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A Guide

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A Guide

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"This is a superb companion to Epistemology: An Anthology. It consists of sixty commentaries, one for each of the sixty entries in that anthology. Turri is an extremely lucid writer, with a wonderful knack for finding and laying out argumentative structure, and for explaining crucial concepts. His commentary will greatly aid student comprehension and enhance class discussion."
Ernest Sosa, Rutgers University

"Turri's discussions are engaging and lucid. They are written for beginning students and will serve that purpose beautifully, but they are so well done that even veteran epistemologists will find them helpful."
John Greco, Saint Louis University

Epistemology: A Guide is a straightforward and accessible introduction to contemporary epistemology for those studying the topic for the first time. It introduces and explains the main arguments of the most influential publications in the field from the last 50 years.

Balancing simplicity of argument with accuracy and detail, this guide covers the central topics of theory of knowledge, including skepticism, epistemic justification, epistemic closure, virtue epistemology, and naturalized epistemology. Instead of artificially treating themes in isolation, it provides a clear context for key topics and concepts. Designed to stand alone or to accompany the second edition of Epistemology: An Anthology (Wiley Blackwell, 2008), this is a deft and concise introduction to a foundational topic in philosophy.

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§ 1

The best case for skepticism about the external world? (Stroud, “The Problem of the External World”)

