Following John Locke’s empiricism and refutation of innate ideas, David Hume (1711 – 1776) argues that knowledge of the world comes from experience. To be more technical, humans have simple sense impressions (e.g., a speck of color), and afterward they have simple ideas of the impressions. Humans then combine these simple ideas into complex ideas (e.g., a tree).

More significantly, for Hume, complex ideas should be able to be traced backwards in this operation because only ideas that come from impression can be considered true. Is the complex idea of a tree traceable back to simple impressions? Each part of the idea of the tree (shape, color, the sound in the wind, etc.) can be traced back to simple ideas that were used to construct it. Also, each simple idea can be traced back to a simple sense impression.

The idea of the self is a complex one: a lived unity that proceeds (and changes) through time. Can the idea of the self be traceable back to simple impressions? The complex idea can be broken down into simple ideas (e.g., particular feelings, perceptions, judgments, and actions), and these simple ideas can be broken down into simple impressions just like the idea of the tree was broken down.

Unlike the tree, the connection of one part to another cannot be observed. The feelings, perceptions, etc., that humans have are connected only succession. What ties the succession of perceptions together? Answering with the self commits the fallacy of begging the question. The self as the unifier is presupposed and not proven. It appears to be the case that the self as a complex idea is combined from simple ideas and then laid back over the flow of experience to be the subject of perceptions, etc. For Hume, there is no philosophical justification for this combination of simple ideas into the idea of the self.

If the self is, instead, thought to be a single unit (that is, a simple idea), then it must be traceable to a simple impression. Moreover, this impression must be invariably throughout one’s life. A human must have the same impression at 7 and at 77. However, there are no impressions that humans have that are invariably the same.