I argue that you can have a priori knowledge of propositions that neither are nor appear necessarily true. You can know a priori contingent propositions that you recognize as such. This overturns a standard view in contemporary epistemology and the traditional view of the a priori, which restrict a priori knowledge to necessary truths, or at least to truths that appear necessary.

The distinction between a priori and a posteriori knowledge has been the subject of an enormous amount of discussion, but the literature is biased against recognizing the intimate relationship between these forms of knowledge. For instance, it seems to be almost impossible to find a sample of pure a priori or a posteriori knowledge. In this paper, it will be suggested that distinguishing between a priori and a posteriori is more problematic than is often suggested, and that (...) a priori and a posteriori resources are in fact used in parallel. We will define this relationship between a priori and a posteriori knowledge as the bootstrapping relationship. As we will see, this relationship gives us reasons to seek for an altogether novel definition of a priori and a posteriori knowledge. Specifically, we will have to analyse the relationship between a priori knowledge and a priori reasoning , and it will be suggested that the latter serves as a more promising starting point for the analysis of aprioricity. We will also analyse a number of examples from the natural sciences and consider the role of a priori reasoning in these examples. The focus of this paper is the analysis of the concepts of a priori and a posteriori knowledge rather than the epistemic domain of a posteriori and a priori justification. (shrink)

In his recent book Constructing the World, David Chalmers defends A Priori Scrutability, the thesis that there is a compact class of truths such that for any truth p, a Laplacian intellect could know a priori that if the truths in that class hold, then p. In this paper, I develop an objection to Chalmers’ thesis that focuses on his treatment of a so-called that’s-all truth. My objection draws on Theodore Sider’s discussion of border-sensitive properties, and also on (...) the causal phenomenon of double prevention. (shrink)

The idea that the epistemology of modality is in some sense a priori is a popular one, but it has turned out to be difficult to precisify in a way that does not expose it to decisive counterexamples. The most common precisifications follow Kripke’s suggestion that cases of necessary a posteriori truth that can be known a priori to be necessary if true ‘may give a clue to a general characterization of a posteriori knowledge of necessary truths’. The (...) idea is that whether it is contingent whether p can be known a priori for at least some broad range of sentences ‘p’. Recently, Al Casullo and Jens Kipper have discussed restrictions of such principles to atomic sentences. We show that decisive counterexamples even to such dramatically restricted Kripke-style principles can be constructed using minimal logical resources. We then consider further restrictions, and show that the counterexamples to the original principles can be turned into counterexamples to the further restricted principles. We conclude that, if there are any true restrictions of Kripke-style principles, then they are so weak as to be of little epistemological interest. (shrink)

This paper provides a defense of two traditional theses: the Autonomy of Philosophy and the Authority of Philosophy. The first step is a defense of the evidential status of intuitions (intellectual seemings). Rival views (such as radical empiricism), which reject the evidential status of intuitions, are shown to be epistemically self-defeating. It is then argued that the only way to explain the evidential status of intuitions is to invoke modal reliabilism. This theory requires that intuitions have a certain qualified modal (...) tie to the truth. This result is then used as the basis of the defense of the Autonomy and Authority theses. The paper closes with a defense of the two theses against a potential threat from scientific essentialism. (shrink)

This paper argues that a priori justification is, in principle, compatible with naturalism—if the a priori is understood in a way that is free of the inessential properties that, historically, have been associated with the concept. I argue that empirical indefeasibility is essential to the primary notion of the a priori ; however, the indefeasibility requirement should be interpreted in such a way that we can be fallibilist about apriori-justified claims. This fallibilist notion of the a (...) class='Hi'>priori accords with the naturalist’s commitment to scientific methodology in that it allows for apriori-justified claims to be sensitive to further conceptual developments and the expansion of evidence. The fallibilist apriorist allows that an a priori claim is revisable in only a purely epistemic sense. This modal claim is weaker than what is required for a revisability thesis to establish empiricism, so fallibilist apriorism represents a distinct position. (shrink)

The topic of a priori knowledge is approached through the theory of evidence. A shortcoming in traditional formulations of moderate rationalism and moderate empiricism is that they fail to explain why rational intuition and phenomenal experience count as basic sources of evidence. This explanatory gap is filled by modal reliabilism -- the theory that there is a qualified modal tie between basic sources of evidence and the truth. This tie to the truth is then explained by the theory of (...) concept possession: this tie is a consequence of what, by definition, it is to possess (i.e., to understand) one’s concepts. A corollary of the overall account is that the a priori disciplines (logic, mathematics, philosophy) can be largely autonomous from the empirical sciences. (shrink)

