David HUME thought that the generality of Locke's theory of ideas threatened one of its central claims, the claim that there are no innate ideas. At the same time Hume criticizes Malebranche's narrow conception of ideas for failing to account for the role of sensation in the origin of ideas. Hume reconciles the narrow and the wide theories of ideas by dividing perceptions into two classes, impressions and ideas. We have ideas when we think or remember. The distinction between sensation and reflection is maintained by Hume, though unlike Locke, Hume does not distinguish ideas of sensation and reflection, but only impressions of sensation and reflection.
All simple ideas derive from simple impressions.
An impression of desire may result from the idea of pleasure. The idea of pleasure, however, must itself derive from an antecedent impression of pleasure. About the origin of our impressions themselves Hume has little to say. He appears to think that determining the origins of impressions is outside of the bounds of philosophical inquiry. Some commentators take Hume to hold that impressions of sensation are caused by external objects, as Locke held ideas of sense are caused.