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Common Sense and the Self-Refutation of Skepticism


I begin then, with my list of truisms, every one of whichÉ
I know, with certainty, to be true."
--G.E. Moore, "A Defence of Common Sense" 

 "Russell's view that I do not now for certain that this is
a pencil or that you are conscious rests, if I am right, on
four assumptions. And what I can't help asking myself is
this: Is it, in fact, as certain that all these four
assumptions are true, as that I do know that this is a
pencil and that you are conscious? I cannot help answering:
It seems to me more certain that I do know that this is a
pencil and that you are conscious, than that any single one
of these four assumptions is true, let alone all four. Nay
more: I do not think it is rational to be as certain of any
one of these four propositions, as of the proposition that
I do know that this is a pencil."
 --G.E. Moore, "Four Forms of Skepticism"
Bryan Caplan Bojana Paper #4, Topic #3 April, 1993 1.
Introduction David Hume, the most famous of all skeptical
philosophers, is almost equally famous for his admission
that neither he nor anyone else could integrate skepticism
into daily life: "[S]ince reason is incapable of dispelling
these clouds, nature herself suffices to that purpose. I
dine, I play a game of backgammon, I converse and am merry
with my friends; and when after three or four hours'
amusement, I would return to these speculations, they
appear so cold and strained and ridiculous that I cannot
find in my heart to enter into them any farther. Here then
I find myself absolutely and necessarily determined to live
and talk and act like other people in the common affairs of
life."1 While Hume thought that this just further
demonstrated the weakness of human reason, I think that we
can use this admission to build a general refutation of
skepticism. Accordingly, this paper will first explain my
general strategy against skepticism; second, answer typical
objections to my view; and third, briefly comment on the
central error of skepticism. 2. The General Strategy All
rational arguments -- in philosophy as well as other fields
-- reason from premises to conclusions. If the premises are
true, then so are the conclusions; if the conclusions are
false, then at least one of the premises must be false.
This is just elementary logic, but pay close attention to
this structure: Arguments link premises and conclusions.
Suppose then that something produces an argument such that
the conclusions follow from the premises. Must we, on pain
of irrationality, accept the conclusion? Not at all; it
always remains open to us to deny the premises. Of course,
we could admit the premises and accept the conclusion. But
reason in general doesn't require it. To reach true
conclusions we need more than valid arguments; we also need
to figure out whether to admit the premises and hence the
conclusion, or deny the conclusion and hence the premises.
How should we rationally make this choice? Oftentimes, we
can use other arguments to attack the same problem from a
different angle. But in philosophical arguments, we
frequently find that the whole of our knowledge, or very
large pieces of it, are in question. And in any case, it
couldn't generally be the case that we resolve the conflict
between premises and conclusions by bringing in other
arguments, since that would lead to an infinite regress.
The problem of plausible premises coupled with implausible
conclusions seems intractable. However, in my previous
papers 2 I pointed to our faculty of judgment, which is
variously called intellect, reason, and intuition.
