The second chapter of the Vaisheshika Sutras presents five substances (earth, air, water, fire, space) each with a distinct quality. Kanada argues that all except "air and space" is verifiable by perception, while existence of invisible air is established by inference (air blows, and that there must be a substance that affects the touch sensation to the skin; space, he argues, is inferred from one's ability to move from one point to another unhindered - a point he revises in later part of the text by asserting that sound is perceived and proves space).