Two natural ideas we have about justification are that we are justified by basing our beliefs on good reasons, rather than wishful thinking or blind prejudice, and that justification makes our beliefs objectively likely to be true. Despite their appeal, respecting both of these ideas is impossible if we think that one's reasons for belief are determined entirely by one's psychological states, such as one's beliefs and experiences, and not by how the world is around one. If one's reasons are isolated from the world, it seems that they could not make our beliefs likely to be true.

This is why the debate between epistemic internalists, who think that justification is determined just by states of the believer, and externalists, who deny this, seems so intractable. Internalists are motivated by the intuition that justification is determined by the subject's reasons for belief, whereas externalists are motivated by the intuition that justification makes our beliefs objectively likely to be true.

I argue that the key to resolving this dispute is to reject the view that one's reasons are determined entirely by one's psychological states in favor of the view that one's reasons are facts - including facts of the world around one. We can then accept both the idea that justification is a matter of the subject's reasons for belief and the idea that justification makes one's beliefs objectively likely to be true. On this view one's reasons (the facts of the world around us) can make one's beliefs likely to be true. The result is a theory of justification that captures the motivations both of traditional forms of internalism and traditional forms of externalism, while avoiding the characteristic problems those views face.

Ordinarily when someone tells us about her psychological states, we presume that she is right. By deferring to her in this way, we treat her as a kind of authority on her own psychological life. Although a person usually has this authority, she lacks it whenever she takes a more detached, indirect, or third-personal point of view toward her psychological states. We see this, for example, when she learns about a belief or desire from a friend or therapist. For this reason an adequate account of the phenomenon of "first-person authority" must explain why we have it only for some but not all of our psychological states. Most philosophers believe first-person authority is an epistemic phenomenon, consisting in each of us being better situated to know about our own psychological states than anyone else. Against all such epistemic views, I argue that, because they base their accounts on epistemic privileges that are in principle available to anyone, they cannot capture the exclusively first-personal character of our authority.

As an alternative to the traditional approach, I argue that first-person authority is derived from a person's agency with respect to her own psychological states. By relating to her psychological states in a first-personal way, a person is able to change or maintain them directly on the basis of what she takes to be good reasons for them. Since no other person can affect her psychological states in this way, her capacities as an agent guarantee her a unique kind of authority for them. A person ordinarily expresses this kind of agential authority over her psychological states in what she says about them. This is what justifies our deferring to her psychological self-ascriptions. On the view I develop in this dissertation, first-person authority is not primarily a matter of special epistemic access to psychological facts and deference is not a response to the epistemic status of what someone says. It is an acknowledgment of the special role that a person's agency plays in determining her psychological life.

Deflationists have been hard at work convincing us that the concept of truth is far less interesting, and therefore far less mysterious, than long-lasting debates as to its true nature have made it seem. By denying that there is a substantive notion of truth expressed by our uses of the word `true,' deflationism promises to dissolve a number of explanatory hurdles.

Donald Davidson rejected deflationism. He grew increasingly sceptical of attempts to assimilate our understanding of truth to any definition or schema, and came to see his own approach to meaning as crucially dependent on a substantive notion of truth.

Exactly how, and where, does Davidson's approach to meaning depend on the availability of a substantive notion of truth? One of my goals is to answer this question. Another is to explain why it has proved so hard to answer it. A third goal is to bring to light what it would really be like to be a deflationist--in particular, what linguistic competence would look like if we took deflationism seriously.

In Chapter 1, I clarify Davidson's proposal to use truth theories as meaning theories. I explain this proposal as rooted in a certain conception of a meaning theory as an account of a speaker's understanding of her own sentences, and of this understanding as at least partly consisting in the speaker's knowledge of the truth-conditions of her sentences. In Chapter 2, I argue that deflationism does not allow us to describe competent speakers as knowing the truth-conditions of their sentences. If this is right, deflationism is incompatible with Davidson's conception of truth theories as theories of linguistic competence, but not for the reason usually given. That is, it is not because deflationism explains knowledge of truth-conditions as a trivial by-product of linguistic competence rather than being constitutive of it, since deflationism does not even allow us to ascribe such knowledge to speakers.

