Any answer to the question, Why is liberty so valuable? presupposes that there are real values and that we can know them. Yet more than one argument for liberty has tacitly or explicitly rested upon scepticism about the reality and knowability of values. It is a familiar claim that, since there is nothing good or bad in itself, or because we cannot know that anything is really good or bad, we should be free to hold and express our own beliefs and to adopt our own ways of life. But such an argument manifests that suspended logic of which Polanyi complained. For it fails to recognise that, if indeed nothing is or can be known to be really good or bad, then there is nothing good or known to be good about liberty and nothing bad or known to be bad about tyranny and slavery. The liberalism of scepticism undercuts itself.