R. Nozick - Knowledge and Scepticism.pdf

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Knowledge and Scepticism
ROBERT NOZICK
Robert Nozick (1938-2002) was Pellegrino University Professor at Harvard
University. His early book in political theory, Anarchy, State, and Utopia, was
very influential, and he followed it with Philosophical Explanations, The
Examined Life, The Nature of Rationality, Socratic Puzzles, and Invariances: The
Structure of the Objective World.
___________________________________
Reprinted from Robert Nozick. Philosophical Explanations (Cambridge, Mass.:
Harvard University Press, 1981), by permission of the publisher.
You think you are seeing these words, but could you not be hallucinating or
dreaming or having your brain stimulated to give you the experience of seeing
these marks on paper although no such thing is before you? More extremely, could
you not be floating in a tank while super-psychologists stimulate your brain
electrochemically to produce exactly the same experiences as you are now having,
or even to produce the whole sequence of experiences you have had in your
lifetime thus far? If one of these other things was happening, your experience
would be exactly the same as it now is. So how can you know none of them is
happening? Yet if you do not know these possibilities don't hold, how can you
know you are reading this book now? If you do not know you haven't always been
floating in the tank at the mercy of the psychologists, how can you know
anything-what your name is, who your parents were, where you come from?
The sceptic argues that we do not know what we think we do. Even when he leaves
us unconverted, he leaves us confused. Granting that we do know, how can we?
Given these other possibilities he poses, how is knowledge possible? In
answering this question. we do not seek to convince the sceptic, but rather to
formulate hypotheses about knowledge and our connection to facts that show how
knowledge can exist even given the sceptic's possibilities. These hypotheses
must reconcile our belief that we know things with our belief that the sceptical
possibilities are logical possibilities.
The sceptical possibilities, and the threats they pose to our knowledge, depend
upon our knowing things (if we do) mediately, through or by way of something
else. Our thinking or believing that some fact p holds is connected somehow to
the fact that p, but is not itself identical with that fact. Intermediate links
establish the connection. This leaves room for the possibility of these
intermediate stages holding and producing our belief that p, without the fact
that p being at the other end. The intermediate stages arise in a completely
different manner, one not involving the fact that p although giving rise to the
appearance that p holds true.
Are the sceptic's possibilities indeed logically possible? Imagine reading a
science fiction story in which someone is raised from birth floating in a tank
with psychologists stimulating his brain. The story could go on to tell of the
person's reactions when he is brought out of the tank, of how the psychologists
convince him of what had been happening to him, or how they fail to do so. This
story is coherent, there is nothing self-contradictory or otherwise impossible
about it. Nor is there anything incoherent in imagining that you are now in this
situation, at a time before being taken out of the tank. To ease the transition
out, to prepare the way, perhaps the psychologists will give the person in the
tank thoughts of whether floating in the tank is possible, or the experience of
reading a book that discusses this possibility, even one that discusses their
easing his transition. (Free will presents no insuperable problem for this
possibility. Perhaps the psychologists caused all your experiences of choice,
including the feeling of freely choosing; or perhaps you do freely choose to act
while they, cutting the effector circuit, continue the scenario from there.)
Some philosophers have attempted to demonstrate there is no such coherent
possibility of this sort.' However, for any reasoning that purports to show this
sceptical possibility cannot occur, we can imagine the psychologists of our
science fiction story feeding it to their tank-subject, along with the
(inaccurate) feeling that the reasoning is cogent. So how much trust can be
placed in the apparent cogency of an argument to show the sceptical possibility
isn't coherent? The sceptic's possibility is a logically coherent one, in
tension with the existence of (almost all) knowledge; so we seek a hypothesis to
explain how, even given the sceptic's possibilities, knowledge is possible. We
may worry that such explanatory hypotheses are ad hoc, but this worry will
lessen if they yield other facts as well, fit in with other things we believe,
and so forth. Indeed, the theory of knowledge that follows was not developed in
order to explain how knowledge is possible. Rather, the motivation was external
to epistemology; only after the account of knowledge was developed for another
purpose did I notice its consequences for scepticism, for understanding how
knowledge is possible. So whatever other defects the explanation might have, it
can hardly be called ad hoc.
I. KNOWLEDGE
[Conditions for Knowledge]
Our task is to formulate further conditions to go alongside
(1) P is true
(2) 5 believes that p.