In Chapter 3, I argue against the widespread assumption that Davidson's proposal concerning the form to be taken by a meaning theory is primarily an answer to the question: what knowledge would enable us to interpret any utterance in a given language? This assumption underlies recent attempts to exhibit Davidson's approach to meaning as hospitable to a deflationary account of truth. However, as I explain, it undermines the distinction Davidson insists on between meaning theories and translation manuals, and thus cannot be right. Chapter 4 further argues that the methodology of radical interpretation does not, by itself, explain the need for a substantive notion of truth, contrary to what some (including Davidson) have suggested. Finally, in Chapter 5, I highlight some consequences of these results for both our understanding of Davidson's philosophy of language, and our understanding of deflationism.

We acquire beliefs on the basis of what others tell us all the time. If you tell me that your house is painted red, chances are that I will simply believe you without question; and if someone asks me what color your house is, I will simply tell her that it is red. Yet we do not seem to accept others’ testimony about beauty and art in the same way. If you tell me that the Taj Mahal is beautiful, or that Middlemarch is a great novel, it would be strange for me simply to adopt your view, even if I have a lot of confidence in your judgment. In order for me to be in a position to believe or to claim that the Taj Mahal is beautiful, or that Middlemarch is a great novel, I must experience these things myself—by going to Agra, or by reading the book.

My dissertation explains this apparent resistance to aesthetic testimony. I argue that aesthetic claims carry what is known in linguistics as ‘evidential’ information, to the effect that they are made on the basis of the subject’s firsthand experience. I locate aesthetic claims amongst a slew of other kinds of claims—including personal taste claims, perceptual appearance claims and moral claims—that all carry evidential information of this kind. These claims are loosely connected by having content that is essentially subjective or perspectival in some way, even when, as in the aesthetic and moral cases, there is also some claim to objectivity in play. I offer a detailed explanation in the aesthetic case—specifically for claims about beauty—of how their content comprises both subjective and objective elements. I argue that the evidential information carried by aesthetic claims and the other ‘perspectival’ claims I mention is communicated as conversational implicature, in spite of initial appearances to the contrary. Our apparent resistance to aesthetic testimony thus turns out to be an artifact of the evidential implications of aesthetic language: we often do accept aesthetic testimony, but we must describe our beliefs in a way that does not convey misleading evidential information.

I contend that Descartes's infamous commitment to God's free creation of the eternal truths plays an integral role in Descartes's philosophical program. Descartes's primary philosophical goal is to establish a method capable of yielding firm and lasting scientific knowledge. It isn't widely agreed that Descartes has been successful: first, his response to the threat of skepticism appears circular; and second, his account of God's free creation of eternal truths (e.g., mathematical and logical truths) seems to lead to paradox. I argue that neither criticism of Descartes is insuperable. In so arguing, I offer a novel interpretation of Descartes's project that rejects two common refrains of Cartesian scholarship. First, I deny that Descartes is an out-and-out internalist about knowledge and, in so doing, demonstrate that Descartes's epistemic program is not guilty of circularity. Second, I contend that Descartes's commitment to God's creation of the eternal truths is neither an embarrassment for Descartes nor a stand-alone curiosity, but is central to Descartes's epistemic program, modal theory, and scientific method.

In the Meditations, Descartes uses a method of doubt to reveal unshakable foundations upon which one can build scientific knowledge. Descartes's anti-skeptical procedure is commonly thought to be vulnerable to the charge that it is viciously circular. Descartes is accused of relying on a general epistemic principle (viz., the "truth rule": whatever I clearly and distinctly perceive is true) in his argument for the existence of a non-deceptive God, who in turn secures this very principle. In the first section of my dissertation, I explain that Descartes avoids circularity since he is able to achieve certainty and knowledge (cognitio) even before he becomes aware of the foundations of this knowledge. By attaining cognitio of God's existence and non-deceptive nature, Descartes can then make use of the "truth rule" and thereby ascend to perfect certainty and scientific understanding (scientia). In this way, Descartes can be seen to be an epistemic externalist. While Descartes's account thereby avoids circularity, it makes the epistemic advantage of the Cartesian scientist over the "atheist geometer" (an expert who does not believe in God but nonetheless achieves cognitio by using God-guaranteed clear and distinct perception) look quite thin. To fully appreciate the epistemic advantage of the Cartesian scientist - and thus the value of Descartes's epistemic program - one must recognize that God is not only the guarantor of one's cognitive faculties, but also the metaphysical foundation of scientific truths.

