Leibniz’s point is that whatever is the subject of perception and consciousness must be truly one, a single “I” properly regarded as one conscious being. An aggregate of matter is not truly one and so cannot be regarded as a single I capable of being the subject of a unified mental life. This interpretation fits nicely with Lebniz’s oft-repeated definition of perception as “the representation in the simple of the compound, or of that which is outside” (Principles of Nature and Grace, sec.2 (1714