I argued that by honestly and thoughtfully applying our
intellect to certain propositions, we could immediately see
their truth -- even if (contra Hume) the opposite is
conceivable and implies no self- contradiction. Thus, I
said that we come to learn the law of cause- and-effect not
by experience alone (which, as Hume showed, would be
circular), nor by scrutinizing the definitions of the terms
(which would not reveal the truth or falsity of the law),
but by carefully focusing our intellects on the law and
thinking about it until its truth becomes evident. We
establish the truth of many propositions this way: logical
laws and mathematics, for example. I propose to handle the
conflict between premises and conclusions in precisely the
same way. Suppose that a set of premises implies a
conclusion. The premises seem evident; but the conclusion
doesn't. Maybe the conclusion is false, and we were too
quick to accept the premises; but maybe the premises are
true, and prejudice alone prevents us from accepting the
conclusion. As before, apply your faculty of judgment, your
intellect, to the problem. Try to think about the two sets
of propositions as honestly and carefully as you can, until
you figure out which is more likely (or perhaps certain) to
be true.3 To give an example from my own field, the French
economist Frederic Bastiat noted that many people thought
that labor-saving machinery was bad because it destroyed
jobs. He suggested that it would therefore be a wise policy
to destroy all machinery, and thereby create even more
jobs. Bastiat presents a premise that many people believe,
coupled with an implication of it that no one believes. But
how should we choose rationally? Consider the premise and
the conclusion and decide whether it makes more sense for
the conclusion to be true or the premise to be false. It
turns out that the conclusion is so absurd that both it and
the premise must be wrong. How does this relate to
skepticism? Every valid skeptical argument, like all valid
arguments, gives us two choices: either reject the premises
or accept the conclusion. For example, Hume shows that the
distinction between matters of fact and relations of ideas
implies skepticism about induction. This doesn't prove that
induction isn't valid. It just shows that either we must
reject the distinction or become skeptics about induction.
So too with Descartes: either we must reject his theory of
perception or become skeptics about the external world. At
this point, I return to the observation that skeptical
arguments never "inspire conviction." Humean philosophers
and scientists don't abandon inductive arguments. Hume
himself admitted that he couldn't believe his conclusions
for more than a few moments at a time. What does this show?
It shows that even radical skeptics seriously doubt their
conclusions. And often their doubt is not a mere feeling of
unease, but serious intellectual doubt.
Thus, skeptical scientists find themselves unable to
believe Hume's critique of induction as they unemotionally
make scientific arguments. The doubt is intellectual,
spurred by the inability to rationally forego inductive
argument. And what about the premises?
They would have to be mightily evident to retain belief
even after they yielded such counterintuitive conclusions.
Yet they are not at all evident; they are fairly abstract
and each can be (and has been) reasonably criticized.
From these two observations I draw this conclusion:
Skepticism is irrational because it always involves
rejecting an obvious conclusion in favor of a highly
dubious premise. That inductive arguments are valid is
quite evident; the distinction between matters of fact and
relations of ideas isn't. The existence of the external
world is evident; the representationalist theory of
perception isn't. Of course, taken by themselves, it would
take some effort to refute the latter two views. But when
they imply manifestly false propositions, we should
immediately conclude that the premises must be false.
Indeed, this is one of the best tests of dubious premises:
see whether they imply anything absurd. If they do, then
the premises should be rejected. To do otherwise is to
select a less evident over a more evident conclusion.
Another fact to consider is that all philosophical premises
are difficult and abstract. They may seem obvious after a
while, but nevertheless, they remain difficult and
abstract. It would be easy to err in this area: for
naturally, the likelihood of error grows with the
difficulty and abstractness of the subject matter. In
contrast, the propositions of common sense are indeed
simple and easy. Almost everyone understands them -- not
just brilliant philosophers. Given this contrast - between
the simplicity of common sense and the difficulty of
philosophy - where are we more likely to mistake a
falsehood for the truth?
Let me state the argument another way. Common sense tells
us, among other things, that induction is valid and that
there is an external world. These propositions are simple
and evident. Now in order to argue against them, one would
naturally have to begin with premises that are even more
evident; for it would be impossible to refute a more
evident principle with a less evident one. After all, if a
less evident principle conflicts with a more evident one,
then it is the less evident one that must go. And yet,
there are no premises more evident than the ones of common
sense -- especially not in philosophy, where the arguments
are difficult and abstract. If a philosophical theory
implies skepticism, we should take it as a reductio ad
absurdum, not a proof of skepticism. 3. Objections Answered
1. "You haven't argued for the truth of common sense;
you've just asserted it." The problem with this objection
is that it assumes that either one produces an argument or
makes an unjustified assertion. But these are not the only
possibilities. As I explained, it may be possible to
justify a claim not by arguing for it (which would lead to
an infinite regress), but rather by carefully and honestly
applying one's intellect to it until its truth becomes
immediately evident. As an example, consider mathematics.
