Hume's Model of Mind

Hume's model of mind is founded on Lockean empiricism, and aims to offer a better alternative to the rationalist idea that the mind alone can tell us anything about the world. It retains the notion that by sense impressions, simple and complex ideas are formed. Hume's modification incorporates a clarification on Locke's ambiguous use of 'idea', to now refer separately to perceptions of sensations (such as the idea of a tree) and those of reflection (the concept of the tree). Space and time, which were classed as simple ideas for Locke became complex ideas for Hume. Locke's reification of ideas is controversial (he refers to the "immediate objects" of understanding). Hume however reifies all perceptions as substances, to the point that they could exist independent of the perceiver. Perceivers are merely "bundles" of perceptions; Hume illustrates this by stating that upon introspection, it is not possible to include the self in his field of observation.

Ideas are 'copies' of impressions, caused by them, although the distinction is arguably one of vivacity or intensity. The faculties of memory and imagination allow us to process them; the former "corresponds to the strict order of reality" and the latter combines the ingredients given in experience. Simple ideas are direct copies of simple impressions, e.g. blue. A complex idea need not have a corresponding complex impression, but is necessarily founded on simpler ideas from simple impressions, e.g. a blue elephant. This example has often been used to counter the notion of simple and complex ideas, since "blue" is arguably a complex idea, only making any sense when referenced to all other colours and absence of colours.