 On the basis of these empirical cognitions of the soul, rational psychology seeks to draw inferences regarding the soul’s essence and nature. Wolff argues that the soul must be immaterial given that it is impossible that a body should think (GM §738), and as a result that the soul is a simple substance endowed with a power of which its thoughts are effects, which power is identified as a power of representation (GM §§742–7). This secures the soul’s natural immortality, or incorruptibility, but Wolff argues for the soul’s personal immortality, or its preservation of its state of conscious representation and memory in the afterlife (GM §§925–6). It is in the context of rational psychology that Wolff also offers a defence of the Leibnizian doctrine of pre-established harmony (§765), which he think accounts for the empirically-observed agreement between the states of the soul and the body better than the competing systems of physical influence and occasional causation.