We’re all intimately familiar with what goes on in our own minds. We make plans, form opinions, experience pleasure and pain, and so on. It’s also natural to suppose that we know a lot about what goes on outside our own minds too, about the world around us, based on the information we get through our senses of sight, hearing, smell, taste, and touch. Natural as that idea may be, it’s surprisingly easy to get yourself into a skeptical frame of mind about the possibility of such knowledge. Can we really know anything about the world outside our own minds?
Barry Stroud aims to understand the attraction of skepticism about the external world, why knowledge of the external world based on sense experience poses a philosophical problem. To accomplish this, he focuses intensely on the argument presented at the beginning of Rene Descartes’s Meditations on First Philosophy (published originally in 1641), the most influential work of one of the most influential philosophers of all time.
Let’s note a couple important points before we proceed. First, people who reflect on knowledge nearly unanimously agree that knowledge requires truth, or as it’s sometimes put, that knowledge is factive.1 This means that we can know something only if it is true or a fact. We cannot know a falsehood. (We can of course believe a falsehood, but that’s a different matter.) Now if you think that knowledge is not factive, I recommend a simple solution: everywhere we here speak of “knowledge,” understand it to mean “knowledge of the truth,” and every time we claim or ask whether someone “knows that so-and-so,” understand it to mean “knows it’s true that such-and-such.” Second, something can be possible without being real or actual. Indeed lots of things are possible that aren’t actual. For instance, it’s possible for winged horses to exist, even though none actually do. Likewise for wizards, dragons, phlogiston, the luminiferous ether, etc. With those points in mind, let’s proceed.
Imagine Descartes at work in his study on a cold night, sitting a few feet from a comforting fire. Unsure for the moment how his narrative should best proceed, he takes a break and turns his attention to the fire. He sees its colorful flames flitting and flickering; he hears it crackling and popping; he feels its heat emanating; he smells the fragrant wood burning. In light of all this, Descartes of course believes he’s near a fire. But do these sense experiences enable him to know he’s near a fire?
It’s hard to imagine Descartes’s senses putting him in a better position to gain knowledge of the external world. He is as well-positioned as any of us could ever hope to be. So if the answer to our question at the end of the previous paragraph is “No,” then it seems very likely that we never know anything about the external world, at least by way of our senses.
The way things look, sound, smell, and feel make it appear to Descartes as though he’s near a fire, and it’s this appearance that he trusts when judging that he’s near a fire. But of course things might appear exactly the same in a perfectly realistic dream. And a perfectly realistic dream is a genuine possibility. It’s certainly possible for him to have all those sensations despite merely dreaming that he’s near a fire. Indeed, any sensory experience might be a mere component of a perfectly realistic dream. Thus sense experience, being equally compatible with dreaming or waking, could never enable him to know that he is awake rather than merely dreaming.
As Descartes recognizes, if he’s merely dreaming that he’s near a fire, then he certainly doesn’t know that he’s near a fire. And he also recognizes it is at least possible that he’s merely dreaming. So he knows that a certain genuine possibility, the dream-possibility (as Stroud calls it), is incompatible with his knowing that he’s near a fire. So in order to know that he’s near a fire, he must know that the dream-possibility is false.
Notice that, on this way of thinking, in order for the dream-possibility to potentially threaten Descartes’s knowledge of the fire, he doesn’t need to know, or even so much as believe, that it is actually true. No, the dream-possibility threatens simply because Descartes recognizes that it is possibly true, and that if it were actually true, he wouldn’t know that he’s near a fire.
Could Descartes ever come to know that the dream-possibility is false? Sense experience itself won’t enable such knowledge because, as we’ve already said, any sense experience is perfectly compatible with the dream-possibility. But isn’t there some test he could perform to determine whether he is merely dreaming? Unfortunately not, because in order for him to learn from the test, he’d need to know that he wasn’t merely dreaming that he was performing the test!
If you’re wondering why he couldn’t then just perform a second test to determine whether he’s merely dreaming that he performed the first test, consider: he could equally well be dreaming that he’s performing the second test. The same is true for a third test he might perform to determine whether he’s merely dreaming that he performed the second test. And so on. No matter how many tests he performs, the same problem recurs. And since it’s not possible to perform an infinite series of tests, we find no relief in this direction.
Let’s encapsulate the preceding line of thought in the following argument, broken up into two parts to enhance clarity. The main argument goes like this:
1. If Descartes doesn’t know that he’s near a fire, then we never know anything about the external world. (Premise)
2. Descartes doesn’t know that he’s near a fire. (Premise)
3. So we never know anything about the external world. (From 1 and 2)
The argument is logically valid: if its premises are true, then its conclusion must be true too. That leaves us to ask whether its premises are true. 1 is at least very plausible, and Stroud is willing to grant it. That leaves only 2 to seriously question. The following supplementary argument supports 2:
a. Descartes knows that the dream-possibility is incompatible with his knowing that he’s near a fire. (Premise)
b. If Descartes knows that a possibility is incompatible with his knowing some specific claim, then in order for him to know the specific claim, he must know that the possibility in question is false. (Premise)
c. So in order for Descartes to know that he’s near a fire, he must know that the dream-possibility is false. (From a and b)
d. But Descartes couldn’t know that the dream-possibility is false. (Premise)
e. So Descartes doesn’t know that he’s near a fire. (From c and d)
Notice that (e) is exactly the same as 2.
Should we accept this argument? Stroud wonders whether we can seriously entertain the skeptical conclusion expressed by 3, because it’s allegedly either absurd or even unintelligible. But merely rejecting it as absurd or unintelligible deprives us of the opportunity to learn something potentially important about knowledge (or at least about our concept of knowledge). Accordingly, he challenges those of us inclined to reject the conclusion to locate the argument’s flaw. Whatever it is, it isn’t obvious.
Stroud suggests that (c) is false. Yet (c) follows from (a) and (b), so rejecting (c) requires us to reject at least one of (a) and (b). (a) is obviously true, which leaves (b).
The problem is that (b) is arguably “embodied” in our ordinary procedures for “making and assessing knowledge-claims.” Consider for instance a bird watcher who judges a certain bird to be a goldfinch. We ask her why she thinks it’s a goldfinch. “Because it’s yellow,” she says. “But for all you’ve said,” we respond, “it’s possible that it’s a canary – canaries are yellow too.” We don’t think she knows it’s a goldfinch, because she knows very well that canaries aren’t goldfinches, and yet she doesn’t know it’s not a canary. She must rule out this relevant possibility, the canary-possibility, in order to know it’s a goldfinch.
The question then becomes whether the dream-possibility is in all relevant respects similar to the canary-possibility, so that when we insist that the bird watcher must rule out the canary-possibility, we thereby commit ourselves to insisting that Descartes must rule out the dream-possibility. Does Descartes have to rule out the dream-possibility in order to know there’s a fire nearby, as the bird watcher must rule out the canary-possibility in order to know that she’s looking at a goldfinch? If not, why not? Each subject knows the possibility in question is incompatible with his or her knowing the claim in question. So what could be the difference?
A plausible explanation of the difference, should there be any, would go a long way toward resolving “the problem of the external world.” Therein lies the challenge, and potential reward, of confronting philosophical skepticism.


Allan Hazlett, “Factive Presupposition and the Truth Condition on Knowledge,” Acta Analytica 27.4 (2012): 461–478.
John Turri, “Mythology of the Factive,” Logos & Episteme 2.1 (2011): 143–152.
Stroud, Barry, “The Problem of the External World,” Chapter 1 in The Significance of Philosophical Skepticism (Oxford: Clarendon Press, 1984). © 1984 by Barry Stroud.
1 For some recent controversy over the “truth requirement” on knowledge, see Allan Hazlett, “Factive Presupposition and the Truth Condition on Knowledge,” Acta Analytica 27.4 (2012): 461–478, and John Turri, “Mythology of the Factive,” Logos & Episteme 2.1 (2011): 143–152.