This is the second in a two part series of articles that attempt to clarify the nature and enduring relevance of Kant's concept of a priori knowledge. (For Part I, see below.) In this article I focus mainly on Saul Kripke's critique of Kant, in Naming and Necessity. I argue that Kripke draws attention to a genuine defect in Kant's epistemological framework, but that he used definitions of certain key terms that were quite different from Kant's definitions. When Kripke's (...) definitions are replaced by Kant's definitions, Kripke's account of the status of naming turns out to be a defense of analytic aposteriority as a significant classification of knowledge that Kant neglected. I also introduce here a new way of understanding such epistemological labels, as defining the perspective adopted by the knowing subject in a given situation, rather than an objective characteristic of certain propositions as such. (shrink)

In this paper I will offer a novel understanding of a priori knowledge. My claim is that the sharp distinction that is usually made between a priori and a posteriori knowledge is groundless. It will be argued that a plausible understanding of a priori and a posteriori knowledge has to acknowledge that they are in a constant bootstrapping relationship. It is also crucial that we distinguish between a priori propositions that hold in the actual world and (...) merely possible, non-actual a priori propositions, as we will see when considering cases like Euclidean geometry. Furthermore, contrary to what Kripke seems to suggest, a priori knowledge is intimately connected with metaphysical modality, indeed, grounded in it. The task of a priori reasoning, according to this account, is to delimit the space of metaphysically possible worlds in order for us to be able to determine what is actual. (shrink)

This paper contains replies to comments on the author's paper "A Priori Knowledge and the Scope of Philosophy." Several points in the argument of that paper are given further clarification: the notion of our standard justificatory procedure, the notion of a basic source of evidence, and the doctrine of modal reliabilism. The reliability of intuition is then defended against Lycan's skepticism and a response is given to Lycan's claim that the scope of a priori knowledge does not include (...) philosophically central topics such as the nature of consciousness. Next a counterfactual account of intuitions proposed by Sosa is criticized. Finally, in response to certain questions raised by Sosa, the explanation of the evidential status of intuition offered in the original paper receives further elaboration. (shrink)

This paper is aimed at understanding one central aspect of Bolzano's views on deductive knowledge: what it means for a proposition and for a term to be known a priori. I argue that, for Bolzano, a priori knowledge is knowledge by virtue of meaning and that Bolzano has substantial views about meaning and what it is to know the latter. In particular, Bolzano believes that meaning is determined by implicit definition, i.e. the fundamental propositions in a deductive system. (...) I go into some detail in presenting and discussing Bolzano's views on grounding, a priori knowledge and implicit definition. I explain why other aspects of Bolzano's theory and, in particular, his peculiar understanding of analyticity and the related notion of Ableitbarkeit might, as it has invariably in the past, mislead one to believe that Bolzano lacks a significant account oï a priori knowledge. Throughout the paper, I point out to the ways in which, in this respect, Bolzano's antagonistic relationship to Kant directly shaped his own views. (shrink)

In this paper I argue for a priori conjectural scientific knowledge about the world. Physics persistently only accepts unified theories, even though endlessly many empirically more successful disunified rivals are always available. This persistent preference for unified theories, against empirical considerations, means that physics makes a substantial, persistent metaphysical assumption, to the effect that the universe has a (more or less) unified dynamic structure. In order to clarify what this assumption amounts to, I solve the problem of what it (...) means to say of a theory that it is unified. There are, I argue, eight different kinds of unity important in theoretical physics, all varieties of one basic idea. This provides us with a precise way of partially ordering physical theories with respect to their degree of unity. It also leads to a hierarchical view of physics, according to which physics makes a number of increasingly insubstantial metaphysical assumptions concerning the comprehensibility and knowability of the universe. Two of these are identified as constituting a priori conjectures. I conclude by arguing that the view developed in the paper resolves the traditional clash between empiricism and rationalism in the philosophy of science, and has important implications for science, and for academic inquiry more generally. (shrink)

We consider a natural-language sentence that cannot be formally represented in a first-order language for epistemic two-dimensional semantics. We also prove this claim in the “Appendix” section. It turns out, however, that the most natural ways to repair the expressive inadequacy of the first-order language render moot the original philosophical motivation of formalizing a priori knowability as necessity along the diagonal.

