In the fifth chapter of Vaisheshika Sutra, Kaṇāda mentions various empirical observations and natural phenomena such as the falling of objects to the ground, rising of fire and heat upwards, the growth of grass upwards, the nature of rainfall and thunderstorms, the flow of liquids, the movement towards a magnet among many others, asks why these things happen, then attempts to integrate his observations with his theories on atoms, molecules, and their interaction. He classifies observed events into two: those caused by volition, and those caused by subject-object conjunctions.