Paul Broks looks at the philosopher Ludwig Wittgenstein and the problem of "other minds". How do I know you are not a zombie who behaves like a human but actually has no consciousness? Even if you are conscious, how can I tell that what I experience as red, you do not experience as blue? I know...

If a tree falls in a forest and nobody is there to hear it, does it make a sound? That's the kind of head-scratching question that's popularly believed to occupy the time and brains of philosophers. It relates to the ideas of immaterialism proposed by Bishop George Berkeley who asserted that the...