We would like each condition to be necessary for knowledge, so any case that
fails to satisfy it will not be an instance of knowledge. Furthermore, we would
like the conditions to be jointly sufficient for knowledge, so any case that
satisfies all of them will be an instance of knowledge. We first shall formulate
conditions that seem to handle ordinary cases correctly, classifying as
knowledge cases which are knowledge, and as non-knowledge cases which are not;
then we shall check to see how these conditions handle some difficult cases
discussed in the literature.
One plausible suggestion is causal, something like: the fact that p (partially)
causes S to believe that p, that is, (2) because (1). But this provides an
inhospitable environment for mathematical and ethical knowledge; also there are
well-known difficulties in specifying the type of causal connection. If someone
floating in a tank oblivious to everything around him is given (by direct
electrical and chemical stimulation of the brain) the belief that he is floating
in a tank with his brain being stimulated, then even though that fact is part of
the cause of his belief, still he does not know that it is true.
Let us consider a different third condition:
(3) If p were not true, 5 would not believe that p.
Throughout this work, let us write the subjunctive "if-then" by an arrow, and
the negation of a sentence by prefacing "not-" to it. The above condition thus
is rewritten as:
(3) not-p → not-(5 believes that p).
This subjunctive condition is not unrelated to the causal condition. Often when
the fact that p (partially) causes someone to believe that p, the fact also will
be causally necessary for his having the belief without the cause, the effect
would not occur. In that case, the subjunctive condition (3) also will be
satisfied. Yet this condition is not equivalent to the causal condition. For the
causal condition will be satisfied in cases of causal overdetermination, where
either two sufficient causes of the effect actually operate, or a back-up cause
(of the same effect) would operate if the first one didn't; whereas the
subjunctive condition need not hold for these cases.2 When the two conditions do
agree, causality indicates knowledge because it acts in a manner that makes the
subjunctive (3) true.
The subjunctive condition (3) serves to exclude cases of the sort first
described by Edward Gettier, such as the following. Two other people are in my
office and I am justified on the basis of much evidence in believing the first
owns a Ford car; though he (now) does not, the second person (a stranger to me)
owns one. I believe truly and justifiably that someone (or other) in my office
owns a Ford car, but I do not know someone does. Concluded Gettier, knowledge is
not simply justified true belief.
The following subjunctive, which specifies condition (3) for this Gettier case,
is not satisfied: if no one in my office owned a Ford car, I wouldn't believe
that someone did. The situation that would obtain if no one in my office owned a
Ford is one where the stranger does not (or where he is not in the office); and
in that situation I still would believe, as before, that someone in my office
does own a Ford, namely, the first person. So the subjunctive condition (3)
excludes this Gettier case as a case of knowledge.
The subjunctive condition is powerful and intuitive, not so easy to satisfy, yet
not so powerful as to rule out everything as an instance of knowledge. A
subjunctive conditional "if p were true, q would be true," p → q, does not say
that p entails q or that it is logically impossible that p yet not-q. It says
that in the situation that would obtain if p were true, q also would be true.
This point is brought out especially clearly in recent "possible-worlds"
accounts of subjunctives: the subjunctive is true when (roughly) in all those
worlds in which p holds true that are closest to the actual world, q also is
true. (Examine those worlds in which p holds true closest to the actual world,
and see if q holds true in all these.) Whether or not q is true in p worlds that
are still farther away from the actual world is irrelevant to the truth of the
subjunctive. I do not mean to endorse any particular possible-worlds account of
subjunctives, nor am I committed to this type of account.3 I sometimes shall use
it, though, when it illustrates points in an especially clear way.
The subjunctive condition (3) also handles nicely cases that cause difficulties
for the view that you know that p when you can rule out the relevant
alternatives to p in the context. For, as Gail Stine writes, "what makes an
alternative relevant in one context and not another? . . . if on the basis of
visual appearances obtained under optimum conditions while driving through the
countryside Henry identifies an object as a barn, normally we say that Henry
knows that it is a barn. Let us suppose, however, that unknown to Henry, the
region is full of expertly made papier-mache facsimiles of barns. In that case,
we would not say that Henry knows that the object is a barn, unless he has
evidence against it being a papier-mache facsimile, which is now a relevant
alternative. So much is clear, but what if no such facsimiles exist in Henry's
surroundings, although they once did? Are either of these circumstances
sufficient to make the hypothesis (that it's a papier-mache object) relevant?
