© Michael Lacewing
Gettier and the analysis of knowledge
The tripartite definition of knowledge claims that knowledge is justified true belief. If you
have a justified true belief that p, you know that p; the conditions are sufficient for
knowledge. Edmund Gettier famously presented cases in which we want to say that
someone has justified, true belief but not knowledge. They show that the three conditions
of the tripartite definition are not sufficient for knowledge.
Gettier, ‘is justified true belief knowledge?’
Gettier starts by claiming, uncontroversially, that deductive argument preserves
justification. Suppose you are justified in believing that p (say, that Socrates is a man and
that all men are mortal), and p entails another proposition, q (that Socrates is mortal). If you
deduce that q from p, you are also justified in believing that q.
He then gives two counterexamples to the tripartite definition. We’ll just look at the first
one. Smith and Jones are applying for the same job. Smith has excellent reason to believe
that Jones will get the job, e.g. Smith has been told this by the employer. Smith also has
excellent reason to believe that Jones has ten coins in his pocket, e.g. Smith has just
counted them. Therefore, both of these beliefs are justified. Smith then puts the two beliefs
together and deduces that the man who will get the job has ten coins in his pocket. This
belief is justified, because it is inferred deductively from justified beliefs. It turns out that
Jones doesn’t get the job, Smith does. It also so happens that, unknown to him, Smith also
has ten coins in his pocket. So Smith’s belief that the man who will get the job has ten coins
in his pocket is true.
Smith’s belief is both true and justified, but we shouldn’t say that Smith knows that the man
who will get the job has ten coins in his pocket. Smith inferred his belief from a false belief,
namely that Jones would get the job. So the reason Smith has for his belief is false. What
makes his belief true (Smith, who has ten coins in his pocked, gets the job) has come apart
from what justifies his belief (his justified belief that Jones, who has ten coins in his pocket,
will get the job). There is no connection between what justifies his belief and his belief’s
being true.
Other examples of justified true belief without knowledge became known as ‘Gettier cases’.
They all describe situations in which we have justified true belief, but not knowledge, by
demonstrating how the belief is only accidentally true, given the evidence that justifies it. So
justified true belief is not sufficient for knowledge. That means it is not the same as
knowledge. If knowledge isn’t justified true belief in these cases, then knowledge is never
justified true belief.
How might the defender of the tripartite theory of knowledge reply?
Add a ‘no false lemmas’ condition (J+T+B+N)
Smith doesn’t know that the man who will get the job has ten coins in his pocket, we said,
because he inferred this belief from a false belief, namely that Jones will get the job. So all
we need to do is rule this out in the definition of knowledge by adding an extra condition. You
know that p if
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p is true
you believe that p
your belief that p is justified
you did not infer that p from anything false.
Condition (4) is called the ‘no false lemmas’ condition. A lemma is a claim part way through
an argument. Smith concluded that Jones will get the job from being told by the employer;
and he then used that information to conclude that the man with ten coins in his pocket will
get the job. So ‘Jones will get the job’ is a lemma.
This addition certainly deals with Gettier’s examples. But it doesn’t deal with the underlying
worry about truth and justification ‘coming apart’. There are Gettier cases in which you don’t
make an inference, so condition (4) is satisfied, but you still don’t have knowledge. Here’s a
famous example from Alvin Goldman, ‘Discrimination and Perceptual Knowledge’: Henry is
driving through the countryside. He doesn’t know it, but in this part of the country – call it
‘Barn County’ – there are lots of fake barns, just barn facades. But they have been built so
that they look just like real barns when seen from the road. As he drives along, Henry often
thinks ‘There’s a barn’, or ‘Hey, there’s another barn.’ These beliefs don’t count as
knowledge because they are false. But just once, Henry thinks ‘There’s a barn’ when he is
looking at the one and only real barn in the area. This belief is true. And it is justified – it is
formed from normal perception and Henry, of course, has no reason to suspect that he is the
victim of an elaborate hoax. If our normal perceptual beliefs are justified, then so is Henry’s
belief. But it is not knowledge, because – as in Gettier cases – it is only a matter of luck that
Henry’s belief is true in this one instance.
Henry hasn’t inferred that there’s a barn from something false. First, forming beliefs from
perception isn’t a matter of inference – we simply believe what we see. Second, suppose it
were a matter of inference. Suppose Henry thinks ‘It appears to me as though there is a barn.