You will notice that while mathematicians produce proofs,
they don't produce separate and additional proofs for each
step of the proof. Instead, they think about each step
carefully and honestly and decide whether it is valid; and
if it is, they make that step. And if someone else couldn't
see it, the mathematician wouldn't conclude that math was
unjustified; he would conclude that the person in question
wasn't very good at math. Using the intellect to evaluate
common sense is actually easier, since even Hume and other
skeptics demonstrate that they can't persistently deny
common sense, whereas there really are some people who
don't understand any mathematics. 2. "How do you handle
conflicts between common sense propositions?" The answer
is: by the same method as before. If there are two
conflicting claims of common sense, then we must once again
apply our intellect to the two claims, think about them as
carefully and honestly as we can, and then judge which is
more likely (or certain) to be true. For example, common
sense tells us both that the senses are valid and that the
sun revolves around the earth. So when scientists observed
that the earth revolves around the sun, philosophers should
have noted that a weaker common sense view (Ptolemaic
cosmology) had been refuted by a stronger common sense view
(the validity of the senses). Common sense wasn't refuted
at all. Rather, a more evident principle of common sense
was used to discredit a less evident one. Similarly, when
critical thinkers want to refute prejudices, they usually
show that popular beliefs have been refuted by careful
observation -- which is the common sense way to
double-check our views. 3. "Your view is actually a form of
pragmatism: it tells us to just accept 'common sense'
without justifying it." This complaint misunderstands me: I
am not saying that because skepticism isn't "practical" or
"useful" that it isn't true.
You can't believe whatever you feel like; you always have
to apply your intellect as honestly and carefully as you
can if you want to be right. We know that skepticism is
always wrong because when we compare it to common sense
views and think carefully and honestly, we can see that
common sense is always more likely (or certain).
And the fact that skeptics themselves habitually ignore
their own conclusions serves to bolster the claim that it
is always more likely that our initial premises are wrong
than that skepticism is true.
Since skeptics can't persistently hold their thesis without
implicitly assuming its negation, we have a good reason to
think that they should re-examine their premises and see if
they are as evident as they seem to think.4 4. "Your
'foundationalist' view actually helps skepticism, since it
is always conceivable that you're wrong and the world is
different than you think." This is another version of the
error I attacked in my first paper: the view that reason
can do nothing except uncover the presence or absence of
contradictions. If so, then one can always object to any
view that "Were it demonstratively false, it would imply a
contradiction, and could never be distinctly conceived by
the mind."5 But I don't concede this. Suppose that reason
does something other than merely pick out contradictions;
it can sometimes figure out that something is true just by
carefully thinking about it. In that case, one might say:
Of course, alternatives are "conceivable" but they are
nevertheless impossible.
It is conceivable that my reason is radically deficient,
but my very ability to grasp that claim shows the opposite.
(I.e., only if my reason worked could I know that it was
conceivable for my reason to be radically deficient).
Indeed, I could use my own anti-skeptical strategy to
refute this line of reasoning. The premise is that it is
always possible for me to be mistaken; the conclusion is
that the common sense correspondence theory of "absolute"
truth is untenable. Well, which is more evident after
careful and honest reflection: that it is always possible
for me to be mistaken, or that the common sense view of
truth is wrong? Surely the common sense view of truth is
more evident; indeed, it is arguably the strongest of all
common sense principles. Therefore, sometimes it is
impossible for me to be mistaken. If this seems arrogant,
consider an elementary principle of mathematics like
"1+1=2." While it is conceivable for me to err, it is
surely impossible that I could be wrong about "1+1=2." So
we have one example where error is conceivable yet
impossible. And if one -- why not others? And which others,
if not the principles of common sense? 4. Conclusion I
assume that many philosophers would find it hard to take
this blanket refutation of classic epistemological problems
seriously. But it follows from three simple premises: 1.
