Imagine coming across a tribe with the following peculiar epistemic deficit: they are strangely ignorant of ordinary familiar things like animals, people, mountains, and other objects in the environment. They don’t know whether cats and dogs are both animals, they don’t know whether mountains are convex or concave, they don’t know the color of leaves, they don’t know the shape of the human body, they don’t know whether humans have minds, they don’t know that the sun is warm, etc. Their senses are normal and they know about many things (perhaps they know a lot of mathematics and history), but they draw a blank on questions that concern things they interact with every day. We find this very strange, a peculiar kind of selective ignorance. Perhaps we start to suffer from a similar pathology after a time and eventually trace it back to drinking from a certain river; we therefore assume an underlying physical cause. In any case, it is an ignorance quite unlike the kinds with which we are already familiar—such as things being too far away or too small to see or hidden in some way. We dub it “strange ignorance syndrome”.
I want to compare this with our situation in regard to philosophy. The things that trouble us are ordinary familiar things not remote or inaccessible things: perceptual objects, consciousness, the will, the self, numbers, causality, values, universals, space, time, necessity, and so on. And we are ignorant of fundamental properties of these things: we don’t know their basic nature. Consider ordinary physical objects: we know they have color, shape, location, etc., but we don’t know whether they are mere bundles of qualities, or whether they exist in the mind or in a mind-independent way, or whether they really persist through time. You can stare at such objects from dawn till dusk and examine them from every angle but you will not thereby be able to answer these questions. As we like to put it, you can tell the shape and color of an object but you can’t tell its ontological status. Similarly, we know many properties of consciousness but we don’t know whether it is identical to the brain: you can tell you are in pain but you can’t tell whether pain is a brain state. That’s why we resort to arguments in philosophy—because we can’t simply tell whether pains are as one or another theory claims. I can tell by introspection that my pain is throbbing but I can’t tell that it is a brain state (or a state of an immaterial substance). Likewise, I can’t tell whether universals are mental, abstract or physical just by experiencing them; I can’t just inspect them and find the answer to this question. I can inspect an object to find out whether it exemplifies the universal whiteness, but I can’t inspect the universal to find out if it exists in Plato’s heaven. Philosophy does not proceed by inspecting ordinary objects and reporting on their properties: we can’t tell whether they have this or that nature by examining them. We can’t just have a look and see. But these are objects that can be looked at and seen (or known about in some other way such as introspection or intellectual intuition). Nor can we take a closer look at them or take them apart or weigh them in order to answer philosophical questions.  We have to approach the matter indirectly (as we feel like saying) by constructing elaborate and contestable arguments. Maybe these arguments will reveal the truth, and maybe they won’t, but it is clear that we can’t bypass them and just do some ordinary inspecting and telling. We don’t have the faculties for that.
Thus our situation resembles that of the strangely ignorant tribe: they can’t tell what is true either when it comes to ordinary familiar things. They can’t examine or inspect dogs and cats to determine whether they are both animals, or have a look at mountains to see whether they are convex or concave, or check out the human body to see what shape it has. And these are not stupid people, ignorant of everything, understanding nothing; they know many things perfectly well. They just have a strange selective ignorance about quite ordinary things (it isn’t at all like the ignorance of the microscopic world that once afflicted humans). Evidently something about their brains (in concert with that river) explains this odd epistemic deficit; and evidently much the same must be true of us—our brains also prevent us from directly grasping the “philosophical” nature of ordinary things. We don’t know what this something is—it could even be the fact that our brains are made of carbon or are spatial objects—but presumably our philosophical ignorance reflects some truth about our organ of cognition. It may or may not be remediable, but in any case epistemic limits have neurological foundations (even if that just means being very far from the object of interest, as with remote galaxies). But the main point I want to make is that we, like the tribe, suffer from a type of strange ignorance syndrome: we are ignorant of fundamental properties of objects that we interact with daily. 
