Fred Dretske obituary US philosopher whose background in engineering provided a model for his carefully crafted theories of epistemology Fred Dretske argued that justificatory beliefs have to provide conclusive reasons for the beliefs they justify. His first degree was in electrical engineering: in his subsequent work, he liked to use examples from engineering, and constructed theories with many well-designed parts carefully fitted together to form functioning wholes. He belonged to the naturalist tradition, discounting explanations that extend beyond the laws of nature to the supernatural or spiritual. Although he did not suppose that philosophy and science were exactly the same enterprise, he did think that philosophical theories should be scientifically respectable. And much of his work sought to show how elements of the mind are natural phenomena that can be understood in scientifically acceptable terms.
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Precisely what is meant by the claim that knowledge is closed under entailment? One response is that the following straight principle of closure of knowledge under entailment is true: SP If person S knows p, and p entails q, then S knows q. The conditional involved in the straight principle might be the material conditional, the subjunctive conditional, or entailment, yielding three possibilities, each stronger than the one before: SP1 S knows p and p entails q only if S knows q.
SP2 If S were to know something, p, that entailed q, S would know q. SP3 It is necessarily the case that: S knows p and p entails q only if S knows q. However, each version of the straight principle is false, since we can know one thing, p, but fail to see that p entails q, or for some other reason fail to believe q. Since knowledge entails belief according to nearly all theorists , we fail to know q. A less obvious worry is that we might reason badly in coming to believe that p entails q.
Perhaps we think that p entails q because we think everything entails everything, or because we have a warm tingly feeling between our toes.
Hawthorne raises the possibility that, in the course of grasping that p entails q, S will cease to know p. He also notes that SP1 is defensible on the deviant assumption that a thought, p, is equivalent to another, q, if p and q hold in all of the same possible worlds.
Suppose p entails q. Then p is equivalent to the conjunction of p and q, and so the thought p is identical to the thought p and q.
Hence in knowing p S knows p and q. The straight principle needs qualifying, but this should not concern us so long as the qualifications are natural given the idea we are trying to capture, namely, that we can extend our knowledge by recognizing, and accepting thereby, things that follow from something that we know. The qualifications embedded in the following principle construed as a material conditional seem natural enough: K If, while knowing p, S believes q because S knows that p entails q, then S knows q.
As Williamson notes, the idea that we can extend our knowledge by applying deduction to what we know supports a closure principle that is stronger than K. It is a principle that says we know things we believe on the grounds that they are jointly implied by several separate known items.
Suppose I know Mary is tall and I know Mary is left handed. K does not authorize my putting these two pieces of knowledge together so as to know that Mary is tall and left handed. But the following generalized closure principle covers deductions involving separate known items: GK If, while knowing various propositions, S believes p because S knows that they entail p, then S knows p. However, it is far from clear that one may competently deduce q from p without relying on any knowledge aside from p.
Proponents of closure might accept both K and GK, perhaps further qualified in natural ways but they might not: see the concerns about justification closure raised in section 6.
They reject any closure principle, no matter how narrowly restricted, that warrants our knowing that skeptical hypotheses e. In addition to rejecting K and GK, they deny knowledge closure across instantiation and simplification, but not across equivalence Nozick — : KI If, while knowing that all things are F, S believes a particular thing a is F because S knows it is entailed by the fact that all things are F, then S knows a is F.
KS If, while knowing p and q, S believes q because S knows that q is entailed by p and q, then S knows q. Let us turn to their arguments.
The Argument From the Analysis of Knowledge The argument from the analysis of knowledge says that the correct account of knowledge leads to K failure. We can distinguish two versions. According to the first version, K fails because knowledge requires belief tracking. We can skip the defense, which consists largely in showing that tracking does a better job than competitors in dealing with our epistemic intuitions about cases of purported knowledge.
We may also simplify the analyses. According to Nozick, to know p is, very roughly and ignoring his thoroughly discredited fourth condition for knowledge, criticized, e. That is, in the close worlds to the actual world in which not-p holds, S does not believe p. BT requires that in all nearby not-p worlds S fails to believe p.
The semantics of subjunctive conditionals is clarified in Stalnaker , Lewis , and modified by Nozick note 8. That is, in the close worlds to the actual world in which not-p holds, R does not. When R meets this condition, Dretske says R is a conclusive reason for believing p. Dretske pointed out , n. I also notice that it is red. Because I have barn-before-me percepts, I believe barn: the object in front of me is a ordinary barn the example is attributed to Ginet in Goldman Our intuitions suggest that I fail to know barn.
And so say BT and CR. But now suppose that the neighborhood has no fake red barns; the only fake barns are blue. Call this the red barn case. Let R, my basis for belief, be the fact that I have red-barn percepts. If no barn were there, R would fail to hold, so I know a barn is there. Further, if no red barn were there, R would still fail to hold, so I know a red barn is there. So Dretske can avoid the objectionable juxtaposition.
First, Dretske himself accepted juxtapositions of knowledge and ignorance that are at least equally bizarre, as we shall see. Second, Nozick avoided the very juxtaposition Dretske discussed by restating his account to make reference to the methods via which we come to believe things Hawthorne If no red barn were there I would believe neither that there was a barn, nor that there was a red barn, via red-barn percepts. Third, the red barn case is one about which intuitions will vary.
The tracking accounts permit counterexamples to K. It occurs to you that zeb entails not-mule, it is not the case that the animal in the cage is a cleverly disguised mule rather than a zebra. You then believe not-mule by deducing it from zeb. What do you know?
You know zeb, since, if zeb were false, you would not have zebra-in-a-cage visual percepts; instead, you would have empty-cage percepts, or aardvark-in-a-cage percepts, or the like. Do you know not-mule? If not-mule were false, you would still have zebra-in-a-cage visual percepts and you would still believe zeb, and you would still believe not-mule by deducing it from zeb.
