 Hume held a version of the sense-datum theory, which treated such data as mental or phenomenal items. Indeed, he provided what became the first standard argument for the existence of sense data, the Argument from Perceptual Variation, which holds that, for things that we believe to possess stable properties such as shape, size, or color, our experiences of those things vary with the perceiver’s physiological state and spatial position; hence, we cannot equate the shape we perceive with the thing’s actual shape. In fact, Descartes (Meditations [1985: 56–61]), Locke (Essay, bk 2, chs. 8–9), and Berkeley (Principles, pt 1, art. 14) all produced arguments that noted the variation of sensory ideas in relation to actual or purported properties of material objects, using these arguments to distinguish immediately perceived sensory ideas and their intentional contents from the latter objects. But it is Hume who clearly used the Argument to support the Classical Notion of sense data.