(2014). A Priori Conditionals and the Conceivability of Zombies. Philosophical Papers: Vol. 43, No. 2, pp. 227-253.

The distinction between a priori knowledge and a posteriori knowledge has come under attack in the recent literature by Philip Kitcher, John Hawthorne, C. S. Jenkins, and Timothy Williamson. Evaluating the attacks requires answering two questions. First, have they hit their target? Second, are they compelling? My goal is to argue that the attacks fail because they miss their target. Since the attacks are directed at a particular concept or distinction, they must accurately locate the target concept or distinction. (...) Accurately locating the target concept or distinction requires correctly articulating that concept or distinction. The attacks miss their target because they fail to correctly articulate the target concept or distinction. I go on to present a different challenge to the a priori-a posteriori distinction. This challenge is not directed at the coherence or significance of the distinction. Its target is the traditional view that all knowledge (or justified belief) is either a priori or a posteriori. (shrink)

In this paper I argue that a priori arguments fail to present any real problem for physicalism. They beg the question against physicalism in the sense that the argument will only seem compelling if one is already assuming that qualitative properties are nonphysical. To show this I will present the reverse-zombie and reverse-knowledge arguments. The only evidence against physicalism is a priori arguments, but there are also a priori arguments against dualism of exactly the same variety. Each (...) of these parity arguments has premises that are just as intuitively plausible, and it cannot be the case that both the traditional scenarios and the reverse-scenarios are all ideally conceivable. Given this one set must be merely prima facie conceivable and only empirical methods will tell us which is which. So, by the time a priori methodology will be of any use it will be too late. (shrink)

This paper examines popular‘conventionalist’explanations of why philosophers need not back up their claims about how‘we’use our words with empirical studies of actual usage. It argues that such explanations are incompatible with a number of currently popular and plausible assumptions about language's ‘social’character. Alternate explanations of the philosopher's purported entitlement to make a priori claims about‘our’usage are then suggested. While these alternate explanations would, unlike the conventionalist ones, be compatible with the more social picture of language, they are each shown (...) to face serious problems of their own. (shrink)

This paper argues for and explores the implications of the following epistemological principle for knowability a priori (with 'Ka' abbreviating 'it is knowable a priori that'). -/- (AK) For all ϕ, ψ such that ϕ semantically presupposes ψ: if Ka(ϕ), Ka(ψ). -/- Well-known arguments for the contingent a priori and a priori knowledge of logical truth founder when the semantic presuppositions of the putative items of knowledge are made explicit. Likewise, certain kinds of analytic truth turn (...) out to carry semantic presuppositions that make them ineligible as items of a priori knowledge. -/- On a happier note, I argue that (AK) offers an appealing, theory-neutral explanation of the a posteriori character of certain necessary identities, as well as an interesting rationalization for a commonplace linguistic maneuver in philosophical work on the a priori. (shrink)

I defend the claim that physicalism is not committed to the view that non-phenomenal macrophysical truths are a priori entailed by the conjunction of microphysical truths , basic indexical facts , and a 'that's all' claim . I do so by showing that Chalmers and Jackson's most popular and influential argument in support of the claim that PIT ⊃ M is a priori, where 'M' stands for any ordinary, non-phenomenal, macroscopic truth, falls short of establishing its conclusion. My (...) objection to Chalmers and Jackson's argument takes the form of a nested dilemma. Let 'Conceptual Competence Principle ' stand for the following claim: for any complete microphysical description D of a world w, a subject who is in possession of and competent with a macrophysical concept C is capable of determining a priori the extension of C. Either Jackson and Chalmers accept CCP or not. If the latter, then they cannot demonstrate that the conditional PIT ⊃ M is a priori. If the former, then they have a choice: they can either cite reasons that support the principle or argue that the principle should be taken for granted since it is entailed by the very notion of conceptual competence. But both alternatives are problematic. In regard to the first horn of this latter dilemma, I show not only that there are no good reasons to support the principle, but that there are also reasons to reject it. In regard to the second horn, I show that it cannot be the case that CCP is part of the very notion of conceptual competence. The conceptual capacity expressed by CCP requires that certain bridge principles or conditionals, which link the microphysical level to the macroscopic level, are either implicitly or explicitly given to the subject. But, as I argue, Chalmers and Jackson have no way of accounting for these bridge principles or conditionals in a manner that does not trivialize their position. (shrink)

In this paper I argue that Michael Friedman's conception of the contitutive a priori faces two serious problems. These two problems show that the view collapses into a form of conventionalism.

