Further, every system of metaphysical philosophy is bound to deal with more special problems, which readily fall into two principal classes. It has to consider the meaning and validity of the most universal conceptions of which we seek to understand the nature of the individual objects which make up the experienced physical world, “extension,” “succession,” “space,” “time,” “number,” “magnitude,” “motion,” “change,” “quality,” and the more complex categories of “matter,” “force,” “causality,” “interaction,” “thinghood,” and so forth. Again, Metaphysics has to deal with the meaning and validity of the universal predicates by which we seek to interpret the nature of the experiencing mind itself, and its relation both to other minds and to the objects of the physical world, “the soul,” “the self,” “the subject,” “self-consciousness,” “ethical purpose,” and so forth. Hence it has been customary to recognise a second and third part of Metaphysics, dealing respectively with the most general characteristics of external Nature and of conscious Mind. These sections of the subject are commonly known as _Cosmology_ and _Rational Psychology_. In Hegel’s system they appear in a double form: in their most abstract generality they constitute the “Doctrine of Essence,” and the “Doctrine of the Notion” in the Hegelian _Logic_; in their more concrete detail they form the second and third parts of his complete system or “Encyclopædia” of the philosophical sciences, the previously mentioned Philosophies of _Nature_ and _Mind_. In the pre-Kantian eighteenth century it was not unusual to add yet a fourth division to Metaphysics, _Rational Theology_, the doctrine of the existence and attributes of God, so far as they can be deduced from general philosophical principles apart from the appeal to specific revelation. Kant’s onslaught on the whole Wolffian scheme in the “Dialectic of Pure Reason,” while profoundly modifying for the future the view taken by metaphysicians of Cosmology and Rational Psychology, proved annihilating so far as eighteenth-century Deism and its philosophical offspring, Rational Theology, were concerned, and that sub-division may fairly be said to have disappeared from subsequent philosophical systems.[29]