A second major objection to Descartes's anti-skeptical and scientific programs focuses on his infamous Creation Doctrine: the doctrine that God freely wills and creates the eternal truths. The Creation Doctrine seems to lead to a paradox: Descartes's claim that God freely wills necessary truths seems to entail that these truths are both necessary (since God willed them to be necessary) and non-necessary (since God could have refrained from willing them). I argue that the sense in which the eternal truths could have been otherwise in no way threatens our certainty and knowledge of that which we clearly and distinctly perceive to be necessarily true.

In the final section of the dissertation, I further examine Descartes's Creation Doctrine. Descartes's goal of scientia involves not merely recognizing what is true, which is sufficient for cognitio, but also having full understanding of the foundations of knowledge and the relationships between truths. Descartes's scientific method thus requires intuitive foundations from which we can deductively arrive at further knowledge. According to this method, by understanding the way in which eternal truths have their origin in God's will and creation, we gain an appreciation of the connections between various truths and arrive at a systematic understanding of the world. Descartes denies that truths in various domains can be fully understood independent of a background of knowledge of simple and evident natures. He hopes to attain a "universal wisdom" and be able to deduce effects from their causes. I provide a demonstration of this method by considering Descartes's deduction of the laws of nature (inertia, collision, and rectilinear motion) from our knowledge of God's nature as immutable, the nature of matter as extension, and the fact that God has created a physical world with variation in its parts.

It is common to accept subjectivism about matters of gustatory taste, the view that gustatory reasons and the truth of gustatory judgments are essentially dependent on our tastes or interests. In this dissertation, I argue against this commonplace by suggesting that examination of our gustatory practices does not drive us to gustatory subjectivism. I take up four aspects of our practices.

First, we acquire new tastes. The acquisition of taste is, I suggest, done on the basis of gustatory reasons that are not essentially sourced in our tastes or interests. Subjectivism cannot allow such reasons, and understanding taste acquisitions in this manner allows us to make sense of certain "second-order" evaluative attitudes we take towards those acquisitions.

Second, we resist accepting gustatory testimony, which may suggest that gustatory reasons are dependent on one's tastes. I argue against this suggestion by appealing to a gustatory value: that of abiding by one's own tastes. This gustatory value comes into conflict with epistemic values that demand that we believe reliable testimony, and this conflict makes sense of our resistance without presupposing subjectivism.

Third, we nonchalantly engage in intractable taste disputes, which may again suggest that gustatory reasons are dependent on one's tastes. However, without presupposing subjectivism, we can make sense of our nonchalance in terms of the dialectical nonchalance we feel when we are faced with disagreements that inevitably violate their constitutive goal: that of resolution via non-question-begging arguments.

Fourth, we compare and adjudicate between very different gustatory values. If those values are not measurable on a single scale, such "superhard" comparisons may motivate a subjectivist understanding of gustatory reasons. Here I suggest that the sense that such comparisons might motivate subjectivism derives from the inaccurate assumption that rational comparisons must be made on the basis of an independent guide. Giving up the assumption, we can construe such comparisons case-by-case as ones in which either one side trumps the other overall, or reason is simply indifferent between them.

Why do your self-attributions of beliefs and intentions ordinarily constitute authoritative self-knowledge? You can self-attribute a belief or an intention transparently. For instance, you can transparently self-attribute a belief that p by judging that p. You can transparently self-attribute an intention to Φ by deciding to Φ. However, recognizing just this much does not completely explain the epistemology of transparent self-attributions.

Self-attributions of this kind count as authoritative knowledge because they involve a form of practical knowledge. You can intentionally control the kind of attitude you take up in conscious thought, and when you do that, you know what kind of attitude you are taking up in conscious thought. Then, in the context of transparent self-attribution of belief or intention, a judgment that p or a decision to Φ can have a complex identity. A judgment that p can also be a self-attribution of a belief that p, and a decision to Φ can also be a self-attribution of an intention to Φ. To explain how this can be the case I introduce the linked notions of embedded mental action and content plurality.

The view of self-knowledge that emerges also explains why there are contents involving belief attributions that are absurd to assert or to judge even though they can be true. These contents are Moorean absurdities for belief. I argue that there are no corresponding Moorean absurdities for intention, even though you also have transparent self-knowledge of what you intend to do. This points to an important attitudinal distinction between belief and intention: intentions are not beliefs.

The difference between first-personal and third-personal methods of attributing attitudes is subtle. The specialness of the first-personal perspective cannot be explained in terms of epistemic groundlessness, as many have tried to do. You must also make third- personal groundless attributions of belief to understand others’ intentional behavior.

