 The basis of this accusation was Leibniz’s attribution to the soul of only two basic faculties: perception, the representation of multiplicity in a simple soul, and appetition, which he defines as “the action of an internal principle which brings about change or the passage from one perception to another” (G 6: 608–9). Perceptions, in Leibniz, as in Descartes, are thoughts — presentations in the mind. The perceptual thought that there is a green tree in front of me is not absolutely unlike the mathematical thought that triangles have three angles. Perception of material objects is “confused” because — according to the Cartesian tradition — corporeal substance has no colours or other sensory properties — which come into being through the interaction of the mind and tiny, single imperceptible, uncoloured corpuscles of matter. Though Leibniz denied the existence of purely material corpuscles and the possibility of causal influx or even interaction between real substances, he agreed that, from the perspective of what he sometimes terms mere physical science, perception required interaction, and that corpuscular motions were involved in the perception of sensory qualities such as light and colour. Perception can therefore be said to confuse what reason delivers to us clearly (A 132, 219, 403). Though we are unable to grasp the sufficient reason of particular colours, there is nothing arbitrary in their connection with their underlying causes (A 382f).