Phenomenology of A Priori Knowledge
What is it like to know something a priori? How is it subjectively to know (say) that nothing can both be and not be, or that 2 + 2 = 4? The traditional definition of a posteriori knowledge has it that such knowledge is “dependent on experience”, while a priori knowledge is knowledge that is not dependent on experience. But what is it to know something “by experience”? What properties of experience are relevant to determining the status of an item of knowledge as a posteriori? And how do these properties affect the phenomenology? Evidently an experience is a conscious state, so we would expect that the phenomenology of consciousness would play a role, i.e. what an experience is qua conscious state. It is a specific type of conscious state—the type associated with the operation of the senses. We might then suppose that subjectivity is important: the property of being graspable only from a specific point of view. Then we could say that a posteriori knowledge is knowledge based on evidence that can only be grasped from a specific point of view, i.e. subjective evidence. By contrast a priori knowledge is not based on such subjective evidence—perhaps it is based on objective evidence, i.e. the kind that can be grasped from any point of view. That is certainly an interesting way to formulate the distinction, though it seems rather theory-laden as a criterion of the a priori. Experience is subjective in this sense, but being so seems irrelevant to the distinction in question; and it isn’t clear how it affects the phenomenology of the two types of knowledge. Is it that a posterioriknowledge can only be grasped by someone who shares the type of experience in question, while a prioriknowledge can be grasped irrespective of sharing experience types? But how does that affect what it is like to be the subject of the two types of knowledge? How does the phenomenology differ? Alternatively, we might interpret “experience” to mean “as a result of past experience”, where we use the notion of what has been learned in the past. Then the idea will be that a posteriori knowledge is knowledge acquired by evidence gathered in the past and now stored in memory, while a priori knowledge is not so acquired—it doesn’t rely on “past experience”. This has nothing to do with subjectivity and points of view, and it is a perfectly acceptable use of the word “experience” (“I’ve had a lot experience bird watching”). But it is silent on the question of phenomenology: it says nothing about how it seems to the subject to have the two types of knowledge. Maybe it has implications for phenomenology, but it isn’t a phenomenological description. So is it that there is no phenomenological distinction here—no difference of seeming? Is it that the subject cannot tell the difference between the two sorts of knowledge by means of introspective awareness? There is no phenomenological divide between knowing something a priori and knowing something a posteriori—though there is indeed a distinction between the two types of knowledge. Does the traditional epistemic distinction have a phenomenological counterpart?
We do better to change tack and consider intentionality. One of the characteristics of experience is that it has intentionality—experiences have objects (not necessarily existent). When a subject acquires a piece of a posterioriknowledge she has an experience of an object, as it might be a bird she is seeing. But, it may be thought, a prioriknowledge, not being experience-based, has no such object—it is objectless. This would certainly be reflected in the phenomenology: in one case experience of an object, in the other no experience of an object, because no objectat all. Intuitively, one acquires empirical knowledge by experiencing objects, but rational knowledge does not involve experiencing any object—it comes from “pure reason”. This differentia seems to fit paradigm cases of a priori knowledge quite nicely: our logical knowledge is not based on any apprehension of objects but (as we obscurely say) arises from our grasp of concepts; and our knowledge of analytic truths comes from senses not references. There is nothing like seeing a bird involved, because there is nothing experiential that is involved—and hence no experienced object. Thus a priori knowledge is objectless knowledge, and this is a phenomenological fact about it. It has a distinctive type of intentionality—involving concepts not objects, to put it simply. Alternatively, we could say that a priori knowledge is directed to universals while a posteriori knowledge is directed to particulars: abstract not concrete, general not specific.