Probably not, but the situation is not so clear:”4 Let p be the statement that
the object in the field is a (real) barn, and q the one that the object in the
field is a papier-mache barn. When papier-mache barns are scattered through the
area, if p were false, q would be true or might be. Since in this case (we are
supposing) the person still would believe p, the subjunctive
(3) not-p → not-(S believes that p)
is not satisfied, and so he doesn't know that p. However, when papier-mache
barns are or were scattered around another country, even if p were false q
wouldn't be true, and so (for all we have been told) the person may well know
that p. A hypothesis q contrary to p clearly is relevant when if p weren't true,
q would be true; when not-p → q. It clearly is irrelevant when if p weren't
true, q also would not be true; when not-p → not-q. The remaining possibility
is that neither of these opposed subjunctives holds; q might (or might not) be
true if p weren't true. In this case, q also will be relevant, according to an
account of knowledge incorporating condition (3) and treating subjunctives along
the lines sketched above. Thus, condition (3) handles cases that befuddle the
"relevant alternatives" account; though that account can adopt the above
subjunctive criterion for when an alternative is relevant, it then becomes
merely an alternate and longer way of stating condition (3).
Despite the power and intuitive force of the condition that if p weren't true
the person would not believe it, this condition does not (in conjunction with
the first two conditions) rule out every problem case. There remains, for
example, the case of the person in the tank who is brought to believe, by direct
electrical and chemical stimulation of his brain, that he is in the tank and is
being brought to believe things in this way; he does not know this is true.
However, the subjunctive condition is satisfied: if he weren't floating in the
tank, he wouldn't believe he was.
The person in the tank does not know he is there, because his belief is not
sensitive to the truth. Although it is caused by the fact that is its content,
it is not sensitive to that fact. The operators of the tank could have produced
any belief, including the false belief that he wasn't in the tank; if they had,
he would have believed that. Perfect sensitivity would involve beliefs and facts
varying together. We already have one portion of that variation, subjunctively
at least: if p were false he wouldn't believe it. This sensitivity as specified
by a subjunctive does not have the belief vary with the truth or falsity of p in
all possible situations, merely in the ones that would or might obtain if p were
false. The subjunctive condition
(3) not-p → not-(S believes that p)
tells us only half the story about how his belief is sensitive to the truth-
value of p. It tells us how his belief state is sensitive to p's falsity, but
not how it is sensitive to p's truth; it tells us what his belief state would be
if p were false, but not what it would be if p were true. To be sure, conditions
(1) and (2) tell us that p is true and he does believe it, but it does not
follow that his believing p is sensitive to p's being true. This additional
sensitivity is given to us by a further subjunctive: if p were true, he would
believe it.
(4) p → S believes that p.
Not only is p true and S believes it, but if it were true he would believe it.
Compare: not only was the photon emitted and did it go to the left, but (it was
then true that): if it were emitted it would go to the left. The truth of
antecedent and consequent is not alone sufficient for the truth of a
subjunctive; (4) says more than (1) and (2). Thus, we presuppose some (or
another) suitable account of subjunctives. According to the suggestion
tentatively made above, (4) holds true if not only does he actually truly
believe p, but in the 'close' worlds where p is true, he also believes it. He
believes that p for some distance out in the p . neighbourhood of the actual
world; similarly, condition (3) speaks not of the whole not-p neighbourhood of
the actual world, but only of the first portion of it. (1f, as is likely, these
explanations do not help, please use your own intuitive understanding of the
subjunctives (3) and (4).)
The person in the tank does not satisfy the subjunctive condition (4). Imagine
as actual a world in which he is in the tank and is stimulated to believe he is,
and consider what subjunctives are true in that world. It is not true of him
there that if he were in the tank he would believe it; for in the close world
(or situation) to his own where he is in the tank but they don't give him the
belief that he is (much less instill the belief that he isn't) he doesn't
believe he is in the tank. Of the person actually in the tank and believing it,
it is not true to make the further statement that if he were in the tank he
would believe it--so he does not know he is in the tank.
The subjunctive condition (4) also handles a case presented by Gilbert Harman.8
The dictator of a country is killed; in their first edition, newspapers print
the story, but later all the country's newspapers and other media deny the
story, falsely. Everyone who encounters the denial believes it (or does not know
what to believe and so suspends judgement). Only one person in the country fails
to hear any denial and he continues to believe the truth. He satisfies
conditions (1)-(3) (and the causal condition about belief) yet we are reluctant
to say he knows the truth. The reason is that if he had heard the denials, he
too would have believed them, just like everyone else. His belief is not
sensitively tuned to the truth, he doesn't satisfy the condition that if it were
true he would believe it. Condition (4) is not satisfied.
There is a pleasing symmetry about how this account of knowledge relates
conditions (3) and (4), and connects them to the first two conditions. The
account has the following form.
(1)
(2)

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