So you do not know not-mule. But notice that we have: You know zeb You believe not-mule by recognizing that zeb entails not-mule You do not know not-mule. In view of a — c , we have a counterexample to K, which entails that if a you know zeb, and b you believe not-mule by recognizing that zeb entails not-mule, then you do know not-mule, contrary to c.
Having rejected K, and denying that we know things like not-mule, Nozick also had to deny closure across simplification. In response to this first version of the argument from the analysis of knowledge, some theorists e. To show there are no compelling reasons to abandon K, theorists have provided accounts of knowledge that a handle our intuitions at least as successfully as the tracking analyses and yet b underwrite K.
One way to do this is to weaken the tracking analysis so that we know things that we track or that we believe because we know that they follow from things that we track this sort of option has been turned against Nozick by various theorists; Roush defends it in , 41— Another approach is as follows.
SI requires that p be true in the nearby R worlds. When R meets this condition, let us say that R is a safe indicator that p is true. Different versions of the safety condition have been defended; see, for example, Luper ; Sosa , , , ; Williamson ; and Pritchard SI is the contraposition of CR, but the contraposition of a subjunctive conditional is not equivalent to the original.
Let us suppose without argument that SI handles cases of knowledge and ignorance as intuitively as CR. Why say SI underwrites K? Put another way, the point is that the following reasoning is valid being an instance of strengthening the consequence : If R held, p would be true i. S is also in a position to know q on the basis of the conjunction of R together with the fact that p entails q.
Thus if S knows p on some basis R, and believes q on the basis of R on which p rests together with the fact that p entails q, then S knows q. Again: if S knows p on the basis of R , and S believes q by recognizing that p entails q so that S believe q on the basis of R, on which p rests, together with the fact that p entails q , then S knows q on the basis of R and the fact that p entails q , as K requires.
Having based your belief zeb on your zebra-in-the-cage percepts, you know zeb according to SI: given your circumstances, if you had those percepts, zeb would be true.
Moreover, when you believe not-mule by first believing zeb on the basis of your zebra-in-the-cage percepts then deducing not-mule from zeb, you know not-mule according to SI: if you had those percepts not only would zeb hold, so would its consequence not-mule. For example, at one point Ernest Sosa discussed the following version of the condition: If S were to believe p, p would be true.
The point can be illustrated with a version of the red barn case. Suppose that on the basis of my red-barn percepts I believe red barn: there is a red barn in front of me.
Suppose, too, that there is indeed a red barn there. However you guessed it many fake barns are scattered through the neighborhood, all of which are blue, not red. In the close worlds in which I believe red barn, I am correct, so I meet the requisite condition for knowing red barn, which is that my believing red barn safely indicates its own truth.
Now, red barn entails barn: there is a barn in front of me. But, according to the view on offer, the requisite condition for knowing barn is not that my belief red barn safely indicates that barn holds. What is required instead is that my belief barn safely indicates its own truth. Assuming that I would believe barn if I saw one of the blue fakes, then my belief barn does not safely indicate its truth.
To pick up the thread again: now, K fails if knowledge entails CR but not if knowledge entails SI, but it may not be possible to underwrite K merely by replacing CR with SI, since some other condition for knowledge might block closure. As we have understood safety, we can believe things on safe grounds without knowing them. An obvious example is any necessary truth: because it holds in all possible worlds we can safely believe it for any reason. For another example, recall the red barn case discussed earlier: despite the many fake blue barns in the neighborhood, my red-barn percepts are safe indicators that the object in front of me is a barn and that it is a red barn, so no objectionable juxtaposition such as I know there is a red barn but not there is a barn occurs, but some theorists will insist that, in the circumstances sketched, I know neither that the object is a barn nor that it is a red barn.
An analysis is a relevant alternatives account when it meets two conditions. According to the second condition, the analysis must say that knowing p requires ruling out all relevant alternatives to p but not all alternatives to p.
It says an alternative A is ruled out on the basis of R if and only if the following condition is met: CRR were A to hold R would not hold. So the tracking account is a relevant alternatives approach. But why say that relevant alternatives accounts of knowledge are in tension with K?
Alvin Goldman, in developing a causal account of knowledge, constructs a situation in which S is said to know that a nearby mountain I will call it M erupted many years ago. He knows this on the basis of the presence of solidified lava throughout the countryside surrounding the mountain. I do not 4 The wording of 2 will sometimes have to be adjusted to suit the particular instantiation in question. The chief factors determining this adjustment are the relative temporal locations of R, P and the time of utterance and also the causal connections, if any, which are believed to hold between R and P. The particular wording I have given 2 is most appropriate when P is some state of affairs antecedent to or contemporaneous with both R and the time of utterance.
Dretske, Fred. Conclusive Reasons
Precisely what is meant by the claim that knowledge is closed under entailment? One response is that the following straight principle of closure of knowledge under entailment is true: SP If person S knows p, and p entails q, then S knows q. The conditional involved in the straight principle might be the material conditional, the subjunctive conditional, or entailment, yielding three possibilities, each stronger than the one before: SP1 S knows p and p entails q only if S knows q. SP2 If S were to know something, p, that entailed q, S would know q. SP3 It is necessarily the case that: S knows p and p entails q only if S knows q.
DRETSKE CONCLUSIVE REASONS PDF
Dojar There is a substantial literature on the transmissibility of evidence and its failure; see, for example, Crispin Wright and Martin Davies It is a principle that says we know things we believe on the grounds that they are jointly implied conclsive several separate known items. Broad Michael Burke C. If, while knowing pS believes q because S knows that p entails qthen S knows q. According to Dretske First, propositional justification does not entail belief.