Bertrand Russell

“Consider 'the present King of France is bald.' Here 'the present King of France' has a primary occurrence, and the proposition is false.”

“For if we cannot be sure of the independent existence of objects, we cannot be sure of the independent existence of other people's bodies, and therefore still less of other people's minds, since we have no grounds for believing in their minds except such as are derived from observing their bodies.”

“Form now the assemblage of all classes which are not members of themselves. This is a class: is it a member of itself or not?”