Objective reasons are given by the facts. Subjective reasons are given by one’s perspective on the facts. Subjective reasons, not objective reasons, determine what it is rational to do. In this paper, I argue against a prominent account of subjective reasons. The problem with that account, I suggest, is that it makes what one has subjective reason to do, and hence what it is rational to do, turn on matters outside or independent of one’s perspective. After explaining and establishing this (...) point, I offer a novel account of subjective reasons which avoids the problem. (shrink)

On rationalist infallibilism, a wide range of both (i) analytic and (ii) synthetic a priori propositions can be infallibly justified (or absolutely warranted), i.e., justified to a degree that entails their truth and precludes their falsity. Though rationalist infallibilism is indisputably running its course, adherence to at least one of the two species of infallible a priori justification refuses to disappear from mainstream epistemology. Among others, Putnam (1978) still professes the a priori infallibility of some category (i) (...) propositions, while Burge (1986, 1988, 1996) and Lewis (1996) have recently affirmed the a priori infallibility of some category (ii) propositions. In this paper, I take aim at rationalist infallibilism by calling into question the a priori infallibility of both analytic and synthetic propositions. The upshot will be twofold: first, rationalist infallibilism unsurprisingly emerges as a defective epistemological doctrine, and second, more importantly, the case for the a priori infallibility of one or both categories of propositions turns out to lack cogency. (shrink)

Kripke maintains that one who stipulatively introduces the term ' one meter' as a rigid designator for the length of a certain stick s at time t is in a position to know a priori that if s exists at t then the length of s at t is one meter. Some (e.g., Soames 2003) have objected to this alleged instance of the contingent a priori on the grounds that the stipulator's knowledge would have to be based in (...) part on substantive metalinguistic knowledge. I examine Soames's argument for the a posteriority of the relevant metalinguistic knowledge, and I argue that its main premise is false. (shrink)

I look at incompatibilist arguments aimed at showing that the conjunction of the thesis that a subject has privileged, a priori access to the contents of her own thoughts, on the one hand, and of semantic externalism, on the other, lead to a putatively absurd conclusion, namely, a priori knowledge of the external world. I focus on arguments involving a variety of externalism resulting from the singularity or object-dependence of certain terms such as the demonstrative ‘that’. McKinsey argues (...) that incompatibilist arguments employing such externalist theses are at their strongest, and conclusively show that privileged access must be rejected. While I agree on the truth of the relevant externalist theses, I show that all plausible versions of the incompatibilist reductio argument as applied to such theses are fundamentally flawed, for these versions of the argument must make assumptions that lead to putatively absurd knowledge of the external world independently of the thesis of privileged access. (shrink)

O artigo busca trabalhar um aspecto pouco explorado da argumentação de "História da Loucura": a questão, brevemente enunciada por Foucault, de um "a priori concreto" das ciências "psi". Nisso, serão trabalhadas duas questões principais, a saber: a do estatuto do conhecimento sobre as doenças mentais como tributário de uma demanda moral (não científica), e a do estatuto do médico como "cientista" da loucura. Dentro desses dois âmbitos críticos, o Foucault que escreve seu primeiro grande livro não poupa nem mesmo (...) o lugar do psicanalista. (shrink)

This paper is an examination of the contingent a priori and the necessary a posteriori. In particular, it considers -- and assesses -- the criticisms that Nathan Salmon makes of the views of Saul Kripke.

The topic of this article is the closure of a priori knowability under a priori knowable material implication: if a material conditional is a priori knowable and if the antecedent is a priori knowable, then the consequent is a priori knowable as well. This principle is arguably correct under certain conditions, but there is at least one counterexample when completely unrestricted. To deal with this, Anderson proposes to restrict the closure principle to necessary truths and (...) Horsten suggests to restrict it to formulas that belong to less expressive languages. In this article it is argued that Horsten’s restriction strategy fails, because one can deduce that knowable ignorance entails necessary ignorance from the closure principle and some modest background assumptions, even if the expressive resources do not go beyond those needed to formulate the closure principle itself. It is also argued that it is hard to find a justification for Anderson’s restricted closure principle, because one cannot deduce it even if one assumes very strong modal and epistemic background principles. In addition, there is an independently plausible alternative closure principle that avoids all the problems without the need for restriction. (shrink)

This paper has two parts. In the first I give a brief historical account of the a priori and point out the central and problematic role of 'Erfahrung überhaupt' in Kant’s transcendental philosophy. In the second and main part I offer a criticism of Kripke’s arguments for the contingent a priori and I thereby question his radical separation of metaphysics and epistemology.

