When a thing is found always to cause a particular effect, we call that
effect sometimes a =property=, sometimes a =power= of the thing. Thus
the odor of onions is said to be a property of onions, because onions
always cause that particular sensation of smell to arise, when they are
brought near the nose; lead is said to have the property of heaviness,
because it always causes us to have the feeling of weight when we handle
it; a stream is said to have the power to turn a water-wheel, because it
causes the water-wheel to turn; and a venomous snake is said to have the
power to kill a man, because its bite may cause a man to die. Properties
and powers, then, are certain effects caused by the things which are
said to possess them.