§ 2

Proving the external world exists (Or: Let’s all give Moore a hand!) (Moore, “Proof of an External World”)

Suppose we disagree about the number of books on the desk. You say there are at least two. I disagree. And it’s no mere verbal disagreement – we’re referring to the same desk, and mean the same thing by “book” and “at least two,” etc. How might you prove your point?
Here’s one way. You walk over, point to one book sitting on the desk, and then point to another, all while saying, “Here’s one book on the desk, and here’s another. So there are at least two books on the desk.” I couldn’t rightly criticize the proof. I’d have to concede the point. What else could I possibly be looking for in a proof? Your premises (“here’s one book the desk, and here’s another”) are different from your conclusion (“there are at least two books on the desk”), in which case you didn’t simply beg the question. Your conclusion follows straightforwardly from your premises, and you know that it does. And you obviously know the premises – after all, you aren’t blind, you’re looking right at the books, and you’ve correctly verbally identified them. Without question, your proof perfectly settles the matter in your favor.
Immanuel Kant, perhaps the most influential of all modern philosophers, once said it was “a scandal to philosophy” that the existence of real, mind-independent external objects “must be accepted merely on faith” rather than a “satisfactory proof.”1 Kant thought he had rescued philosophy from scandal by giving such a proof, indeed, the only possible such proof. Setting aside the merits of Kant’s own proof, G.E. Moore denied that Kant’s was the only possible such proof. A much simpler and fully convincing proof is readily available.
Moore offers his proof by saying, “Here’s one hand, and here’s another. So external objects exist,” as he gestures and holds his hands up before us. This proof, Moore says, is “perfectly rigorous.” It meets the three criteria we noted earlier when discussing your proof about the number of books on the desk. Its premises are different from its conclusion; its conclusion follows, as Moore knows, straightforwardly from its premises; and finally, Moore obviously knows the premises.
Might a satisfactory proof require more than meeting those three criteria? Not if our ordinary practice is any indication. As with your earlier proof about the books, we “constantly take proofs of this sort as absolutely conclusive.”
Note an interesting connection with Stroud’s discussion from §1. We wondered whether Descartes was right to claim that he must know the dream-possibility is false in order to know that he’s near a fire. And Stroud worried that Descartes was indeed right about that, because such a requirement might be “nothing more than an instance of a general procedure we recognize and insist on in making and assessing knowledge-claims in everyday” life, which procedure helps to define out concept of knowledge. Here Moore appeals to our everyday procedures for offering and evaluating proofs.
Moore anticipates that some will say his so-called proof fails. One type of critic insists that in order for Moore’s proof to really succeed, he must also prove his premises – prove that here is one hand and that here is another. If this critic is right, then the three criteria we earlier identified aren’t sufficient for a conclusive proof after all. At least sometimes, a conclusive proof requires more. Moore rejects this, and explicitly disavows any intention to prove his premises. He doubts it could be done, because proving them requires proving that he’s not merely dreaming that he has hands. And even though he has “conclusive reasons” (or “conclusive evidence”) that he’s not merely dreaming, he cannot articulate that evidence to us, which he of course must do in order to offer a proof.
One is reminded of a scene in Robert Louis Stevenson’s The Strange Case of Dr. Jekyll and Mr. Hyde. A shaken and ill Jekyll tells his friend Utterson that Mr. Hyde “will never more be heard of.” When Utterson suggests – rightly, it turns out, as the story subsequently unfolds – that Jekyll’s assertion might not be entirely warranted, Jekyll replies, “I have grounds for certainty that I cannot share with anyone.”2 What does Jekyll mean by “cannot” here? He might mean that he cannot prudently sh...

