Ruth asked:

‘Nothing can be known.’ What is a powerful objection to this claim?

Answer by Helier Robinson

It is self-refuting. If it is true then you cannot know about it. Any self-refuting statement must be false.


Answer by Tony Fahey

The most obvious objection to the old nihilist credo ‘nothing can be known’ is that if it can be shown that the statement ‘nothing can be known’ is valid, then it follows that the statement itself is something that can be known.  Paradoxically, rendering the statement invalid.


Answer by Geoffrey Klempner

Why can’t the sceptic just say, ‘Only one thing can be known, that nothing (else) can be known’?

On the face of it, the qualification, ‘only one thing’ saves the assertion from self-contradiction or being self-refuting. However, the next question would be, ‘What makes this one proposition special?’

Here is one move that the sceptic could make. It is similar to the argument Russell gives about naive realism: ‘Naive realism leads to physics, and physics, if true, shows that naive realism is false. Therefore, naive realism is false.’

So, similarly:

Belief that something can be known leads to epistemology, and epistemology leads to scepticism. So either you’re a sceptic to start with (you don’t believe anything, don’t utter any statement, but just wag your finger) or you are led to scepticism by your assumption that it is possible to know something. Whether you reject the possibility of knowledge without offering any argument, or offer an argument, the conclusion is the same.

Here’s another way of putting the same point, using the logical rule of or-elimination:

1. Either I know something or I know nothing.

2. If I know something, then I know that the proof of scepticism is valid, therefore I know nothing.

3. If I know nothing, then I know nothing.

4. Either way, I know nothing.