Presented with a valid argument, we must either accept the
premises and hence the conclusions, or else reject the
conclusions and therefore the premises. 2. It is irrational
to reject a more evident view in favor of a less evident
one. 3. The propositions of common sense are more evident
than any of the premises that imply skepticism (or, indeed,
any abstract philosophical premises). Premises #1 and #2
are completely evident. And while skeptics will surely say
that they deny premise #3, their practical inability to
actually be skeptics consistently should make us doubt
this. A proposition would have to be self-evident to
endlessly reassert itself in the minds of even committed
skeptics -- especially a brilliant skeptic like David Hume.
One would think that the very inability of skeptics to hold
their views consistently should have raised doubts in their
After all, if they can't even make sense of the world
without ignoring all of their philosophical views, then
they have a good reason to doubt those views. In general, I
can't understand why otherwise reasonable people don't
consider the simple possibility that their starting
premises were wrong. Such mistakes happen all the time; and
our best intellectual defense is to carefully check the
conclusions that they yield to make sure that they don't
contradict anything we know for certain -- most notably,
the claims of common sense.
Notes 1. Quoted in Frederick Copleston, A History of
Philosophy (New York: Doubleday, 1959), vol.5, pp.315-316.
2: Bryan Caplan, "An Enquiry Concerning Hume's
Misunderstanding" and idem, "Underived Knowledge: An Answer
to Skepticism about Induction and the External World." 3:
Admittedly, this advice is unsatisfying, since it offers no
general rule for correct thinking. But I see no
alternative; for suppose that someone suggested a rule. We
would then have to think about whether or not the rule were
correct; and to avoid an infinite regress, we would have to
admit that some rules could be judged directly and
immediately without recourse to further rules. So why not
just admit that it is possible to apply one's intellect
directly and immediately to individual propositions, which
is surely an easier task than judging vast classes of such
propositions? 4: While I am on the subject, let me sharply
distinguish my view from that of Nelson Goodman in his "The
New Riddle of Induction." Says Goodman, "A rule is amended
if it yields an inference we are unwilling to accept; an
inference is rejected if it violates a rule we are
unwilling to amend." (p.64) I, in contrast, say that we
should decide on the basis of what it more likely to be
The fact that I accept something isn't an argument for its
truth; people "accept" all sorts of false beliefs. But if
we think about something and see that it is true, we have a
justification for believing it. Goodman's error becomes
particularly evident when one realizes that different
people accept different things, but all of them can't be
right (as they could be by Goodman's criterion). 5: David
Hume, An Enquiry Concerning Human Understanding, pp.15-16.
Appendix (Not to be graded) If it is always more rational
to adhere to common sense than any theory in conflict with
common sense, what is left for philosophy to do? I can
think of at least three functions. First, philosophy can
develop positive theories about the world, knowledge, the
mind, and so on, since common sense rarely gives specific
answers to such questions. Common sense, for example, tells
us that we know things; but I doubt that common sense
recommends rationalism over empiricism or vice versa. The
only limitation my view adds is that all positive
philosophical theories must be consistent with common
sense. Second, philosophy can point out and resolve
inconsistencies -- real and apparent -- in common sense. A
good example of real conflict was that between the validity
of the senses and Ptolemaic cosmology -- which I discussed
above. To take an example of an apparent inconsistency, it
is hard to reconcile our common sense views that humans
have free will, that inanimate matter doesn't, and that
humans are composed of inanimate matter. At this point, a
philosopher might point out that the views aren't
necessarily inconsistent: an emergence theory of free will
can solve the problem. Third, philosophy can actively
search out the specific errors made by philosophical
theories in conflict with common sense.
Instead of trying to "refute" Hume or Descartes, for
example, philosophers would try to figure out where they
went wrong so that we can avoid similar errors in the
future. Their task would be easier than it is today,
because they would know before the fact that the arguments
were fallacious. 


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