Substance also is the _final cause_, the _raison d’être_, of the reality of the accidental mode of being. Accidents exist for the perfecting of substances: _accidentia sunt propter substantiam_. As we have seen already, and as will appear more clearly later on, the fundamental reason for the reality of an accidental mode of being, really distinct from the created or finite substance (for the Infinite Substance has no accidents), is that the created substance is imperfect, limited in its actual perfection, does not exist _tota simul_, but develops, through a process of change in time, from its first or _essential_ perfection, through _intermediate_ perfections, till it reaches the _final_ perfection (46) of its being. Have all accidents _efficient causes_? Those which are called common accidents as distinct from _proper_ accidents or _properties_ (66) have undoubtedly efficient causes: the various agencies which produce real but accidental changes in the individual substances of the universe. _Proper_ accidents, however, inasmuch as they of necessity exist simultaneously with the substances to which they belong, and flow from these substances by a necessity of the very essence of these latter, cannot be said to have any efficient causes other than those which contribute by their efficiency to the _substantial changes_ by which these substances are brought into actual existence; nor can they be said to be _caused efficiently_ by these substances themselves, but only to “flow” or “result” necessarily from the latter, inasmuch as they come into existence simultaneously with, but dependently on, these substances. Hence, while substances are universally regarded as _real principles_ of their properties—as, for instance, the soul in regard to intellect and will, or corporeal substance in regard to quantity—they are not really efficient causes of their properties, _i.e._ they do not _produce_ these properties by _action_. For these properties are antecedent to all _action_ of the substance; nor can a created substance _act_ by its _essence_, but only through active powers, or faculties, or forces, which meditate between the essence of a created substance and its actions, and which are the proximate principles of these actions, while the substance or nature is their remote principle. Hence the “properties” which necessarily result from a substance or nature, have as their efficient causes the agencies productive of the substance itself.(253) 66. MAIN DIVISIONS OF ACCIDENTS.—These considerations will help us to understand the significance of a few important divisions of accidents: into proper and common, inseparable and separable. We shall then be in a position to examine the nature of the distinction between accidents and substance, and to establish the existence of accidents really distinct from substance.