Kant's philosophy promises to explain various synthetic a priori claims. Yet, as several of his commentators have noted, it is hard to see how these explanations could work unless they themselves rested on unexplained synthetic a priori claims. Since Kant appears to demand explanations for all synthetic a priori claims, it would seem that his project fails on its own terms. I argue, however, that Kant holds that explanations are required only for synthetic a priori claims (...) about (purportedly) experience-independent entities, and that his project rests on a rationalist method of reflection that justifies certain basic synthetic a priori claims. (shrink)

This article discusses the role of a priori and a posteriori knowledge and methods in metaphysics and metametaphysics. Issues discussed include the viability of the distinction, the continuity of a priori and a posteriori methods, connections to modal epistemology, and the role of the distinction for science and naturalistic metaphysics.

When reasons are given for compositionality, the arguments usually purport to establish compositionality in an almost a priori manner. I will rehearse these arguments why one could think that compositionality is a priori true, or almost a priori true, and will find all of them inconclusive. This, in itself, is no reason against compositionality, but a reason to try to establish or defend the principle on other than quasi-a priori grounds.

The Marburg neo-Kantians argue that Hermann von Helmholtz's empiricist account of the a priori does not account for certain knowledge, since it is based on a psychological phenomenon, trust in the regularities of nature. They argue that Helmholtz's account raises the 'problem of validity' (Gueltigkeitsproblem): how to establish a warranted claim that observed regularities are based on actual relations. I reconstruct Heinrich Hertz's and Ludwig Wittgenstein's Bild theoretic answer to the problem of validity: that scientists and philosophers can depict (...) the necessary a priori constraints on states of affairs in a given system, and can establish whether these relations are actual relations in nature. The analysis of necessity within a system is a lasting contribution of the Bild theory. However, Hertz and Wittgenstein argue that the logical and mathematical sentences of a Bild are rules, tools for constructing relations, and the rules themselves are meaningless outside the theory. Carnap revises the argument for validity by attempting to give semantic rules for translation between frameworks. Russell and Quine object that pragmatics better accounts for the role of a priori reasoning in translating between frameworks. The conclusion of the tale, then, is a partial vindication of Helmholtz's original account. (shrink)

Hillary Putnam has famously argued that we can know that we are not brains in a vat because the hypothesis that we are is self-refuting. While Putnam's argument has generated interest primarily as a novel response to skepticism, his original use of the brain in a vat scenario was meant to illustrate a point about the "mind/world relationship." In particular, he intended it to be part of an argument against the coherence of metaphysical realism, and thus to be part of (...) a defense of his conception of truth as idealized rational acceptability. Putnam's conclusions about the scenario are, however, actually out of line with central and plausible aspects of his own account of the relationship between our minds and the world. Reflections on semantics give us no compelling reason to suppose that claims like "I am a brain in a vat" could not turn out to be true. (shrink)

Note first that knowledge of one's own thought-contents would not count as a priori according to the usual criteria for knowledge of this kind. Surely, then, incompatibilists are using this term to refer to some other, stipulatively defined, epistemic property. But could this be, as suggested by McKinsey { 1 99 1: 9), the property of being knowable 'just by thinking' or 'from the armchair'? Certainly not if these were metaphors for knowledge attainable on the basis of reason alone, (...) since self-knowledge would fail to come out a priori in this sense. And exactly the same would happen if the property were that of being knowable by inference, since, according to a common intuition, self-knowledge is noninferential. (shrink)

The primary aim of this chapter is to evaluate whether considerations about a priori domains and abstract objects favor atheism over theism.