Table of contents

  1. Cover
  2. Title page
  3. Copyright page
  4. Dedication
  5. Preface
  6. Acknowledgments
  7. § 1 The best case for skepticism about the external world? (Stroud, “The Problem of the External World”)
  8. § 2 Proving the external world exists (Or: Let’s all give Moore a hand!) (Moore, “Proof of an External World”)
  9. § 3 Some ways of resisting skepticism (Moore, “Four Forms of Scepticism”)
  10. § 4 Plausibility and possibilities (Moore, “Certainty”)
  11. § 5 Skeptic on skeptic (Klein, “How a Pyrrhonian Skeptic Might Respond to Academic Skepticism”)
  12. § 6 Realism in epistemology (Williams, “Epistemological Realism”)
  13. § 7 Socratic questions and the foundation of empirical knowledge (Chisholm, “The Myth of the Given”)
  14. § § 8–9 The foundation of empirical knowledge? (Sellars, “Does Empirical Knowledge Have a Foundation?” and “Epistemic Principles”)
  15. § 10 It’s not a given that empirical knowledge has a foundation (BonJour, “Can Empirical Knowledge Have a Foundation?”)
  16. § 11 Interpretation, meaning and skepticism (Davidson, “A Coherence Theory of Truth and Knowledge”)
  17. § 12 Blending foundationalism and coherentism (Haack, “A Foundherentist Theory of Epistemic Justification”)
  18. § 13 Foundationalism, coherentism and supervenience (Sosa, “The Raft and the Pyramid”)
  19. § 14 Infinitism (Klein, “Human Knowledge and the Infinite Regress of Reasons”)
  20. § 15 The Gettier problem (Gettier, “Is Justified True Belief Knowledge?”)
  21. § 16 Some principles concerning knowledge and inference (Harman, Thought, Selections)
  22. § 17 The essence of the Gettier problem (Zagzebski, “The Inescapability of Gettier Problems”)
  23. § 18 Knowledge is an unanalyzable mental state (Williamson, “A State of Mind”)
  24. § 19 Closure, contrast and semi-skepticism (Dretske, “Epistemic Operators”)
  25. § 20 Closure, contrast and anti-skepticism (Stine, “Skepticism, Relevant Alternatives, and Deductive Closure”)
  26. § 21 Keeping close track of knowledge (Nozick, “Knowledge and Skepticism”)
  27. § 22 Moore wins (Sosa, “How to Defeat Opposition to Moore”)
  28. § 23 The closure principle: dangers and defense (Vogel, “Are There Counter examples to the Closure Principle?”)
  29. § 24 Evidentialist epistemology (Feldman and Conee, “Evidentialism”)
  30. § 25 Non-defensive epistemology (Foley, “Skepticism and Rationality”)
  31. § 26 Reliabilism about justification (Goldman, “What Is Justified Belief?”)
  32. § 27 Reliabilism: a level assessment (Vogel, “Reliabilism Leveled”)
  33. § 28 Against externalism (BonJour, “Externalist Theories of Empirical Knowledge”)
  34. § 29 Against internalism (Goldman, “Internalism Exposed”)
  35. § 30 A skeptical take on externalism (Fumerton, “Externalism and Skepticism”)
  36. § 31 A friendly take on internalism (Feldman and Conee, “Internalism Defended”)
  37. § 32 Warrant (Plantinga, “Warrant: A First Approximation”)
  38. § 33 Intellectual virtues (Zagzebski, Virtues of the Mind)
  39. § 34 Virtue epistemology (Greco, “Virtues and Vices of Virtue Epistemology”)
  40. § 35 Knowledge, luck and virtue (Pritchard, “Cognitive Responsibility and the Epistemic Virtues”)
  41. § 36 Epistemic value and cognitive achievement (Sosa, “The Place of Truth in Epistemology”)
  42. § 37 Giving up on knowledge (Kvanvig, “Why Should Inquiring Minds Want to Know?”)
  43. § 38 Giving up on (exact) truth (Elgin, “True Enough”)
  44. § 39 Naturalized epistemology advertised (Quine, “Epistemology Naturalized”)
  45. § 40 Naturalized epistemology criticized (Kim, “What is ‘Naturalized Epistemology’?”)
  46. § 41 Naturalized epistemology radicalized (Antony, “Quine as Feminist”)
  47. § 42 A apriori justification and unrevisability (Putnam, “There is at Least One A Priori Truth”)
  48. § 43 A priori justification and revisability (Casullo, “Revisability, Reliabilism, and A Priori Knowledge”)
  49. § 44 Philosophical method and empirical science (Bealer, “A Priori Knowledge and the Scope of Philosophy”)
  50. § 45 Experimental epistemology (Weinberg, Nichols and Stich, “Normativity and Epistemic Intuitions”)
  51. § 46 Natural kinds, intuitions and method in epistemology (Kornblith, “Investigating Knowledge Itself”)
  52. § 47 Contextualism and skeptical puzzles (DeRose, “Solving the Skeptical Problem”)
  53. § 48 Contextualism and infallibilist intuitions (Lewis, “Elusive Knowledge”)
  54. § 49 Contextualism and intuitional instability (Cohen, “Contextualist Solutions to Epistemological Problems”)
  55. § 50 Knowledge and action (Stanley, “Knowledge and Practical Interests, Selections”)
  56. § 51 Rationality and action (Fantl and McGrath, “Evidence, Pragmatics, and Justification”)
  57. § 52 One invariantist’s scorecard (Hawthorne, “Sensitive Moderate Invariantism”)
  58. § 53 A relativist theory of knowledge attributions (MacFarlane, “The Assessment Sensitivity of Knowledge Attributions”)
  59. § 54 Rationality and trust (Baker, “Trust and Rationality”)
  60. § 55 Testimony and gullibility (Fricker, “Against Gullibility”)
  61. § 56 Some reflections on how epistemic sources work (Burge, “Content Preservation”)
  62. § 57 Testimony and knowledge (Lackey, “Testimonial Knowledge and Transmission”)
  63. § 58 Memory and knowledge (Huemer, “The Problem of Memory Knowledge”)
  64. § 59 Perception and knowledge (McDowell, “Criteria, Defeasibility, and Knowledge”)
  65. § 60 Skills and knowledge (Reynolds, “Knowing How to Believe with Justification”)
  66. Index