The punchline to the following famous philosophical anecdote:

The philosopher and churchman George Berkeley, if I understand him correctly, put forward the contention that nothing is real, in the sense that the universe exists only in our perceptions.

It was commented at the time that this theory, while radical, could not be refuted, any more than it could be proved. Samuel Johnson, however, took a different view. When asked by Boswell what he thought of Berkeley's theory that matter may not, in fact, exist, Johnson kicked hard at a stone and stated, "I refute him thus!"