Every thing is conducted by springs and principles …
Hume, Treatise, p. 397.
At the close of the section on personal identity in the Treatise, Hume distinguishes the intellectual world and the natural world (p. 263). The Appendix to this work speaks of the intellectual and material worlds (p. 633;cf.p. 232). His essay, “Of Some Remarkable Customs, ” refers to the moral and physical worlds.1 The intellectual or moral world is the domain of impressions, ideas, perceptions, passions, judgment, the imagination, reason and understanding. That world also includes the perceiver, the self and the mind. It is a world which contains the principles of association, of belief formation, idea acquisition. That same intellectual and moral world contains the various items in Books ii and iii of the Treatise: emotions, moral principles, the self as moral agent.
The natural or material world is the concern of anatomy and natural philosophy (Treatise, p. 276). It is the world of external objects, of principles such as elasticity, gravity, or communication of motion by impulse. That world is the domain of physiology, of nerves and brain. It also seems to contain mechanisms that account for and cause the powers and operations of bodies. The phrase he uses to refer to this mechanism, “springs and principles, ” may suggest a mechanical concept of nature, or it just may be an analogy borrowed from machines such as clocks which were run by pulleys and springs.2 Much of both the natural and intellectual worlds is available to experience and observation, that is the way we discover explanatory principles, if not actual operating princi____________________