This fundamental quadruple distinction of _Entia_, which serves as an introduction to the ten Categories or Predicaments, belongs to words altogether according to their relative places or functions in the proposition; the meanings of the words being classified accordingly. That the learner may understand it, he ought properly to be master of the first part of the treatise De Interpretatione, wherein the constituent elements of a proposition are explained: so intimate is the connection between that treatise and this. The classification applies to _Entia_ (Things or Matters) universally, and is thus a first step in Ontology. He here looks at Ontology in one of its several diverse aspects--as it enters into predication, and furnishes the material for Subjects and Predicates, the constituent members of a proposition. Ontology, or the Science of _Ens quatenus Ens_, occupies an important place in Aristotle's scientific programme; bearing usually the title of First Philosophy, sometimes Theology, though never (in his works) the more modern title of Metaphysica. He describes it as the universal and comprehensive Science, to which all other sciences are related as parts or fractions. Ontology deals with _Ens_ in its widest sense, as an _Unum_ not generic but analogical--distinguishing the derivative varieties into which it may be distributed, and setting out the attributes and accompaniments of _Essentia_ universally; while other sciences, such as Geometry, Astronomy, &c., confine themselves to distinct branches of that whole;[11] each having its own separate class of _Entia_ for special and exclusive study. This is the characteristic distinction of Ontology, as Aristotle conceives it; he does not set it in antithesis to Phenomenology, according to the distinction that has become current among modern metaphysicians. [Footnote 11: Aristot. Metaphys. [Greek: G]. p. 1003, a. 21, 25-33, E. p. 1025, b. 8. [Greek: e)/stin e)pistê/mê tis ê)\ theôrei= to\ o)\n ê(=| o)\n kai\ ta\ tou/tô| u(pa/rchonta kath' au(to/; au(/tê d' e)sti\n ou)demia=| tô=n a)/llôn e)piskopei= _katho/lou peri\ tou= o)/ntos ê(=| o(/n, a)lla\ me/ros au)tou= ti a)potemo/menai peri\ tou/tou theôrou=si to\ sumbebêko/s], &c. Compare p. 1005, a. 2-14.]