Sophie's World

by Jostein Gaarder

‘When Hume discusses the force of habit, he concentrates on “the law of causation.” This law establishes that everything that happens must have a cause. Hume used two billiard balls for his example. If you roll a black billiard ball against a white one that is at rest, what will the white one do?’ ‘If the black ball hits the white one, the white one will start to move.’ ‘I see, and why will it do that?’ ‘Because it was hit by the black one.’ ‘So we usually say that the impact of the black ball is the cause of the white ball’s starting to move. But remember now, we can only talk of what we have actually experienced.’ ‘I have actually experienced it lots of times. Joanna has a pool table in her basement.’ ‘Hume would say the only thing you have experienced is that the white ball begins to roll across the table. You have not experienced the actual cause of it beginning to roll. You have experienced that one event comes after the other, but you have not experienced that the other event happens because of the first one.’