O objectivo deste artigo consiste em introduzir a noção de conhecimento a priori e os problemas que a envolvem. Começa-se por caracterizar o conhecimento a priori e aquilo que o distingue do conhecimento a posteriori para de seguida avaliar-se as dificuldades que uma compreensão adequada da noção de independência da experiência enfrenta. A noção de a priori é distinguida da de necessidade, à qual, tradicionalmente, tem sido associada. Por fim, o problema do a priori é formulado (...) e as principais teorias que a ele respondem brevemente discutidas. (shrink)

Based on the dispute between Protagoras and Socrates on the origin of ethics, one can ask the question of whether the principle of ethics is reason orfeeling/emotion, or whether ethics is grounded on reason or feeling/emotion. The development of Kant’s thoughts on ethics shows the tension between reason and feeling/emotion. In Kant’s final critical ethics, he held to a principle of “rational a priori.” On the one hand, this is presented as the rational a priori principle being the (...) binding principle of judgment. On the other hand, it is presented as the doctrine of “rational fact” as the ultimate argument of his ethics. Husserl believed that Kant’s doctrine of a rational a priori totally disregarded the a priori essential laws of feeling. Like Husserl, Scheler criticized Kant’s doctrine of a rational a priori, and therefore developed his own theory of an “emotional a priori”. Both of them focused their critiques on the grounding level of ethics. Scheler, however, did not follow Husserl all the way, but criticized him and reflected on his thoughts. At last, he revealed the primary status of a phenomenological material ethics of value. (shrink)

I look at incompatibilist arguments aimed at showing that the conjunction of the thesis that a subject has privileged, a priori access to the contents of her own thoughts, on the one hand, and of semantic externalism, on the other, lead to a putatively absurd conclusion, namely, a priori knowledge of the external world. I focus on arguments involving a variety of externalism resulting from the singularity or object‐dependence of certain terms such as the demonstrative ‘that’. McKinsey argues (...) that incompatibilist arguments employing such externalist theses are at their strongest, and conclusively show that privileged access must be rejected. While I agree on the truth of the relevant externalist theses, I show that all plausible versions of the incompatibilist reductio argument as applied to such theses are fundamentally flawed, for these versions of the argument must make assumptions that lead to putatively absurd knowledge of the external world independently of the thesis of privileged access. (shrink)

Carrie Jenkins (2005, 2008) has developed a theory of the a priori that she claims solves the problem of how justification regarding our concepts can give us justification regarding the world. She claims that concepts themselves can be justified, and that beliefs formed by examining such concepts can be justified a priori. I object that we can have a priori justified beliefs with unjustified concepts if those beliefs have no existential import. I then argue that only beliefs (...) without existential import can be justified a priori on the widely held conceptual approach. This limits the scope of the a priori and undermines arguments for essentialism. (shrink)

Sober and Elgin defend the claim that there are a priori causal laws in biology. Lange and Rosenberg take issue with this on Humean grounds, among others. I will argue that Sober and Elgin don’t go far enough – there are a priori causal laws in many sciences. Furthermore, I will argue that this thesis is compatible with a Humean metaphysics and an empiricist epistemology.

On rationalist infallibilism, a wide range of both (i) analytic and (ii) synthetic a priori propositions can be infallibly justified, i.e., justified in a way that is truth-entailing. In this paper, I examine the second thesis of rationalist infallibilism, what might be called ‘synthetic a priori infallibilism’. Exploring the seemingly only potentially plausible species of synthetic a priori infallibility, I reject the infallible justification of so-called self-justifying propositions.

In this article, I review textual evidence demonstrating that James and Dewey incorporated Kant’s ideas, even while criticizing him. I specifically argue that the pragmatic evolution of the Kantian a priori carried out by James and Dewey is a transition from the mental to the bodily. I further argue that the parallels between pragmatists and Kant, along with the transition from the mental to bodily, relate to scientific contexts in which all developed their outlooks. Though historically grounded, my ultimate (...) goal is to show that pragmatism and by extension Kantianism mesh with and indeed contribute to cutting edge ideas in fields ranging from neuropathology to robotics and AI to cognitive science, whether in the form of Gibsonian theory or enactivism. (shrink)

The aim of the present work is to demonstrate that physicalism and a priori knowledge are epistemologically incompatible. The possibility of a priori knowledge on physicalism will be considered in the light of Edmund Gettier’s insight regarding knowledge. In the end, it becomes apparent that physicalism entails an unavoidable disconnect between a priori beliefs and their justificatory grounds; thus precluding the possibility of a priori knowledge. Consequently, a priori knowledge and physicalism are epistemologically incompatible.