Metaphysics is traditionally divided into Ontology, or the philosophy of being, Cosmology, or the philosophy of nature, and Psychology, or the philosophy of mind.
Ontology, dealing with the most general characteristics of the real, includes those subjects which, as common to the other two branches, cannot be dealt with by either exclusively.
Cosmology and Psychology study, in a very general way, one or other of the concrete forms which reality takes, while Ontology is concerned only with the nature of the real in abstraction from its specific embodiments.
Hastings, J (Ed.) (1917) Encyclopaedia of Religion and Ethics IX, Edinburgh: T & T Clark.