We may call attention here to a few other questions of minor import discussed by scholastics. First, have all individuals of the same species the same _substantial_ perfection, or can individuals have different grades of substantial perfection within the same species? All admit the obvious fact that individual differs from individual within the same species in the number, variety, extent and intensity of their accidental properties and qualities. But, having the human soul mainly in view, they disagree as to whether the substantial perfection of the specific nature can be actualized in different grades in different individuals. According to the more common opinion there cannot be different _substantial_ grades of the same specific nature, for the simple reason that every such grade of substantial perfection should be regarded as specific, as changing the species: hence, _e.g._ all human souls are substantially equal in perfection. This view is obviously based upon the conception of specific types or essences as being, after the analogy of numbers, immutable when considered in the abstract. And it seems to be confirmed by the consideration that the intrinsic principle of individuation is nothing, or adds nothing, _really distinct_ from the specific essence itself. Another question in connexion with individuation has derived at least an historical interest from the notable controversy to which it gave rise in the seventeenth century between Clarke and Leibniz. The latter, in accordance with the principles of his system of philosophy,—the _Law of Sufficient Reason_ and the _Law of Continuity_ among the _monads_ or ultimate principles of being,—contended that two individual beings so absolutely alike as to be _indiscernible_ would be _eo ipso identical_, in other words, that the reality of two such beings is impossible.