Those, then, are the principal kinds of change, as analysed by Aristotle and the scholastics. We may note, finally, that the distinction between immanent and transitive activity is also applied to change—that is, to change considered as a process, not to the result of the change, to change in fieri, not in facto esse. Immanent movement or activity (motio, actio immanens) is that of which the term, the educed actuality, remains within the agent—which latter is therefore at once both agens and patiens. Vital action is of this kind. Transitive movement or activity, on the other hand (motio, actio transiens), is that of which the term is some actuality educed in a being other than the agent. The patiens is here really distinct from the agens; and it is in the former, not in the latter, that the change takes place: actio fit in passo. All change in the inorganic universe is of this sort ([101]).
Chapter III. Existence And Essence.
12. Existence.—In the preceding chapters we examined reality in itself and in its relation to change or becoming. We have now to examine it in relation to its actual existence and to its intrinsic possibility (7, a).
Existing or being (in the participial sense: esse, existere, τὸ εἶναι) is a simple, indefinable notion. A being is said to exist when it is not merely possible but actual, when it is not merely potential in its active and passive causes but has become actual through those causes (existere: ex-sisto: ex-stare: to stand forth, distinct from its causes); or, if it have no causes, when it simply is (esse),—in which sense God, the Necessary, purely Actual Being, simply is. Thus, existence implies the notion of actuality, and is conceived as that by which any thing or essence is, distinct from nothingness, in the actual order.[83] Or, again, it is the actuality of any thing or essence. About any conceivable being we may ask two distinct questions: (a) What is it? and (b) Does such a being actually exist? The answer to the former gives us the essence, what is presented to the mind through the concept; the answer to the latter informs us about the actual existence of the being or essence in question.
To the mind of any individual man the real existence (as also the real essence) of any being whatsoever, not excepting his own, can be known only through its ideal presence in his mind, through the concept or percept whereby it becomes for him a “known object,” an objectum cognitum. But this actual presence of known being to the knowing mind must not be confounded with the real existence of such being (4). Real being does not get its real existence in our minds or from our minds. Our cognition does not produce, but only discovers, actually existing reality. The latter, by acting on the mind, engenders therein the cognition [pg 075] of itself. Now all our knowledge comes through the senses; and sense cognition is excited in us by the direct action of material or phenomenal being on our sense faculties. But through sense cognition the mind is able to attain to a knowledge both of the possibility and of the actual existence of suprasensible or spiritual realities. Hence we cannot describe existence as the power which material realities have to excite in us a knowledge of themselves. Their existence is prior to this activity: prius est esse quam agere. Nor can we limit existence to material realities; for if there are spiritual realities these too have existence, though this existence can be discerned only by intellect, and not by sense.
13. Essence.—In any existing thing we can distinguish what the thing is, its essence, from its actual existence. If we abstract from the actual existence of a thing, not considering whether it actually exists or not, and fix our attention merely on what the thing is, we are thinking of its real essence. If we positively exclude the notion of actual existence from our concept of the essence, and think of the latter as not actually existing, we are considering it formally as a possible essence. There is no being, even the Necessary Being, whose essence we cannot think of in the former way, i.e. without including in our concept the notion of actual existence; but we cannot without error positively exclude the notion of actual existence from our concept of the Necessary Being, or think of the latter as a merely possible essence.
Taken in its widest sense, the essence of a thing (οὐσία, essentia, τὸ τί ἐστι, quod quid est, quidditas) means that by which a thing is what it is: id quo res est id quod est: that which gives us the answer to the question, What is this thing? Quid est haec res? τί ἐστι τόδε τι.[84] Now of course any individual thing is what it is just precisely by all the reality that is in it; but we have no direct or intuitive intellectual insight into this reality; we understand it only by degrees; we explore it from various [pg 076] points of view, abstracting and generalizing partial aspects of it as we compare it with other things and seek to classify and define it: ratio humana essentias rerum quasi venatur, as the scholastics say: the human mind hunts, as it were, after the essences or natures of things. Understanding the individual datum of sense experience (what Aristotle called τόδε τι, or οὐσία πρώτη, and the scholastics hoc aliquid, or substantia prima), e.g. this individual, Socrates, first under the vaguest concept of being, then gradually under the more and more determinate concepts of substance, corporeal, living, sentient, rational, it finally forms the complex concept of his species infima, expressed by his lowest class-name, “man,” and explicitly set forth in the definition of his specific nature as a “rational animal”. Nor does our reason fail to realize that by reaching this concept of the specific essence or nature of the individual, Socrates, it has not yet grasped all the reality whereby the individual is what he is. It has reached what he has in common with all other individuals of his class, what is essential to him as a man; it has distinguished this from the unanalysed something which makes him this particular individual of his class, and which makes his specific essence this individual essence (essentia “atoma,” or “individua”); and it has also distinguished his essence from those accidental and ever varying attributes which are not essential to him as a man, and from those which are not essential to him as Socrates. It is only the unfathomed individual essence, as existing hic et nunc, that is concrete. All the mind's generic and specific representations of it—e.g. of Socrates as a corporeal substance, a living being, a sentient being, a rational animal—are abstract, and all more or less inadequate, none of them exhausting its knowable reality. But it is only in so far as the mind is able to represent concrete individual things by such abstract concepts, that it can attain to intellectual knowledge of their nature or reality. Hence it is that by the term “essence,” simply and sine addito, we always mean the essence as grasped by abstract generic or specific concepts (ἔιδος, species), and as thus capable of definition (λόγος, ratio rei). “The essence,” says St. Thomas, “is that by which the thing is constituted in its proper genus or species, and which we signify by the definition which states what the thing is”.[85] Thus understood, the essence is abstract, and [pg 077] gives the specific or generic type to which the individual thing belongs; but we may also mean by essence, the concrete essence, the individual person or thing (persona, suppositum, res individua). The relations between the objects of those two concepts of essence will be examined later.
Since the specific essence is conceived as the most fundamental reality in the thing, and as the seat and source of all the properties and activities of the thing, it is sometimes defined or described, in accordance with this notion of it, as the primary constitutive of the thing and the source of all the properties of the thing. Conceived as the foundation of all the properties of the thing it is sometimes called substance (οὐσία, substantia). Regarded as the source of the thing's activities, and the principle of its growth or development, it is called the nature of the thing (φύσις, natura, from φύω, nascor).[86]