The philosophical notion proper of the a priori lacks a prominent professional anthropological genealogy. Nevertheless, it should serve well here to give my anthropological ideas philosophical expression. Although it is a Scholastic term that emerged from certain ideas of Aristotle, in recent centuries it is most critically associated with the thought of Kant and his ‘Copernican revolution’, in which he denied the obvious: not, as Copernicus had already done, that the universe has the earth as its center, but, in a limited yet deep sense restoring to humans the centrality of place of which Copernicus had deprived them, that the world, as we find it, stands utterly outside of our experience of it.1
The term ‘a priori’ literally translates as ‘from what is prior’, as opposed to a posteriori or ‘from what is posterior’. Initially, the terms related directly to the idea of causality, since to know something from what comes before it is to know it by its cause. For Kant, however, who was concerned with the conditions of knowing, the term had to do with whether one's knowledge was based on experience or not. For to know something from what comes after the fact is to know it inductively, from the facts themselves. The critical Kantian distinction, then, obtained between a posteriori truths, or knowledge derived empirically, and a priori truths, or knowledge derived otherwise.
Obviously, at least in Western thought, insofar as it is defined as non-empirical, a priori knowledge appears to be a question of reason in Hume's sense of the relations of ideas. As such, it would seem to be logically necessary and universal, in contrast to a posteriori knowledge, which is contingent or relative and particular. For Kant, however, who was chiefly concerned to put metaphysical knowledge on a sound footing, it could not do to reduce the a priori thus to a matter of ordinary reason. He saw that humans cannot help making important and far-reaching judgments that present themselves as necessarily and universally true but are nevertheless not simply a matter of formal logical connection.
Judgments based on a relation of identity between subject and predicate, in which it would be self-contradictory to deny the truth of the predicate (as in, say, ‘all bodies are extended’), Kant called analytic; judgments that do not enjoy this sheer logical independence, but are, instead, matters of fact, he spoke of as synthetic. Kant observed, however, that there are critical judgments that cut across the usual classifications, amounting to knowledge that is neither exactly learned by experience nor derived from formal logic as such, knowledge that is, as he said, both a priori and synthetic. The privileged philosophical site of such judgments is the Meno, in which Plato takes up the problem of how it is possible to inquire into the nature of something if one does not know what it is. In response to this problem, Plato has Socrates argue (to Meno) that because the soul is immortal and has had a previous existence, it recalls what it had learned before; arithmetic and geometry are given as examples of such knowledge. Kant, too, draws on these examples, arguing that the truths of mathematics and geometry—for example, the sum of the angles of any triangle is 180 degrees—are, although neither given in the concept of a triangle nor produced simply on the basis of knowing, a priori or universally necessary. But in addressing the question of how we come to have such synthetic a priori knowledge, even though he invokes a sense of prior knowledge from experience, Kant departs from the Platonic belief in rebirth and from Platonic metaphysics, since the latter's idealism posits a supersensible reality without regard to the subject's point of view. For Kant, the connection between the concept of a triangle and the truths about its angles consists in intuitive forms and transcendental logic. That is, he found his answer in pure reason, the reason of necessary and universal categories rather than the reason of particular ideas. Acknowledging that any world presupposes a subjective point of view, he sought to determine the logical conditions of the very possibility of a point a view and of experiential knowledge. Consequently, while Kant tended to exemplify synthetic a priori knowledge by referring to arithmetic and geometry, natural science, and metaphysics, following his conception of transcendental logic, most if not all of our most fundamental understandings about the world must ultimately be keyed to knowledge of this kind.
As knowledge that lies somehow between apparently mutually exclusive onto-epistemological categories, Kant's synthetic a priori plainly turns in the direction of nondualism. Such a turning is implicit in his revolutionary understanding that far from being wholly independent of us, the external world conforms to the categorical structures of mind, or, in other words, that that world is given form by us. Nevertheless, for all its revolutionary force, Kant's synthetic a priori not only falls short of nondualism, but also managed to put dualism on a more sophisticated intellectual footing than had previously been the case. Although he aims to critique reason, his deductive appeal to transcendental logic rather than to experience (in this word's dynamic sense of ‘practice’) leaves reason, in the last instance, in command.
Kant argued that although synthetic a priori truths are not analytically—and thus tautologically—necessary, they must be the case if human life is to be thinkable. In other words, asking himself what are the conceptual categories necessary to conceive of the human world, he deduced certain constituting concepts. Thus, he found that although spatio-temporal concepts such as, for example, ‘object’ and ‘cause’ are neither, strictly speaking, analytic nor empirically learned, they are presupposed in all human experience. As such, they and their like are necessary and universal, presenting themselves as the categorical begetters of human existence.
Plainly, Kant's notion of the synthetic a priori runs contrary to Hume's skepticism, according to which our knowledge of the external world can never really be rationally justified. Hume's skepticism followed naturally from his coupling of radical empiricism with ontological dualism, a combination that guarantees that what we know by experience to be the case can be established psychologically but not logically. Nevertheless, Kant's notion served in at least two crucial ways to reinforce rather than refute ontological dualism. One way concerns the fact that Kant, in an important sense, and despite his anti-Cartesianism, embraced the Cartesian cogito or ‘I think’ (Heidegger 1978: 45, 367). In Kant's argument, the self is rendered as, although emphatically not, as in Descartes’ discourse, a ‘thinking stuff’ or substance, certainly timeless—something akin to a transcendental ego. “There can be in us,” Kant writes (quoted in Walsh 1967: 312),
no items of knowledge…without that unity of consciousness which precedes all data of intuitions, and by relation to which representation of objects is alone possible. This pure original unchangeable consciousness I shall name transcendental apperception…[U]nity of consciousness would be impossible if the mind in knowledge of the manifold could not become conscious of the identity of function whereby it synthetically combines it in one knowledge. The original and necessary consciousness of the identity of the self is thus at the same time a consciousness of an equally necessary unity of the synthesis of all appearances according to concepts, that is, according to rules.
In other words, subjectivity is still presented by Kant as ontologically utterly distinct from the objective world. Indeed, for Kant, the subject is not part of the ‘real’ world. Instead, it obtains in the transcendental logic (the realm of the ideal) that makes it possible to experience a world at all. To be sure, Kant's depiction of consciousness as active rather than passive serves, in a significant way, to link the subject to the object. But that dialectical linkage is predicated on a logically formal and complete distinction between form and content, by virtue of which what we give to the world is not empirical substance but shape alone. (“The identification of the a priori with the formal is the fundamental error of Kant,” observed Scheler [cited in Dufrenne 1966: 57].) As a consequence,