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^I.19 We begin the book by discussing an ancient puzzle: the Regress Problem. The Regress Problem has to do in the main with the justification of belief. Recall from our discussion in Section I.1 of the nature of knowledge that most epistemologists think that knowing a proposition has to involve something in addition to simply believing a proposition that turns out to be true. (If knowledge didn't require this, there'd be no clear difference between knowledge and lucky guesses.) The idea we noted in passing is that knowing a proposition requires (at least) possessing a justified true belief where justification (of the sort relevant to knowledge, as opposed to, say, moral goodness) means something like being “backed by good reasons.” The Regress Problem takes this idea as a starting point and then shows how things can get very awkward very quickly. Just suppose, for example, that a given belief is justified only if it is supported by further beliefs. Now here's a question: must these further beliefs themselves be justified? If not, it's hard to see how the original belief would be justified. But if so, then they too must be backed by good reasons. Taking this idea to its logical conclusion indicates (bizarrely) that a belief is justified only if it's backed by an infinite number of good reasons – something it's not obvious that we actually have. Once this puzzle is set out, various solutions to it are canvassed: coherentism, infinitism, and foundationalism. As we'll see, foundationalism is shown to have certain advantages over the other two options.

^I.20 On the foundationalist view, some justified beliefs are justified without requiring support from further beliefs. In some cases, as the foundationalist has it, perceptual experiences (e.g. your seeing a table in front of you) suffice to play the justification‐conferring role for some non‐inferential justified beliefs (i.e. beliefs that are both justified but not based on other justified beliefs). But does perceptual experience really have what it takes to stop the regress of justification? If so, how, exactly, does that work? Chapter 2 tries to get a grip on these issues. In the course of doing so, we delve into the matter of what kind of a thing perceptual experience is, and how the nature of perceptual experience connects to the matter of whether and how it can provide us with reasons for believing things.

^I.21 Even if it turns out that perceptual experiences really are good enough to stop the regress and thus to justify beliefs non‐inferentially, it is worth asking whether that anything that justifies a justified belief must derive in some way from experience – for example, perceptual, introspective, or otherwise. The matter of whether (and if so, why; if not, why not) the answer is “yes” or “no” will be the guiding topic explored in Chapter 3, and it's one that has been divisive in epistemology from the early‐modern period onward. Proponents of a priori justification allow that at least some beliefs may be non‐experientially justified – that is, that they are such that the source of their justification is, in some relevant way, independent of experience. Beliefs whose justification (non‐trivially) derives from experience are justified a posteriori. The question of whether all justified beliefs are justified a posteriori (and whether some might be justified a priori) has marked a long‐standing distinction in philosophy between two epistemological traditions: rationalism and empiricism. Chapter 3 aims at giving readers a grounding in this.

^I.22 In Chapter 4, we explore ways of using reasoning to gaining new justified beliefs and knowledge from the ones we have. It should be unsurprising that we can't gain new justified beliefs through bad reasoning (even if the beliefs bad reasoning generates happen sometimes to be true). But just how good does the reasoning have to be, exactly? At one end of the spectrum, we might think that the kind of reasoning that's needed to get us from one justified belief to another must be conditionally infallible; a given inference rule is conditionally infallible if it's impossible to reason in accordance with the rule to a mistaken belief if all of the beliefs you reason from are correct. We canvass some worries for both the necessity and sufficiency of conditionally infallible rules for extending our justification and knowledge; in the course of doing so, we engage with (among other things) deductive and inductive reasoning, Hume's problem of induction, and closure principles.

^I.23 As we noted in Section I.1, epistemologists are interested in knowledge, and not merely in justification. While Chapters 1–4 concern mostly issues to do with epistemic justification (with some cursory discussions of propositional knowledge), Chapter 5 looks knowledge square in the face. In particular, Chapter 5 concerns the nature of knowledge. Recall from Section I.1 the view that knowledge = justified, true belief:

K=JTB: you know that p iff (i) p is true, (ii) you believe p, and (iii) you are justified in so believing.

As we noted, the JTB view of knowledge is no good because knowledge requires something in addition to JTB. Chapter 5 explains why this is, and introduces what are called “Gettier cases” – cases that show, pretty darn convincingly, that a person could have a justified true belief that p but still fail to know that p. What these Gettier cases suggest is that we need to figure out what else knowledge requires. Three conditions that have been proposed for dealing with Gettier cases are a causal condition, a modal condition, and an ability or virtue condition. We discuss the prospects of all three; in light of some of the problems with each, we also outline a less optimistic idea: that perhaps it was a mistake to initially attempt to provide a non‐circular informative analysis of knowledge in terms of its constituent parts.

^I.24 Chapters 6 and 7 concern two sources of knowledge beyond perception: memory and testimony. These are both very important. Much of what we believe is on the basis of what others (friends, teachers, experts, etc.) tell us; and without memory we wouldn't believe or know anything we do (perceptual, testimonial, or otherwise) for long enough to act on it successfully. In Chapter 6, which concerns memory, we explore in some detail the connection between two kinds of memory, episodic and factual, and their roles in the justification of belief and retention of knowledge. In the course of doing so, we consider a number of competing views concerning the role that apparent memories play in the justification of belief. These debates interact with issues that matter for the proper formulation of foundationalism and to the internalism–externalism debate, to which we'll return in Chapter 9. One important issue that arises in connection to discussions of all potential sources of knowledge and of justification has to do with the possibility of justifying our reliance on sources. The case of memory shows in a particularly clear way the difficulty of justifying our reliance on a source, and this matters to skeptical challenges to our reliance on other sources, such as testimony, the a priori, and various forms of inference.

