 As we saw in the first section, with respect to oneness, Leibniz famously claims that only something with true unity is truly real. For Leibniz, what truly is is substance, so it is not surprising that at one point he clarifies his definition of perception by saying that perception is “the expression of many things in one, or in simple substance” (A New Method of Learning and Teaching Jurisprudence, revision notes of 1697–1700; A VI, i, 272/L 91).