All that can fall within the compass of human understanding, being either, the nature of things, as they are in themselves, their relations, and their manner of operation: or, that which man himself ought to do, as a rational and voluntary agent, for the attainment of any end, especially happiness: or, the ways and means whereby the knowledge of both the one and the other of these is attained and communicated; I think science may be divided properly into these three sorts:.