In order, therefore, that a thing which is not now actual, but only intrinsically or absolutely possible, become actual, there must actually exist some being or beings endowed with the active power or potency of making this possible thing actual. The latter is then said to be relatively, extrinsically possible—in relation to such being or beings. And obviously a thing may be possible relatively to the power of one being, and not possible relatively to lesser power of another being: the statue that is intrinsically possible in the block of marble, may be extrinsically possible relatively to the skilled sculptor, but not relatively to the unskilled person who is not a sculptor.
Furthermore, relatively to the same agent or agents, the production of a given effect, the doing of a given thing, is said to be physically possible if it can be brought about by such agents acting according to the ordinary course of nature; if, in other words they have the physical power to do it. Otherwise it is said to be physically impossible, even though metaphysically or intrinsically possible, e.g. it is physically impossible for a dead person to come to life again. A thing is said to be morally possible, in reference to free and responsible agents, if they can do it without unreasonable inconvenience; otherwise it is considered as morally impossible, even though it be both physically and metaphysically possible: as often happens in regard to the fulfilment of one's obligations.
That which is both intrinsically and extrinsically possible is said to be adequately possible. Whatever is intrinsically possible is also extrinsically possible in relation to God, who is Almighty, Omnipotent.
8. (b) Subjective “Potentia,” Active and Passive.—Furthermore, we conceive the Infinite Being, Almighty God, as capable of creating, or producing actual being from nothingness, i.e. without any actually pre-existing material out of whose passive potentiality the actual being would be developed. Creative power or activity does not need any pre-existing subject on which to exercise its influence, any subject in whose passive potentiality the thing to be created is antecedently implicit.
But all other power, all activity of created causes, does require some such actually existing subject. If we examine the activities of the agencies that fall within our direct experience, whether in external nature or in our own selves, we shall find that in no case does their operative influence or causality extend beyond the production of changes in existing being, or attain to the production of new actual being out of nothingness. The forces of nature cannot produce an oak without an acorn, or an iceberg without water; nor can the sculptor produce a statue except from some pre-existing material.
The natural passive potentiality of things is, moreover, limited in reference to the active powers of the created universe. These, for example, can educe life from the passive potentiality of inorganic matter, but only by assimilating this matter into a living organism: they cannot restore life to a human corpse; yet the latter has in it the capacity to be restored to life by the direct influence of the Author of Nature. This special and supernatural potentiality in created things, under the influence of Omnipotence, is known as potentia obedientalis.[72]
This consideration will help us to realize that all reality which is produced by change, and subject to change, is essentially a mixture of becoming and being, of potential and actual. The reality of such being is not tota simul. Only immutable being, whose duration is eternal, has its reality tota simul: it alone is purely actual, the “Actus Purus”; and its duration is one eternal “now,” without beginning, end, or succession. But mutable being, whose duration in actual existence is measured by time, is actualized only successively: its actuality at any particular instant does not embody the whole of its reality: this [pg 055] latter includes also a “was” and “will be”; the thing was potentially what it now is actually, and it will become actually something which it now is only potentially; nor shall we have understood even moderately the nature or essence of any mutable being—an oak-tree, for example—until we have grasped the fact that the whole reality of its nature embraces more than what we find of it actually existing at any given instant of its existence. In other words, we have to bear in mind that the reality of such a being is not pure actuality but a mixture of potential and actual: that it is an actus non-purus, or an actus mixtus.
We have to note well that the potential being of a thing is something real—that it is not merely a modus loquendi, or a modus intelligendi. The oak is in the acorn in some true and real sense: the potentiality of the oak is something real in the acorn: if it were not so, if it were nothing real in the acorn, we could say with equal truth that a man or a horse or a house is potentially in the acorn; or, again with equal truth, that the oak is potentially in a mustard-seed, or a grain of corn, or a pebble, or a drop of water. Therefore the oak is really in the acorn—not actually but potentially, potentia passiva.
The oak-tree is also really in those active forces of nature whose influence on the acorn develop the latter into an actual oak-tree: it is in those causes not actually, of course, but virtually, for they possess in themselves the operative power—potentia activa sive operativa—to educe the oak-tree out of the acorn. These two potential conditions of a being—in the active causes which produce it, and in the pre-existing actual thing or things from which it is produced—are called each a real or subjective potency, potentia realis, or potentia subjectiva, in distinction from the mere logical or objective possibility of such a being.
And just as the passive potentiality of the statue is something real in the block of marble, though distinct from the actuality of the statue and from the process by which this is actualized, so is the active power of making the statue something real in the sculptor, though distinct from the operation by which he makes the statue. If an agent's power to act, to produce change, were not a reality in the agent, a reality distinct from the action of the latter; or if a being's capacity to undergo change, and thereby to become something other, were not a reality distinct from the process of change, and from the actual result of this process—it would follow not only that the actual alone is real, and [pg 056] the merely possible or potential unreal, but also that no change can be real, that nothing can really become, and nothing really disappear.[73]