Isn’t this fact the basis of the philosophical impulse in humans? You find yourself gazing at an object, say a table, noting its various features, and then you start to wonder whether the table is just the sum of its properties, or whether it is really just in your mind, or whether it exists through time (but what is time?). You realize that no amount of gazing is going to answer these questions and you think, “Strange—how come I can’t tell whether the table is one kind of thing rather than another when I can tell its color and shape?”  Then you have a further philosophical thought: Is it even possible for anyone to tell whether the table is one thing or the other? Isn’t it a necessary truth that no one could answer these questions by direct inspection? But what kind of truth is that, and why is the world like that? You have discovered philosophical questions—just by realizing that ordinary things don’t yield up their full nature to your ordinary powers of detection. You have discovered a strange area of ignorance in your view of the world. Members of our tribe might also be aware of their epistemic strangeness: they note that some subject matters yield their truths by ordinary inspection but others don’t—arguments have to be given for why mountains are convex or people tetrapod. It isn’t that they think these questions are philosophy (they may have a sophisticated understanding of philosophical questions possibly superior to ours); they just recognize that they have peculiar pockets of ignorance that they struggle to fill. We too are dimly aware that the familiar world presents us with questions that can’t be answered simply by exercising our powers of direct inspection and ascertaining what is the case. We can’t use the same epistemic powers to answer these questions that we use to answer other questions about the very same objects—such as perception, memory, introspection, and intellectual intuition. It would be nice if we could—if we could just tell by looking whether the will is free, or consciousness is material, or universals are mind-independent abstract entities—but we are not built that way. Empiricism is in effect the wish that this were so (as is rationalism in its fashion), but in reality philosophy must consist in arguing not detecting, persuading not ascertaining. We can’t go on an expedition to find out whether objects are bundles of qualities or whether numbers exist, hoping thereby to detect what is in fact the case. The objects are right under our noses, but our ordinary powers of inspection fail to give us the knowledge we seek: our ignorance is anomalous, singular, peculiar. It is really very strange that we don’t know these things (itself a philosophical thought)—one might even say, astonishing and marvelous. How amazing that we don’t know these basic facts about the things of the world! How, for example, can we be so ignorant of the nature of time, given that we are obsessed with it, experience it daily, and use it to govern our lives? You would think we should know allabout time! Why is there even such a subject as the philosophy of time—there is no subject of the philosophy of water or air or blood? Isn’t it curious that we exhibit this kind of selective ignorance—just as it is curious that our tribe has its areas of selective ignorance? Shouldn’t all knowledge be homogeneous, given that reality is homogeneous (a totality of facts)? Why this odd epistemic partition when there is no ontological partition? Can it be that the world consists of two types of fact—the philosophical facts and non-philosophical facts? But what would that even mean? It is really very peculiar that philosophy exists at all. Yet it does, indisputably so: not all questions about reality can be resolved using our faculties of inspection, detection, and telling. Isn’t it actually quite remarkable that we can’t tell what consciousness is—or causality, moral value, meaning, necessity, the will, generality, etc.? The very existence of philosophy is a puzzling and peculiar thing, by no means predictable from the objective world or our basic epistemic faculties. It really ought not to exist—yet here it is right in front of us. Other terrestrial creatures go about their business inspecting and detecting, never suspecting the existence of philosophical questions; we alone ask questions that transcend our creaturely epistemic faculties—real difficult questions about real things with real natures. We alone know that there is more to reality than our powers of inspection and detection can reveal, and that “philosophy” is the name of this area of study. Strange, surpassing strange. 
 We can inspect the whole physical universe and ascertain facts about it that remove deep ignorance, such as the existence of background radiation. But there is nothing comparable for philosophy: there is no analogue of background radiation that might be detected and provide a demonstration of a particular philosophical position. It couldn’t be that the existence of platonic universals, say, can be established by observing a telltale remnant of their earliest existence in the shape of traces of Form-like activity in space. So even cosmology provides no model for the epistemology of philosophy, despite its speculative character.
 The case of meaning is instructive: we know a lot about meaning and about language in general—what words and sentences mean, that one meaning is different from another, the various categories of meaning—but we don’t know what meaning is. That is, there is no consensus about what is the correct theory of meaning (even within an individual: compare Wittgenstein’s earlier and later theories). We mean things all the time but we can’t tell what constitutes meaning—we can’t inspect it and report our findings. We are strangely ignorant about the nature of meaning. Yet we are not similarly ignorant of phonetics and grammar; our ignorance is curiously localized.
 Note that the same distinction applies to our knowledge of numbers: we can tell by inspection that 4 is even and precedes 5 but we can’t tell by inspection whether it is a platonic entity or exists in the mind or is reducible to marks on paper. Similarly for moral value: we can tell that someone did something wrong by finding out the facts but we can’t tell whether moral values are objective or subjective in this way. The concepts of inspection, detection, and telling apply to the non-perceptual world as well as the perceptual world—and they likewise fail to extend to questions of a philosophical nature. (The point has nothing to do with the question of whether philosophy is an a priori discipline.)
 How did philosophy evolve? What kind of mutation led to it? Would Neanderthals have indulged in it if they had survived? What if dogs underwent a mutation that led to possessing a philosophical brain (and accompanying language)? It seems like an odd adaptation, and quite an abrupt one (a notable saltation). It doesn’t seem to be an inevitable accompaniment of science, since science works by powers of inspection and detection (suitable extended). Nor does it look like an inevitable by-product of the human capacity to argue. Philosophy is a sui generistrait, unique to Homo sapiens, and having no apparent function (even as an offshoot)—its biology is obscure. Somehow we came to be philosophical animals, but we were not vouchsafed any method for detecting the answer to philosophical questions.