Despite philosophical skepticism on this point, transparent self-knowledge really is valuable, in a special sense. Having complete diachronic transparent self-knowledge involves having no hidden attitudes and having a diachronically unified self of the kind that is required for evaluation in terms of authenticity.

The epistemology of self-knowledge relies crucially on the fact that you can do things in thought. Knowing yourself is something you do because intentional action is indispensable to authoritative, knowledgeable self-attribution of beliefs and intentions.

In this dissertation, I develop a novel account of spatial experience that—unlike most contemporary theories of perception—situates our experience of space within a broader context of non-sensory cognitive activities. On my account, to perceive an object as square is, in part, to deploy an a priori Euclidean concept of squareness – a concept that features in, but is not derived from, experience. I use this rationalist analysis of spatial experience to shed light on three issues: the connection between Euclidean proof and our perception of physical objects; the distinction between primary and secondary qualities; and the challenge posed to the veridicality of our spatial experience by the findings of relativistic physics.

In light of the discovery of consistent non-Euclidean geometries and the empirical evidence that our own universe is not perfectly Euclidean, many have rejected the Kantian idea that Euclidean proof gives us a priori knowledge of physical space. But there does seem to be a cognitive connection between the theorems we prove in Euclidean geometry and the spatial features we perceive physical objects to have: having proven the Pythagorean theorem, a carpenter will expect a particular relation to hold among the lengths of the sides of a right triangle she is constructing from wooden beams. This suggests that we represent the empirical objects we perceive as subject to the results we obtain in the domain of Euclidean geometry, even if we no longer think that such representations are guaranteed to be correct.

In order to account for this phenomenon, I develop a view on which the concepts we employ in Euclidean proof are a priori, but also feature in perception. After setting out the motivations for this view and offering a brief sketch of its contours, in Chapter 1, I go on to defend its central claims in Chapters 2 and 3. I argue that our use of spatial concepts in Euclidean geometry shows that they cannot be derived from experience: certain aspects of these concepts, such as the idea of continuity built into our concept of a circle, outstrip anything we can glean from our sensory cognition. At the same time, I suggest, an experience of an object as square is one that deploys our a priori concept of squareness, and does so simply in virtue of its phenomenal character. That is, such an experience, independent of any causal relations it might bear to objects in the external world, represents its object as instantiating the very geometrical property about which we reason in Euclidean proof. It is this fact that explains why the carpenter takes the results of her a priori reasoning to apply to the empirical objects she perceives – her experience of shape has specific geometrical content built into it, in virtue of the a priori Euclidean concepts that feature in its content.

This account of spatial experience helps shed light on a topic with a long philosophical history: the distinction between primary and secondary qualities. In Chapter 4, I argue that, lacking any a priori grasp of a secondary quality like redness, we can represent that property only by way of its role in experience – as whatever property plays the relevant role in generating experiences of red. Since perception does not inform us which specific property is playing that role, we are left in the dark about the nature of the secondary qualities. By contrast, in the case of a primary quality like squareness, we are not constrained to represent the property by way of its role in experience. When we experience an object as square, we grasp the nature of the property represented, in virtue of our a priori concept of squareness – the property of having four equal sides joined at four right angles. Color and shape, then, feature in our cognitive lives in very different ways; these conceptual and experiential differences are, I contend, the real basis of the distinction between primary and secondary qualities.

In the final chapter of the dissertation, I consider how, on my account, we should evaluate the veridicality of our experience of shape in light of Einstein’s special theory of relativity (STR). According to the standard interpretation, STR reveals that no purely spatial properties are instantiated in our universe; instead, all that objectively exists is a four-dimensional spatiotemporal manifold. Since, on my account of spatial perception, our experience represents the presence of purely spatial properties—the Euclidean properties about which we reason in performing abstract proof—STR might seem to imply that our spatial experience is never veridical. Against this, I argue that STR gives us no reason to abandon the idea that the Euclidean spatial properties represented in our experience are in fact physically instantiated. Instead, what Einstein’s discoveries show is that those properties are instantiated in a particular manner: namely, relative to various inertial frames of reference. This analysis allows us to hold onto the intuitive idea that there is a tight connection between our a priori geometrical reasoning and our experience of space, without being forced to accept that our spatial experience is universally illusory.