Appearance is a good guide to reality. Therefore, there is a barn.’ None of these claims is
false, so he has not inferred ‘There is a barn’ from any false lemmas. (If Henry relies on the
belief ‘Appearance is a good guide to reality around here’, then this would be a false lemma.
But who thinks like this?!)
Infallibilism
The tripartite definition of knowledge does not tell us what it is for a belief to be justified.
Gettier has assumed that Smith’s beliefs – that Jones will get the job and that he has ten coins
in his pocket – are justified. Because they are justified, his deduction that the man who will
get the job has ten coins in his pocket is justified. But we can challenge Gettier’s assumption.
Perhaps Smith’s initial beliefs are not justified or, better, not justified enough to count as
knowledge. If so, then his deduction will not be justified enough either.
Smith has excellent reasons for both his beliefs about Jones getting the job and having ten
coins in his pocket. But infallibilism argues that knowledge is certain. Only certainty can
provide the degree of justification needed to turn true belief into knowledge. We can either
say that a belief is not justified if it is not certain or that it is not sufficiently justified to
count as knowledge if it is not certain. The implication that we should draw from Gettier
cases is that our beliefs are rarely sufficiently justified to count as knowledge.
Descartes, Meditations I Descartes begins Meditation I by declaring that he has known for a
long time that in order to establish anything ‘in the sciences that was stable and likely to last’
(p. 1), he would have to start from the foundations. He does not need to reject as false
everything he thinks he knows, but he needs to avoid believing things ‘that are not completely
certain and indubitable’. To establish this certainty, he seeks to test his beliefs by doubting
them. As he tries to call his beliefs into question, he repeatedly asks how he can know they
are true. So he understands knowledge in terms of what is ‘completely certain and
indubitable’. If we can doubt a belief, then it is not certain, and so it is not knowledge.
So what can we doubt? Descartes doubts the beliefs formed on the basis of what he perceives
and even whether he knows if he is awake or not. He then wonders if he can know what exists
at all. Of course, his ‘habitual opinions’ are highly probable, but they are not certain. To
remind himself of this, he supposes that he is the victim of a massive deception by an evil
demon, telepathically controlling his experiences and thoughts.
Discussion By ‘indubitable’, Descartes doesn’t mean that he has a feeling of certainty. That
could vary from one person to another, e.g. you might feel certain that God exists or that
your friends will never betray you. We can all make mistakes, and be certain of something
when it is not certain. For Descartes, for a belief to be indubitable, it must be infallible in
some way. This is where Descartes’ method of doubt comes in. Using his best, most careful
judgement, what he judges must be true – it is impossible that he could be making a mistake.
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No one can know what is false.
Therefore, if I know that p, then I can’t be mistaken about p.
Therefore, for justification to secure knowledge, justification must guarantee truth.
Therefore, if I am justified in believing that p, I can’t possibly be mistaken.
Therefore, if it is possible that I am mistaken, then I can’t be justified in believing that p.
Therefore, infallibilism is true.
Infallibilism defends the tripartite definition of knowledge and rules out Gettier cases,
because in these cases I do not have justified true belief.
However, it is rare that our evidence rules out the possibility of error. Infallibilism entails
that we have very little knowledge (even if we still have many beliefs that are very
probably true). Descartes brings everything into question. Unless he can build his way back
out using only infallible beliefs, then infallibilism leads to scepticism, rather than secure
knowledge. It would be better to find a definition of knowledge that allowed us more of it.
Rejecting the argument for infallibilism The argument for infallibilism rests on a logical error.
Premise (2), ‘if I know that p, then I can’t be mistaken about p’, has more than one meaning,
depending on how one understands ‘can’t’:
2' It can’t be the case that if I know that p, I am mistaken that p.
We should agree with this, because of (1) ‘No one can know what is false’.
2'' If I know that p, (I am in a position that) I can’t possibly be mistaken that p.
This is what infallibilism assumes in moving from (2) through (3) to (4). It is a much stronger
claim than (2′), because it says that not only am I not mistaken, but I can’t possibly be
mistaken that p. Obviously, there are many cases of perception or memory in which I could be
mistaken that p, but in fact I am not, and my true belief rests on evidence, so there are good
reasons why I am not mistaken.
The argument for infallibilism slips from (2′) (inferred from (1)) to (2″) (to support (4)). But
this is a mistake, confusing one claim for another. (This is called the fallacy of equivocation.)
The two claims are distinct, since one is a claim about whether I am mistaken, and the other
is a claim about whether I could be mistaken. So the argument fails. To accept infallibilism,
we need some other, independent reason to believe (2″).