Chapter Eight Is There a Priori Knowledge? For advocates of a priori knowledge, the chief task is to explain how such knowledge comes about. According to Laurence BonJour, we acquire a priori knowledge of a proposition p when we grasp that p is necessarily true. For opponents, the task is twofold. They must give an account of how empirical knowledge of putative a priori propositions is possible, and they must explain why such propositions cannot be known in the way BonJour claims, namely through rational insight or the recognition of necessity. To do the former, Michael Devitt appeals to the thesis of holism, according to which beliefs face the tribunal of experience not individually but only as a system. Putative a priori propositions are part of our belief system and thus, like everything else we believe, are subject to revision in the light of experience. To accomplish the second task, Devitt argues that, unlike the empirical justification provided by experi- ences, rational insight as a source of knowledge is utterly obscure. In response, BonJour claims that the appeal to holism begs the question because it leaves unanswered the question of which aspects of a holistic system are indicative of truth, and that empirical justification, at least when it comes to indirect empirical knowledge, is no less prob- lematic than a priori justification. In the final round of their exchange, Devitt denies and BonJour asserts (i) that justification through holistic evidence requires knowing that such evidence is truth indicative, (ii) that holistic naturalism is inflicted with circularity, and (iii) that BonJour’s rational insight account of a priori knowledge avoids circularity. In Defense of the a Priori Laurence BonJour The official subject of this debate is the existence of a priori knowledge. But the main focus of my discussion will in fact be not a priori knowledge, but a priori Contemporary Debates in Epistemology, Second Edition. Edited by Matthias Steup, John Turri, and Ernest Sosa. © 2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc. justification – or rather, more specifically, a priori reasons for believing something to be true. In approaching the issue in this way, I am assuming both (i) that justifi- cation is one of the requirements for knowledge (the only one to which the issue of a priori status is relevant) and (ii) that justification in the relevant sense consists in having a good reason for thinking that the belief in question is true. But having stated these two background assumptions, I will say nothing further in support of them here. The view I will defend is that a priori reasons, in a sense yet to be clarified, do exist (and in consequence that a version of epistemological rationalism is true). But the idea of an a priori reason (and also the associated rationalist view) has been understood in a number of different ways, and I will not be defending all of the specific claims that have been associated with this sort of position. My aim is to defend what I take to be a relatively minimal version of the idea of an a priori reason (and of rationalism): more or less the most minimal version that is both philosophically interesting and reason- ably faithful to the historical dialectic. All this will take some explanation. The Nature of a Priori Reasons As I will understand it here, the concept of an a priori reason has two basic elements, one negative and one positive, the negative one initially more obvious, but both in the end equally essential. Negatively, an a priori reason for thinking that a claim is true is one whose rational force or cogency does not derive from experience, either directly (as in sense perception) or indirectly (as by inference of any sort – deductive, induc- tive, or explanatory – whose premises derive their acceptability from experience). That such a reason is in this way independent of experience does not mean that someone who has undergone no experience of any sort could be in possession of it, since the possession of an a priori reason requires understanding the claim for which it is a reason, and experience, even experience of some fairly specific sort, might be required for that. Nor does the idea of an a priori reason, when understood in this way, imply either: (i) that experiences of some sort could not also count for or against the claim in question; or (ii) that such experiences could not override, perhaps even more or less conclusively, the a priori reason in question; or still less (iii) that an a priori reason renders the claim certain or infallible. All of these further claims might be true in some cases (though not, I believe, in all or even most), but they in no way follow from or are essential to the basic idea of an a priori reason itself. What then counts, for these purposes, as experience? Obviously the paradigm cases are the various sorts of sense experience, including such things as kinesthetic experi- ences of bodily orientation in addition to those deriving from the five standard senses. But, in opposition to a number of recent discussions, I would argue that introspective awareness of one’s thoughts, sensations, and other mental states should also count as a variety of experience, and the reasons for belief that such experience provides as empirical rather than a priori. Introspective experience may not depend on clearly identifiable sense organs, but it is still pretty clearly an awareness of temporally located contingent facts that depends on causal relations between those specific facts and the correlative state of awareness; it is thus far more analogous to sense experience than it is to the sort of experiential process, if it should even be called that, that is involved 178 Laurence BonJour in the most paradigmatic cases of allegedly a priori reasons. And basically the same thing is true of even the reason for belief in one’s own existence that is supplied by the Cartesian cogito, since this is based on introspective awareness of the occurrence of specific thoughts and sensations. Turning to the positive aspect of the concept of an a priori reason, the traditional view, which I believe to be essentially correct, is that in the most basic cases such rea- sons result from direct or immediate insight into the truth, indeed the necessary truth, of the relevant claim. (A derivative class of a priori reasons, about which little will be said here, results from similar insights into the derivability of a claim from one or more premises for which such a priori reasons exist or from a chain of such derivations. And a partially a priori reason may result from an a priori insight into the derivability of a claim from others established on broadly empirical grounds.) Though the term “intui- tion” has often been used to refer to such insights, I will refer to them simply as “a priori insights,” thus, I hope, avoiding any confusion with the other uses of the rather slippery term “intuition.” Here it is important to be clear at the outset that insights of this sort are not sup- posed to be merely brute convictions of truth, on a par with the hunches and fears that may simply strike someone in a psychologically compelling way. On the contrary, a priori insights at least purport to reveal not just that the claim is or must be true but also, at some level, why this is and indeed must be so. They are thus putative insights into the essential nature of things or situations of the relevant kind, into the way that reality in the respect in question must be. One other point about the nature of a priori insights should also be briefly men- tioned. For a variety of reasons, but most fundamentally because of the role that such insights are supposed to play in deductive inference, it is often and quite possibly always a mistake to construe them as propositional in form. The problem here is essen- tially the one pointed out long ago by Lewis Carroll: at least in the most fundamental sorts of cases (think here of modus ponens), the application of a propositional insight concerning the cogency of such an inference would require either a further inference of the very sort in question or one equally fundamental, thereby leading to a vicious regress. Instead, I suggest, the relevant logical insight must be construed as non-prop- ositional in character, as a direct grasping of the way in which the conclusion is related to the premises and validly flows from them. And once the need for this non-proposi- tional conception of a priori insight is appreciated in the context of deductive inference, it seems to me in fact plausible to extend it to many other cases as well; in particular, it seems plausible to regard the most fundamental insights pertaining to each of the examples listed in the following section as non-propositional in character.1 The Argument from Examples for the Existence of a Priori Reasons Why then should it be thought that reasons having this a priori character genuinely exist? One reason is that there seem to be many, many examples of propositions for which there are clear and obvious reasons of this sort. Here the most obvious examples come from mathematics and logic, but there are others of many widely varying kinds. In Defense of the a Priori 179 For present purposes, a misleadingly short list, reflecting some of the main types, will have to do: (1) 2 + 3 = 5. (2) All cubes have 12 edges.