A professor was explaining the Metaphysics of Morals : "In order for something to be an object of our practical existence, it must be capable of moving us to try to bring it into existence. For example, if I desire shelter from rain, the concept of a lean-to is capable of moving me to cut branches, tie them together, and set them at an angle to the ground."
Someone from the back of the class added : "Or you could buy an umbrella."
