Sensitivity, Indiscernibilityand Knowledge

Keith Lehrer

Sosa’s paper is a deeply insightful contribution to our under-standing of skeptical argument and the reply to it. I agree withSosa concerning his doubts about the epistemological significanceof contextualism. I have one further doubt about it beyond thosewhich he has raised. Many of the arguments to the effect that thecontext of utterance determines whether it is correct to say, “Sknows that p,” for various substitutions of “S” and “p” requirefurther argumentation to show that the contextual constraints aregenuinely semantic and not merely conversational constraints onthe appropriateness of saying, “S knows that p.” Many of theconstraints appear to me conversational constraints rather thansemantic indices. When a person says, “I know that p,” for exam-ple, he or she often gives their authority or word for the truth ofp in the context of the speech act, and whether this is appropri-ate depends on the context. When the context is one in which agreat deal hinges on whether or not p is true, one should be cau-tious about giving one’s word or authority for the truth of p. Con-sequently, it might be inappropriate to say, “I know that p,” insuch contexts even though one does know that p. I might, for

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example, know that a person has a certain telephone number butrefuse to say that I know this in a context in which a personwould be convicted of a serious crime were I to say that I knowthat was his or her telephone number. The reason I might refuseis that my memory for telephone numbers, though as good asmost, and, indeed, good enough for knowledge, is not good enoughfor me to give my word or authority for the truth of the claim insuch crucial circumstances. You might say that I do know, andcorrectly so, when I refuse to say so, because you know that Iknow the telephone number belongs to the person accused of thecrime. When you say that I know, you give your word, not mine,for the truth of the matter, and you, not I, are ready to do that.

I am not proposing this as a refined account of when it is ap-propriate to say in the first person or the third person that some-one knows that p. I only want to insist that the conversationalconstraints on when it is appropriate to say, “S knows that p,”are as complex as the constraints on whether it is appropriate togive ones word or authority for the truth of something.

To put the matter as a point of contention, I suggest that theindexicality of the word “short” is not a good model for under-standing the semantics of the word “know”. The use of the word“know” seems to me to be surrounded with a complex set of con-versational constraints which I do not pretend to have articulatedbut which have been discussed by Austin and Grice. I note thatSosa has not affirmed the correctness of the indexical account. Hehas only argued that it does not yield the epistemological conse-quences claimed for it. I agree with him and think it is excellentthat he has noted and explained so clearly why the view does nothave such consequences, but I should like to know whether hethinks that indexical account is true, false, or, whether he has noopinion in the matter.

Now I should like to turn to the important and insightful re-marks Sosa makes in the second section of his paper on the sen-sitivity condition and the safety condition. First of all, I agreewith Sosa that the tracking condition and the sensitivity condi-tion are not conditions of knowledge for exactly the reason hesays, namely, that they lead to the conclusion that we never knowthat we are not deceived about anything that we believe. It isimportant to notice that this consequence applies to garden vari-ety forms of deception, deceptions of memory, for example, aswell as the grand deceptions suffered by brains in vats and thosedeceived by demons. Take the clearest memory belief that youhave, the memory of who you are, in my case, that I am Keith

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Lehrer. Now I know that I am not deceived by my memory inbelieving this. Suppose, contrary to fact, that I were deceived bymy memory in believing this. I would believe that I was not de-ceived anyway. So the sensitivity condition is not satisfied. In otherwords, the tracking condition and the sensitivity condition bothhave the consequence that one can never know that one is notdeceived about anything in any way that would result in one be-lieving that one is not deceived.

Moreover, the safety condition is a much more plausible condi-tion. If I were to believe, as I do, that I am not deceived in be-lieving that I am Keith Lehrer, then I would not be deceived inbelieving this. However, the safety condition should, it seems tome, make explicit reference to the evidence on which I believewhat I do. That is, the sensitivity condition should be formulatedas follows: S’s belief that p is evidence is safe if and only if thefollowing: S has evidence e for believing that p and if S were tobelieve that p on the evidence e S has, then p. Sosa anticipatesthis sort of modification in his answer to an objection in which hesuggests that the belief be based on a reliable indication. I preferthe notion of being based on evidence to being based on a reli-able indication, but the motivation is similar, namely, that thetruth of p should be a result of the belief being based on theevidence one has rather than of the belief simpliciter. I shall ex-plain why I think that it is better to formulate the condition interms of evidence than in terms of reliable indicator below.

