Things are relative as double to half and treble to a third, and in general that which contains something else many times to that which is contained many times in something else, and that which exceeds to that which is exceeded; as that which can heat to that which can be heated, and that which can cut to that which can be cut, and in general the active to the passive; as the measurable to the measure and the knowable to knowledge and the perceptible to perception.