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Dreaming and scepticism and knowledge as justified true belief


To: Kokilla B.
From: Geoffrey Klempner
Subject: Dreaming and scepticism and knowledge as justified true belief
Date: 4th May 2011 14:31

Dear Kokilla,

Thank you for your email of 30 April, with your essay for the University of London BA Epistemology module, in response to the question, 'Can you know that you are not dreaming?', and your email of 1 May in response to the question, 'Is there a difference between knowledge and justified true belief?'


This is not a bad essay. In an exam, you would probably get a pass mark although there are some criticisms that I would make.

First, let's look at the question. The question is, 'Can you know that you are not dreaming?' and not, 'What are the consequences for knowledge if you cannot know that you are dreaming?' It is important to make this point.

Descartes argues in the First Meditation that if he does not know that he is not dreaming, then he does not know anything about the external world. For example, if I do not know that I am not dreaming at this moment in time, then I do not know that I am sitting at my desk, writing an email to KB.

However, some philosophers would challenge this claim. They would say that I DO know that I am sitting at my desk, writing an email to KB, even if (or even though) I DO NOT know that I am not dreaming. How is this possible? The philosophers in question REJECT the principle known as 'Closure'.

This principle states that if I know that P, and P entails Q, then I know that Q.

For example, if I know that I am writing an email to KB, and 'I am writing an email to KB' entails 'I am not dreaming' then I must know that I am not dreaming. But from this it follows logically that if I don't know that I am not dreaming then I don't know that I am writing an email to KB!

However, what the examiner wants to know is simply your views on the question whether you can know that you are not dreaming. That's what the question asked. If you come to the conclusion that you cannot know that you are not dreaming, this does not entail scepticism, for the reason given above. You can admit that you don't know that you are not dreaming, while insisting that you do know that you are sitting at a computer reading this email. All you need to do to justify that position is reject the principle of Closure.

OK, so can you know that you are not dreaming? You cite Ryle's argument concerning polar concepts. In order to have a conception of a dream I must also have a conception of an experience which is not a dream. Otherwise, I do not know what the term 'dreaming' means, because I don't understand the distinction that the concept is intended to draw, between valid experience and a dream.

The problem with the argument from polar concepts is that it is not strong enough to defeat the sceptic who says that all my experience may be a dream. Here's an analogy. In order to have a conception of a 'forged banknote' I must understand the difference between forged note and a genuine note. However, it is still possible that, as a result of a hugely successful forgery, all the banknotes in circulation are now forged notes. I know 'what would be' a genuine bank note. But, unfortunately, there aren't any genuine bank notes left! The same applies to dreaming. I know what would be a 'genuine experience', I know what that means, but what I don't know is if any of the experiences that I am having are genuine.

There is an error where you claim that when Descartes says, 'cogito ergo sum' this is intended to have the consequence that 'he must not be dreaming'. In the next paragraph, you give the reason why this is not the case. All Descartes knows at this point is that he exists. Nothing else. He doesn't know that his experience of an external world is genuine until he has successfully defeated the evil demon hypothesis, by proving (or so he thinks) the existence of a God 'who would not deceive me'.

One more point is worth noting: You are right to see the relevance of the Matrix scenario to Descartes' hypothesis of an evil demon. However, the two hypotheses, Matrix and the evil demon, differ in one very important respect. It is a premise of the Matrix hypothesis that a real world exists, in space and time. Even if I am in a pod dreaming of 1999, there is a real world where the pod is located. Whereas in the evil demon scenario, there is no world at all, no physical matter, only me and the evil demon and nothing else.

Knowledge as justified true belief

The crucial point in this question concerns the Gettier counterexamples. You will get credit for trying to make up Gettier counterexamples of your own, rather than relying on examples from the text book. Well done for doing that. Unfortunately, the two examples you give are not sufficiently clear to reassure the examiner that you fully understand the point of the example. So let's go over the first example carefully. I am going to make some changes and adjustments, so that the example 'works' as an effective Gettier counterexample.

John's mum drops him at school. She has a good justification for believing that John is at school, because she saw him go in through the school gates. And John is in fact at school. But John's mum does not know that John is at school. How could this be?

Let's just spell out what is going on here. In order to defeat the theory that knowledge is 'justified true belief' we need an example which satisfies the three conditions of the 'tripartite definition' of knowledge but which, intuitively, we can see is not an example of knowledge. So:

1. P is true: John is at school.

2. S believes that P: John's mother believes that John is at school.

3. S's belief that P is justified: John's mother saw John go through the school gates, so her belief that John is at school is justified.

-- Now, stop and think. How could John's mother not know that John is at school if conditions 1-3 are satisfied?

Here's a possible scenario. John never intended to go to school. He ducked in through the school gates, then waited on the other side for his mother to drive away. Just as he was about to run out of school again, the headmaster caught him and took him to the detention room. If John's plan had succeeded he would not have been at school. Unfortunately, by unfortunate chance, his plan failed. So John's mother's belief that John is at school is only true 'by chance'. That is why it is not knowledge.

I'll leave the second example, of Mary and her baby daughter, as an exercise.

There is a problem, however, with the Gettier argument, which you do seem to pick up on in your essay although this isn't made very clear. Surely, anything that we claim to know does in some sense rely on 'chance' or 'accident' at some point? If we had an infallibilist theory of knowledge according to which 'justification implies truth' there would be no difficulty. Unfortunately, very little if any of our ordinary beliefs satisfy this strict requirement. In the vast majority of cases, we recognize that you can have 'good justification' for a belief but still be wrong. Your belief is false.

But what that means is that, even if your belief is true, that is in some sense a matter of luck or chance. The world is kind to us. It allows us to form lots of true beliefs. But that's just a matter of luck. The world could be less kind -- for example, the world of the Matrix or the world of the evil demon! -- in which case many or most of our beliefs would be false. If you can't disprove the Matrix or evil demon hypothesis, then you are relying on chance. So, once more we are back with the question we started with, 'Can you know you are not dreaming?'

All the best,