I also find plausible Sosa’s explanation of why we find the po-sition of the skeptic plausible, namely, that we confuse the sensi-tivity condition, which is incorrect, with the safety condition, whichis correct, because we invalidly contrapose the latter and confuseit with the former. The question that remains is whether thatprovides us with the explanation of why we find the skepticalposition that we do not know that we are not deceived in extraor-dinary ways, by being envatted, for example, plausible. There is,I suggest, more to the matter. There is a condition that has oftenbeen defended which might be called the indiscernibility condi-tion which leads to skepticism. Here is a formulation: IC. If thereis no discernible difference between that evidence I have for be-lieving p if p were true and the evidence I would have for believ-ing p if the denial of p were true, then I do not know that p onthe evidence I have for believing that p. With respect to the de-nial of skeptical hypotheses, for example, that I am not envatted,or that I am not deceived by the demon, IC leads to the conclu-sion that I do not know because the examples are constructed in

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such a way as to insure that there is no discernible differencebetween the evidence I would have for believing that p, that I amnot deceived, if that were true, and believing it, if the denial of itwere true. The deception is perfect after all. The point of thecondition is to require that the evidence we have that justifies usor simply converts belief into knowledge should enable us to dis-cern whether p is true or not. Thus, a defender of IC might ar-gue, contrary to Sosa, that the plausibility of the skeptical positionthat I do not know that I am not envatted, for example, does notdepend on accepting the sensitivity condition but rather on ac-cepting the indiscernibility condition.

There is a reply to this argument which is similar to what Sosasuggests, namely, that if I were to believe that I am not envattedon the evidence I have, then I would not be envatted. Thus, evi-dence can be reliable or worthy of our trust even though therewould no discernible difference in the evidence whether p is trueor or the denial of it is. The crux is that in the actual world,things being what they are, evidence is reliable or worthy of ourtrust, even if, in other worlds and other situations, it would notbe. In a world where we are not deceived by a demon and are notenvatted brains, the evidence we have is worthy of our trust. Thetrick of the skeptic is to ask us to consider remote worlds in whichthe skeptical hypotheses are true and the evidence we have is notreliable or worthy of trust and to conclude that it is not reliableor worthy of trust in the actual world. But the conclusion doesnot follow. To accept this solution is to reject IC on the groundsthat evidence that is reliable or worthy of our trust in the actualworld might not be so in more remote worlds. This means, how-ever, that the reliability or trustworthiness of evidence for a hy-pothesis does not hold across possible worlds. I should like toknow whether Sosa accepts this solution to the problem posedby IC.

Finally, Sosa uses reliability rather than trustworthiness as thebasis of a more refined account of the safety condition. This seemsto lead us in the wrong direction for familiar reasons, namely,that reliability may be epistemically opaque to the knower, thatis, the knower might not have any idea that the evidence or de-liverance is reliable. Moreover, the technical use of “reliable” iden-tifies reliability with general truth frequency, and evidence that isnot reliable in this sense may, nonetheless, be worthy of trust inspecial circumstances. Thus, it seems to me that it would be animprovement to refine that condition in terms of the normativenotion of the evidence or deliverance being worthy of the trust of

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the knower. Sosa may, of course, wish to insert a naturalized andexternal condition at this point in the analysis. I should like toknow why.

In summary, I think that Sosa is right to reject the sensitivitycondition and to advocate some version of the safety condition inplace of it as a necessary condition of knowledge. Moreover, Iagree that the confusion between the sensitivity condition andthe safety condition may well account for the tendency to acceptthe skeptical contention that we do not know that we are notenvatted or otherwise globally deceived. However, the indiscern-ibility condition is also a basis for concluding that we do notknow these things. The rejection of that condition is suggested bywhat Sosa has written but requires some extrapolation from it,namely, to the conditional that if we were to believe we are notenvatted on the evidence we have, then we would not be envat-ted, even though, were we envatted, we would have just sameevidence we have for believing we are not. I should like to know ifhe accepts that solution or some modification thereof to the prob-lem posed by the indiscernibility condition.

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