In 2008, Nicholas Evans, the author of the novel The Horse Whisperer, picked some wild mushrooms,sautéed them in butter, and served them to his family. They nearly died. The mushrooms were deadlywebcaps, which contain the potentially fatal toxin orellanine. Evans’s kidneys failed, and he laterreceived a kidney transplant from his daughter.
Evans did not know that the mushrooms were poisonous. If he had known that, he would never havecooked them. This illustrates one way in which knowledge is valuable. Lack of knowledge can haveserious, even fatal, consequences. Sometimes knowledge can save your life.
The kind of knowledge Evans lacked was propositional (or factual ) knowledge, where what follows theverb “to know” is a clause beginning with “that.” You know that the earth is round, and you know thatEvans wrote The Horse Whisperer. These clauses pick out what philosophers call propositions, thingsthat can be true or false. That the earth is round is a true proposition; that the earth is ﬂat is a falseproposition. This is why the kind of knowledge reported by a statement like “You know that the earth isround” is called propositional knowledge (and also sometimes knowledge-that). This is the topic of theselections that follow and is the main subject matter of the branch of philosophy called epistemology—derived from the Greek word episteme, meaning “knowledge.”
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Propositional knowledge is not the only kind of knowledge, as the variety of grammaticalconstructions using the verb “to know” indicates. For example, in one construction the verb is followedby a noun (or noun phrase) that typically picks out a person or a place. Nicholas Evans knows Scotland:he is quite familiar with that country, having picked mushrooms there. He also knows Robert Redford,the director and star of the movie based on Evans’s novel. We could paraphrase these claims by sayingthat Evans is acquainted with both Scotland and Redford. This sort of knowledge is accordingly calledacquaintance knowledge, or personal knowledge.
Propositional knowledge is not a kind of personal knowledge. Someone can know that Paris is thecapital of France without knowing Paris or France. What about the other way around? Could personalknowledge be a kind of propositional knowledge? That seems doubtful. If you read Michael Callan’slengthy Robert Redford: The Biography, you will acquire a lot of propositional knowledge aboutRedford but will not thereby know him. The case that propositional and acquaintance knowledge arequite diﬀerent can be strengthened by noting that many languages distinguish them using diﬀerentverbs, where English has only one. In French, for instance, connaître is used for acquaintanceknowledge and savoir for propositional knowledge.
There are other notable constructions using the verb “to know.” For example: Evans knows whereEdinburgh is, knows who inspired the main character in The Horse Whisperer, and knows which actordirected the movie. These constructions seem to say something about Evans’s propositionalknowledge. If Evans knows where Edinburgh is, then he knows that it is in Scotland, or south of theFirth of Forth, or some other salient fact about its location, and similarly for the other two examples.
There is another related construction that is less clearly propositional: Evans knows how to cookmushrooms, how to tie his shoes, and how to write best sellers. These are examples of knowledge-how,or procedural knowledge. Is procedural knowledge a kind of propositional knowledge? One might thinknot, on the ground that reading Julia Child’s Mastering the Art of French Cooking will give you lots ofpropositional knowledge about French cooking but is not guaranteed to prevent your souﬄés fromcollapsing. It is a controversial matter whether knowledge-how is a kind of propositional knowledge,although not one taken up in the selections.
Now that we have the relevant kind of knowledge clearly in view, the task is to say somethinginteresting about it. The traditional approach is to try to break knowledge down into its components,as one might study an engine by taking it apart.
One uncontroversial component of propositional knowledge is truth. When Evans picked the deadlywebcaps, he believed that they were harmless. Indeed, he presumably took himself to know that theywere harmless. “I know that these are harmless,” we can imagine him saying. But he did not know thatthe mushrooms were harmless, as they were not. You cannot know what is false: if S (a person) knows p,then p must be true.
Belief is a good candidate for another component of knowledge. If you know that the earth is round,then you will probably reply “The earth is round” if asked about its shape, be unconcerned when a shipdisappears over the horizon, and so forth. That is, you will give every impression that you believe thatthe earth is round. Although the belief component is not as uncontroversial as the truth component(the selection by Timothy Williamson discusses one objection), it is widely accepted. So let us assumethat if S knows p, then S must believe p.
So far, we have two components of knowledge: truth and belief. If S knows p, then it must be that (i)p is true, and (ii) S believes p. In other words, (i) and (ii) are necessary conditions for S to know p.
Necessary conditions need not also be suﬃcient conditions. Having four equal sides is a necessarycondition for being a square: it is impossible to be a square without having four equal sides. But it isnot a suﬃcient condition: having four equal sides does not guarantee being a square, as somerhomboids (which have four equal sides) are not squares. What about (i) and (ii)? Might they also be,taken together, a suﬃcient condition for knowledge? And if they are, then knowledge is just the twocomponents of belief and truth added together. That is: S knows p if and only if (i) p is true, and (ii) Sbelieves p.