But this suggestion runs into a problem with mathematical knowledge. According to Platonism, numbers are objects, so isn’t knowledge of mathematics a posteriori according to the suggestion that an intentionality of objects is necessary and sufficient to make something a case of the a posteriori? Other metaphysical theories of mathematics would not have this consequence—formalism, fictionalism, logicism, maybe intuitionism—but shouldn’t mathematics be a priori even under Platonism? Actually that is not so obvious on reflection: suppose cosmologists discover a peculiar kind of light matter in a remote section of the universe that gives off a faint kind of energy that is perceptible by the human nervous system—and this is associated with mathematical knowledge. Wouldn’t we then say that it has turned out that mathematical knowledge is a posteriori? There is a type of experience of mathematical objects, barely perceptible, that gives rise to mathematical knowledge, thus rendering it a posteriori. But there is also this question: even if there are mathematical objects, are they part of the phenomenology of mathematics? That is far from clear: does it seem to us that Platonism is true? Is that a datum of consciousness? And what notion of object is in play here? It is certainly not the notion of material particulars in space, or even mental particulars in non-space. We don’t feel ourselves confronted by numbers, as we feel confronted by physical objects—faced with them, assailed by them. To call numbers objects seems like a stretch, precisely because that is not true to the phenomenology: it doesn’t seem to us that numbers are at a certain distance from us and each other, or that there is perceptual constancy with respect to our perception of numbers, or that there is a type-token distinction for numbers. Talk of objects here feels theoretical and tendentious not natural and intuitive. Nor does anyone ever argue that Platonism must be true because numbers seem like objects. Nor is it that our mathematical knowledge is produced by anything deserving the name of experience, so we don’t have it as a result of experiences of objects. So we can reasonably say that mathematical knowledge is not object-directed from a phenomenological point of view; it is nothing like our knowledge of material things in this respect (this is why non-Platonist theories don’t immediately strike us as false to our lived experience with mathematics). It is true that mathematical knowledge is problematic—notoriously, it isn’t causally explicable—but it is not obligatory to describe it as phenomenologically object-directed. And even if it were, we could always amend our criterion to say that a priori knowledge is not based on experience of particulars—concrete spatiotemporal entities—but rather on the apprehension of abstract entities (non-particulars).
There is a further fact about sensory experience that distinguishes the a priori from the a posteriori, namely the role of the sense organs. It is part of the phenomenology of empirical knowledge that we are aware of our sense organs, and hence our body. I know, for example, that my current experience of a bird is visual and that my eyes are involved in having such experience. When acquiring knowledge empirically I am aware that my senses are operating in a certain way—my eyes and head are moving, for instance. This is a part of the phenomenology—not just external objects of experience but also the object that is my body, specifically the physical sense organs. But in the case of a priori knowledge there is no such awareness of my body—I am not aware of a bodily sense organ responsible for picking up information about the objects of my a priori knowledge. I am not aware of a part of my body vouchsafing to me mathematical knowledge, say. Of course, the brain is involved in having such knowledge, but the brain is not a phenomenological component of acquiring that knowledge—there is no bodily sense organ geared to the mathematical world. So there is a double independence from objects: no external object of awareness, and no bodily object producing awareness. In gaining empirical knowledge I have awareness of external objects and I also have awareness of my own body as a mediator of knowledge, but neither is true of a priori knowledge. In this sense the phenomenology of a priori knowledge is disembodied as well as objectless.
I would describe a priori knowledge as phenomenologically empty: it is not experiential or object-directed or body involving. By contrast a posteriori knowledge is full: replete with objects and the body and subjective experience. Sartre might say that the former is a phenomenology of Nothingness while the latter is a phenomenology of Being. Of course, a priori knowledge has intentional objects—concepts, universals, abstract entities—but these don’t saturate consciousness in the way the components of a posteriori knowledge do. I am now aware of my visual experience, its concrete objects, and the body that enables me to have experience of objects: but I am not likewise aware of such things when I think about logic or numbers or analytic propositions—I am simply aware of certain truths. I am aware of the apparatus of knowledge in the former case, but not in the latter. Thus a priori knowledge seems more mysterious to me, because I can’t apprehend its machinery—what makes it possible. From a phenomenological point of view, it seems like a deliverance from on high—a kind of miracle. I can know that 2 + 2 = 4! How I know this, I don’t know—but I can know what makes my knowledge of my immediate environment possible, viz. experience, perceived objects, and my sense organs. This is the phenomenological upshot of the traditional way of marking the distinction between the a priori and the a posteriori: it arises from the nature of sense experience as a phenomenological category. The phenomenology of a posteriori knowledge is the phenomenology of experience as object-directed and body-mediated; the phenomenology of a priori knowledge is absent these components, presenting itself rather as objectless and disembodied. The body and the perceived world are phenomenologically irrelevant to the etiology of a priori knowledge. It appears to transcend such things.
 Of course, both sorts of knowledge have objects—either concepts or objects—it is just that concepts are not objects. This is the familiar ambiguity of “object” as between a type of entity and being a target of a mental state (an “object of thought”).
 I am not saying it does transcend the world of material particulars—we need a body and brain to have a prioriknowledge—but as a matter of phenomenology these things don’t enter the picture. Hence a priori knowledge has a curious thinness and impalpability. It is characterized by absence—what is not suffused by experience, objects, and the body.