(_a_) The attributes which we affirm of substance, other than the notes constitutive of its essence, are divided into _proper_ accidents, or _properties_ in the strict sense (ἴδιον, _proprium_), and _common_ accidents, or accidents in the more ordinary sense (συμβεβηκός, _ac-cidens_). A property is an accident which belongs exclusively to a certain class or kind of substance, and is found _always_ in _all_ members of that class, inasmuch as it has an adequate foundation in the nature of that substance and a necessary connexion therewith. Such, for instance, are the faculties of intellect and will in all spiritual beings; the faculties of speaking, laughing, weeping in man; the temporal and spatial mode of being which characterizes all created substances.(254) When regarded from the logical point of view, as attributes predicable of their substances considered as logical subjects, they are distinguished on the one hand from what constitutes the essence of this subject (as _genus_, _differentia_, _species_), but also on the other hand from those attributes which cannot be seen to have any absolutely necessary connexion with this subject. The latter attributes alone are called _logical accidents_, the test being the absence of a necessary connexion in thought with the logical subject.(255) But the former class, which are distinguished from “logical” accidents and called _logical properties_ (“_propria_”) are none the less _real accidents_ when considered from the ontological standpoint; for they do not constitute the essence of the substance; they are outside the concept of the latter, and super-added—though necessarily—to it. Whether, however, all or any of these “properties,” which philosophers thus classify as real or ontological accidents, “proper” accidents, of certain substances, are _really_ distinct from the concrete, individual substances to which they belong, or are only aspects of the latter, “substantial modes,” only _virtually_ distinct in each case from the individual substance itself,—is another and more difficult question (69). Such a property is certainly not really separable from its substance; we cannot conceive either to exist really without the other; though we can by abstraction think, and reason, and speak, about either apart from the other.(256) Real inseparability is, however, regarded by scholastic philosophers as quite compatible with what they understand by a real distinction (38). A _common_ accident is one which has no such absolutely necessary connexion with its substance as a “property” has; one which, therefore, can be conceived as absent from the substance without thereby entailing the destruction of the latter’s essence, or of anything bound up by a necessity of thought with this essence. And such common accidents are of two kinds.