However, as has been known since Plato’s time, belief and truth are not suﬃcient for knowledge.Suppose someone buys a ticket for the lottery convinced that he will win because his fortune teller toldhim so, and by a ﬂuke he does. He truly believed that he would win, but he did not know that he wouldwin. As Plato puts it, knowledge is not “correct opinion”; as a contemporary philosopher might say,knowledge cannot be “analyzed” as true belief. What might another component of knowledge be?
The lottery winner has no reasons or evidence for his true belief that he will win. That is, his belief isnot justiﬁed. Conversely, your true belief that the earth is round is justiﬁed—perhaps you read aboutits shape in a reliable textbook or a knowledgeable teacher told you that it is round. So this suggeststhat justiﬁcation is another component of knowledge. Like the belief component, the justiﬁcationcomponent is also widely accepted. So let us assume that if S knows p, then S must justiﬁably believe p.
Now we have three necessary conditions for S to know p. If S knows p, then it must be that (i) p istrue, (ii) S believes p, and (iii) S’s belief is justiﬁed. Might (i), (ii), and (iii) together be suﬃcient conditionsfor knowledge? And if they are, then knowledge is just the three components of belief, truth, andjustiﬁcation added together. That is: S knows p if and only if (i) p is true, (ii) S believes p, and (iii) S’sbelief is justiﬁed.
What else could knowledge be? There is no obvious fourth component, so the received view used tobe that knowledge simply is justiﬁed true belief.
All that changed with the publication in 1963 of Edmund Gettier’s “Is Justiﬁed True Belief Knowledge?”Gettier presents a series of examples in which someone has a justiﬁed true belief but apparently doesnot know. These Gettier cases are commonly taken to refute the claim that (i), (ii), and (iii) are suﬃcientfor S to know p.
Once you get the idea, Gettier cases are easy to construct. Here is one. Suppose that Evans believesthat the mushrooms are harmless because he consulted the authoritative Field Guide to EdibleMushrooms of Britain and Europe. Because of a printer’s error (most unlikely in a work of this kind),the photograph of deadly webcaps was captioned Ceps, a desirable type of edible mushroom. Evans’sfalse belief that the mushrooms are harmless is justiﬁed: he knows that past editions of the Field Guidewere accurate. Evans puts the mushrooms in a bag and takes them back to his kitchen. As far as heknows, these are his only mushrooms. He believes that the mushrooms in the bag are harmless andthat they are in his kitchen. Evans makes a trivial deductive inference from the premise that themushrooms in the bag in his kitchen are harmless, and he believes that there are some harmlessmushrooms in his kitchen. Since Evans is justiﬁed in believing the premise, and the conclusiondeductively follows from the premise, he is also justiﬁed in believing the conclusion. So Evans’s beliefthat there are some harmless mushrooms in his kitchen is justiﬁed. By luck, it is also true: Evans’s wifebought some mushrooms from the supermarket yesterday and put them in the refrigerator. Yet Evansdoes not know that there are some harmless mushrooms in his kitchen.
Gettier’s paper immediately created an industry tasked with ﬁnding a fourth component ofknowledge that, when added to truth, belief, and justiﬁcation, would result in a suﬃcient condition. Itproved very diﬃcult, and the consensus is that no such fourth component was ever found. (For moredetails, see this chapter’s “Reader’s Guide,” which follows the Gettier selection.)
Because of the apparent failure of this project (among other reasons), many philosophers havebecome skeptical that knowledge can be broken down into components. They accept that there are avariety of necessary conditions for S to know p, but they deny that these conditions are also jointlysuﬃcient for S to know p. Prominent among them is Timothy Williamson, who champions a“knowledge-ﬁrst” approach to epistemology. Knowledge, according to Williamson, cannot be analyzedas justiﬁed true belief plus some extra factor X; instead, knowledge should be taken as explanatorilyfundamental in its own right. Inquiry always proceeds with some things being taken for granted, notneeding a deﬁnition or analysis, and why can’t knowledge be one?
Even if knowledge is unanalyzable, that does not mean we cannot discover anything interestingabout it. Indeed, to say that truth, justiﬁcation, and belief are necessary conditions for knowledge isalready to say something interesting. And Williamson ﬁnds much more to say.
Many questions about knowledge remain. One is raised by Plato: Why is knowledge better than truebelief, or “correct opinion”? If Evans had known that the mushrooms were poisonous, then he wouldnot have cooked them. But he would not have cooked them if he had believed truly that they werepoisonous, whether or not he also knew that they were poisonous. Plato suggests a (somewhatmetaphorical) answer to that question: knowledge is “shackled” in the mind, whereas true belief has atendency to “scamper away and escape.” Williamson suggests a way to develop Plato’s answer. SupposeEvans has a mere true belief that the mushrooms in his possession are poisonous because someoverconﬁdent friend told him that all mushrooms in Scotland are poisonous. Evans might well learnlater that his friend is not to be trusted or that there are many edible mushrooms in Scotland. And if hedoes, he will give up his belief that the mushrooms are poisonous and perhaps will take them back tohis kitchen and start sautéing. By contrast, if he knows that the mushrooms are poisonous, he is muchless likely to change his mind.