^I.25 In Chapter 7, our focus is beliefs formed via the testimony of others. Take as a starting point that we all have relied extensively on testimony for most of our lives, and (relatedly), by relying on testimony, we have acquired an impressive body of knowledge that we surely could not have acquired without relying on testimony. This all seems right. But it also seems right that it is inappropriate to trust others when we do not have independent positive reasons to think that the testimony we rely on is reliable. But – as we explain – when you put all these ideas together, you get a puzzle. It's a puzzle that has perplexed thinkers from Thomas Reid and David Hume to the present day. One thing is for sure: satisfactorily escaping this puzzle requires taking some sort of “stand,” and contemporary social epistemologists often distinguish themselves as reductionists and non‐reductionists in light of which stand they take. The debate between reductionists and non‐reductionists overlaps imperfectly with debates about what are called epistemic transmission principles. Chapter 7 digs in to the details of these debates and concludes with a brief overview of some additional testimony‐related themes in contemporary social epistemology concerning (i) peer disagreement, (ii) epistemic norms governing assertion, and (iii) testimonial injustice.

^I.26 In Chapter 8, we return to knowledge, albeit not in a standard way. Up to Chapter 8, when we discuss knowledge, we discuss specifically propositional knowledge. But there are (at least) three very different and interesting ways in which contemporary epistemology has investigated kinds of knowledge beyond standard propositional knowledge. These concern the relationships between (i) knowing how and knowing that, (ii) knowledge and understanding, and (iii) what Ernest Sosa calls animal knowledge and reflective knowledge. The principal aim of this chapter, entitled “Kinds of Knowledge,” is to discuss and critically evaluate some of the motivations for, and criticisms of, each of these distinctions.

^I.27 The focus of Chapter 9 is a long‐standing and deeply entrenched debate that concerns, in the main, epistemic justification, but also knowledge by extension (in so far as knowledge requires justification). The key divide Chapter 9 explores is between what are called epistemic internalists and epistemic externalists. To be an internalist about justification is to believe either (i) that a thinker's mental states wholly determine whether what the thinker has justification to believe (mentalism) or (ii) that that which is accessible by reflection to the thinker wholly determines what she has justification to believe (accessibilism). Externalists, by contrast, simply deny internalism under one (or both) of these descriptions. For example, according to one prominent version of epistemic externalism, what determines whether a belief is justified or not is whether the process that produced the belief was a reliable one. As we'll see in this chapter, many of the key themes that divide internalists and externalists about epistemic justification mirror themes that feature analogously in discussions about moral luck and responsibility.

^I.28 In Chapter 10, we turn our focus to some puzzles that arise at the intersection of the epistemology and ethics of belief. We take, as a starting point for discussion, W.K. Clifford's famous dictum that “It is wrong always, everywhere, and for anyone to believe anything upon insufficient evidence” (1877, p. 295). Is what Clifford says true? What kinds of considerations are relevant to determining this? As we'll see, if Clifford's principle is understood as a kind of moral principle, one that tells us that there's always a decisive moral reason to believe only what you have sufficient evidence to believe, it looks like Clifford's principle faces some serious problems. If, however, the evidentialist principle is understood as a kind of purely epistemic principle, one that says that there is something epistemically defective about believing something without sufficient evidence, the principle has more plausibility. This chapter navigates a range of terrain surrounding these issues, and, more generally, delves in questions about how “ought” and “should” apply to beliefs in light of the fact that what we believe is (to some extent) outside of our direct control.

^I.29 By this point in the book, the reader should have a pretty good sense of what epistemology is all about. It would be convenient to end here. But doing so would be cheating. Remember the skeptic we described in Section I.1? We simply registered that the skeptic has some pretty powerful arguments, even if the skeptical conclusion these arguments lead to seems disastrous. The time has finally come – we can put it off no longer – to lock eyes with the skeptic and see whether we can make it out with any of our knowledge intact.

^I.30 There are various kinds of skeptical arguments. But one strand is the most powerful of them all: radical skeptical arguments. In Chapter 11, we – taking Descartes' engagement with radical skepticism as a starting point – sharpen the challenge and show how this closure principle (which we'll have seen crop up at various places in the book) features in the argument. We then consider three overriding anti‐skeptical strategies: (i) the Moorean strategy, (ii) the anti‐closure (sensitivity) strategy, and (iii) the explanationist strategy. These strategies are “overriding” anti‐skeptical strategies in the sense that they simply take radical skepticism’s argument at face value then attempt to meet it head‐on. Along with these overriding strategies, we also engage with what is probably the most well‐known undercutting anti‐skeptical strategy: attributor contextualism. The contextualist's line against the skeptic is a kind of “undercutting” anti‐skeptical strategy in the sense that it involves (through some creative linguistic moves) maintaining that what looked initially like a kind of paradox is in fact not a paradox at all. We conclude by investigating some less orthodox skeptical strategies: one from Jonathan Schaffer which appeals to what he calls the “debasing demon,” and one which appeals not to hypothetical or far‐off examples but, rather, to the various kinds of cognitive biases that recent empirical psychology tells us are pervasive in our thinking.

^I.31 Taken together, the chapters cover a lot of ground. But let us not get ahead of ourselves. The “is” in This Is Epistemology should not be read as the “is” of identity (a reading that would mean, rather arrogantly, that epistemology is all and only what we've told you about), but as the “is” of predication (which just means, much more modestly, that all of these things are examples of epistemology). To be sure, there are a lot of topics that count as serious epistemology and which we simply haven't managed to cover here in sufficient detail or at all. Accordingly, we encourage the interested reader to explore both more broadly and more deeply, and we hope that the present text offers a suitable background and guidance for doing so well.