Aristotle's system may be called theistic and dualistic; Plotinus's is pantheistic and monistic. In Aristotle matter is not created by or derived from God, who is external to the universe. Plotinus derives everything from God, who through his powers or activities pervades all. The different gradations of being are static in Aristotle, dynamic in Plotinus. Plotinus assumes an absolute cause, which he calls the One and the Good. This is the highest and is at the top of the scale of existence. It is superior to Being as well as to Thought, for the latter imply a duality whereas unity is prior to and above all plurality. Hence we can know nothing as to the nature of the Highest. We can know only _that_ He is, not _what_ he is. From this highest Being proceeds by a physical necessity, as light from a luminous body or water from an overflowing spring, a second _hypostasis_ or substance, the _nous_ or Reason. This is a duality, constituting Being and Knowledge. Thus Thought and Being hold a second place in the universe. In a similar way from Reason proceeds the third hypostasis or the _World-Soul_. This stands midway between the intelligible world, of which it is the last, and the phenomenal world, of which it is the first. The Soul has a dual aspect, the one spiritual and pertaining to the intelligible world, the other, called _Nature_, residing in the lower world. This is the material world of change and decay. Matter is responsible for all change and evil, and yet matter, too, is a product of the powers above it, and is ultimately a derivative of the Absolute Cause, though indirectly. Matter is two-fold, intelligible and sensible. The matter of the lower world is the non-existent and the cause of evil. Matter in a more general sense is the indeterminate, the indefinite and the potential. Matter of this nature is found also in the intelligible world. The Reason as the second hypostasis, being an activity, passes from potentiality to actuality, its indeterminateness being made determinate by the One or the Good. This potentiality and indeterminateness is matter, but it is not to be confused with the other matter of the phenomenal world. Man partakes of the intelligible, as well as of the sensible world. His body is material, and in so far forth partakes of the evil of matter. But his soul is derived from the universal soul, and if it conducts itself properly in this world, whither it came from without, and holds itself aloof from bodily contamination, it will return to the intelligible world where is its home.