short, seeming is experience. But that can’t be right as stated, because mental images fit that specification: they are subjective states with representational content, but they are not states in which the world seems to be a certain way. Mental images are not hallucinations and do not present themselves as such. I am not tempted to believe what they represent; they don’t function as evidence for me. Here we might reach for the concept of the sense datum: a seeming is a sense datum, a constituent of perceptual consciousness. This suggestion encounters a problem with non-sensory seeming, unless we enlarge the concept of a sense; but there is a subtler problem, namely that the sense datum, as traditionally conceived, is too weak to add up to real seeming. The intuitive idea is that a sense datum is an intrinsic state of consciousness that transparently presents itself to the knowing subject—not very different from a pain or tickle (“My visual field is yellowish”). But why should that add up to a way the world seems? The sense datum is conceived as a floating element of consciousness—a quale in modern terminology—but where is the idea of how things seem in that conception? Couldn’t such an entity be present in consciousness and not strike the subject as pointing to how things external to him actually are? The sense datum is too neutral, too isolated within itself, too uncommitted. It is too much like an image or idea or concept: it doesn’t carry within it the element of world-directed commitment. It just hangs there. You can see what I am driving at by consulting the dictionary: the OED gives an admirably concise and abstract definition of “seem”—“give the impression of being”. We could choose to build this into the notion of a sense datum, but the traditional notion is not so understood. There are two aspects to the definition: being and impression. Seeming is the appearance of being—existence, reality, externality. It isn’t a neutral quality of consciousness: it points outwards; it has (purported) objectivity. This is more than mere intentionality, since that is compatible with the fictional or subjective status of the intentional object. But in the case of seeming we have apparent reality. When visual experience makes it seem to you that there is red cup in front of you it makes that state of affairs seem real—objectively real, really there. The concept of seeming is connected to the concepts of fact and truth; indeed, it is up to its neck in the idea of an objective, shared, external reality. All seeming is existential seeming (unless explicitly about fictional entities). The senses make the external world real to consciousness (whether or not it really is). If it seems to you that p, then it seems to you that it is true that p (factual, part of being). Seeming is ontologically committed. It isn’t ontologically neutral like traditional sense data or physical stimuli impinging on the sense organs. You need not believe what it purports to reveal, but it certainly has strong opinions (as it were). Seeming is a realist: it affirms the transcendent. The second element is the concept of impression: in seeming you have the impression of reality; you are affected that way. The seeming makes a certain impact on you. Not necessarily a belief, but some sort of mental effect (the word “impress” can mean “make a mark or design on (an object) using a stamp or seal”: OED). You have, as we say, the distinct impression that things out there are thus and so—really thus and so. You may be cut to the quick by this impression, or elated by it, or sublimely indifferent to it. How things seem concerns the self: it is the self that is impressed by the (apparent) encounter with being. But this fact—the fact of having the impression that p—fits none of the standard mental categories, being neither belief nor sensation. It is sui generis and rather puzzling, despite its familiarity. Seeming is neither assent nor feeling, but somehow something in between. It concerns reality and is clear in its commitments, but it isn’t a type of belief—though it functions as an invitation to belief. We might say it belongs to its own mental faculty, alongside the faculties of belief formation, imagination, emotion, etc. It provides input to other faculties but isn’t a special case of them. It demonstrates the variety of the mental (and the dangers of that overarching concept). The seeming faculty is in the business of providing impressions of being (though it can fail in its mission), which we must evaluate in order to arrive at beliefs. These impressions are useful and sometimes impressive (waterfalls, mountains, whales) and no doubt serve a biological purpose. But they are rather mysterious, being neither fish nor fowl. It is hard even to talk about them: we are left with the bare claim that the mind is capable of entertaining impressions of reality that don’t ascend to the level of belief (but do go beyond mere subjective items).
We can now define “seems”, notwithstanding its puzzling status. It seems to an organism that p if and only if the organism has an experience in which it has the impression that p. More briefly, seeming is having an experience-based impression of being. Here we leave “impression” as undefined (the dictionary is no help); it must be taken as primitive. All we can say is that it is not a case of belief (or disposition to belief). Such states, however, are the basis of all knowledge. Hamlet’s famous line “Seems, madam! nay it is; I know not ‘seems’” encapsulates a good deal about seeming: its relation to being and its puzzling status. The traditional philosopher would put “is” after “I know not” (skepticism etc.), assuming that how things seem can be known; but Hamlet seems (!) to be saying that he doesn’t know anything about seeming. What is this strange seeming, this curious hybrid, this committed agnostic? I understand “To be or not to be”, but what are we to make of “To seem or not to seem”? I know not that, Horatio. Poor Hamlet, he doesn’t even know how things seem, let alone what really happened to his father or the nature of the afterlife! Our ordinary language also seems to be in some doubt on the matter: there are verb and adjective forms of “seem” (“seems” and “seeming”), but there is no noun form, as if English is reluctant to engage in the ontology of seeming. I have spoken in noun form of “a seeming” and “seemings”, as if there are such things, but that is not regular English. English, like Hamlet, knows not “seemings” or “a seeming”. Yet seeming seems real (I have the strong impression that seeming has being)—there are seemings of seemings. But they are puzzling conceptually; perhaps this is why they are seldom discussed, or assimilated to something else. We need a philosophy of seeming (not of physical sensory inputs or amorphous “sense data”); in particular, we need a better understanding of the notion of “impression”. Perhaps seemings are supervenient on other mental phenomena such as experiences of one kind or another, but we should be wary of any attempt to reduce them to such a basis. Do experiences cause seemings? Is it because of experiences that things seem a certain way, even though seemings strictly transcend experiences as such? Or are the things we call “experiences” really compounds of seeming and some more primitive sensory material? And how do experiences make an impression on the subject, whatever that effect is exactly? Hume spoke of impressions and ideas, recognizing that the senses do more than just parade ideas before our minds, but he said nothing to explain what an impression is, i.e. what it is an impression of and what it is an impression to. We are constantly having impressions of this or that, but what this operation amounts to remains obscure. Metaphorically, it is something like an imprinting (a type of denting), but that tells us little of any theoretical use. All knowledge therefore rests on something we don’t understand.
 Someone might try saying that seemings are the beliefs of the perceptual modules, potentially in competition with the beliefs of the central system, as in cases of visual illusion (see Jerry Fodor’s The Modularity of Mind). But that is an anthropomorphic picture of the perceptual systems: nothing in you believes that the lines of the Muller-Lyer illusion are unequal (assuming you know the illusion). The seemings of the senses are completely non-doxastic. It is merely as if your visual system believes what it delivers. Belief is really the icing on the cake not fundamental epistemological reality.
 If we say all knowledge rests on observation, we tacitly bring in the idea of seeming: an observation is a mental act in which something seems to be the case. That is, observations are precisely conscious states that embed an impression of being: the observer is affected by reality in a certain way and he seems to himself to be so affected. We can’t avoid admitting seeming into the epistemological picture in favor of something (seemingly) less obscure. Seeming is inescapable.