This foundation of all classical reasoning is simply Being. Its study is known as Ontology, as the study of reasoning is logic and the science of obtaining of knowledge is termed epistemology.
A scholastic philosopher takes us through the basics of this profoundly satisfying science which has come alive again in many campuses — firing enthusiasm for the next millennium among those masters and students who are neither afraid of the challenge of unalloyed thought nor appalled by the search for certainty.
NB; Ontology is not to be identified with what has become known as "the ontological proof of God" posited by St Anselm, nor should the Quinque Viae proofs for the existence of God which were developed by Aquinas be mistaken for that pious but less perfected product of reasoning.
Ontology, as has already been made clear, is simply the study of being.
We may consider being as the object primarily apprehended by the intellect either from the stand point of intelligibility — essence.
Or from the standpoint of being in existence which we know as substance,
Or from considering being in action which we term act.
"The essence of a thing is what that thing is necessarily and primarily as the first principle of its intelligibility."
The substance is the thing brought to mind as capable of supporting properties that define it; colour, hardness, heat, etc.
Here we concentrate on the being of things (understanding the term being in its most general and indeterminate sense) from the standpoint of action, in reference to the manner in which things behave in reality, or , if you prefer, in reference to what they do.
What is the first truth which the intellect grasps as soon as it has formed the notion of being?
It is sufficient to consider the notion to see at once that what is, is (principle of identity), or again that what is, cannot not be at the same time and in the same relation (principle of non-contradiction). That is to say, that everything is what it is, that it is not what it is not, and that it is everything that it is.
It is all so self evident. Why do we begin thus? We are cutting to the floor of reasoning, making a solid base for reason. It should be noted that most fallacies arise in modern philosophical systems because they build upon the sand of unintentional relativism.
However will now consider what things do, what is their natural behaviour, what is the primary fact of experience grasped by the senses and the consciousness.
Things change. The arrow flies, the animal runs, what was cold becomes hot under the action of fire, food becomes flesh, what was living dies, and every spring that which had no being evolves into existence. I.e., the seed to the sunflower.
Although like our primary notions, it is very difficult to explain scientifically, everybody knows by experience in what this great fact of change or motion consists. We may say that wherever there is change there is a transition (from one being to another, or from one mode of being to another).
And for transition to exist, there must be something which undergoes it, something which is the subject which ceases to be in a particular place or a particular thing (terminus a quo, the arrow pressed to the bow, the food, the seed). To be in another place or another thing (terminus ad quem, the arrow in the target, the flesh, the mature plan)
Being is prior to change
There is no change without a subject which is changed, and which must be some particular thing before the change is effected - in other words being is prior to change.
Those indeed who maintain that change is prior to being, and there is change without a subject which is changed and which is some particular thing before the change is effected, deny the principle of identity and fall into absurdity.
This is worth cutting in stone. So many fallacious arguments are based upon a denial of identity and the attempted improper separation of necessary subject of change and its transition.
For when they take up this position, they must either continue to accept the notion of being, in which case to affirm that there is change without a subject of change, or that change is prior to being, is to affirm that what has no being, changes, which is manifestly absurd; or they must reject the notion of being as illusory and argue that instead of conceiving being we must conceive change, in which case they must reject as false, together with the notion of being, the principle of identity which is bound up with it, and maintain that thought is essentially deceptive, which is equally absurd.
We are, therefore, absolutely obliged to hold that being is prior to change, and that there is no change without a subject which is changed, and which is some particular thing before it changes; or, in the language of philosophy, that there is no motion without a subject which is moved.
We will now turn away from experience and every sensible representation and attempt to consider change with our intellect, that is to say, in terms of being, the formal object of the latter.
We shall inquire how or in what respect the starting point of the change can thus become a goal. You will answer perhaps, that it is according as it is this or that, in respect of what it is, that the starting point becomes the goal. But the starting point is nothing but what it is, and is already everything that it is, and therefore in this respect is incapable of becoming, for it already is. You may then say that it is according as it is not this or that, in respect of what it is not, that the starting point becomes the goal. But in respect of what it is not, the thing is nothing whatever, in fact it is pure nothing, and therefore cannot be the source of the product of change. It is incapable of becoming, for it simply is not.
Hence the starting point of change cannot become its goal - either in respect of what it is or in respect of what it is not. In other words, the new being which is the product of change can be derived neither from the being which already exists, nor from a nothing, which has no existence whatever.
Is change, therefore, impossible, as Parmenides maintained? And are we obliged with him to deny the evidence of our senses, which witness to the fact of change?
No. But we are obliged to develop and explore our idea of being. Evidently in the analysis we have just made something has been left out. The starting point of change is no doubt already everything which it is, but it is not yet all which it can be; it is not yet that particular thing it is destined to become, but it possesses the means to be it, it can be it. Therefore between being and not being there is the power of being. It is neither in respect of what it is, nor in respect of what it is not, but in respect of what it can be that the starting point of change becomes its goal.
The arrow is here (on the bow, for instance) and from the standpoint of being pure and simple, it is nowhere else; but it can be there (at the goal, for example), and possesses the means to be there. Bread is bread and nothing but bread, and not flesh, so far as it is, in the sense of being pure and simple, that is to say, of being completely realised; but it can cease to be bread and become flesh. There is in it that which enables it to undergo the change under the action of certain determinate causes.
This power in them is as such something real. Consider a man asleep. He neither sees nor speaks nor walks. But he is not therefore blind, paralysed, or dumb. He is really capable of seeing, speaking, and walking. While he does not speak he retains the power to speak, he has it in him; whereas he cannot without a violation of nature become a tree or a bird. Or again take a billiard ball at rest. It is immobile (not moving). But it is not therefore immovable. It is really capable of motion. While it does not move it retains the power of being moved, it has it in itself, whereas it has no natural power of passing through a wall. The power of being is not being in the full and primary sense of the term; but the power of being without as yet being is not sheer non-entity. Power of being taken precisely as such is irreducible either to non-entity or to being pure and simple. It is something different from either, something sui generis for which philosophy must find a place. Precisely so far as things can be something they are not, they, after an inferior fashion, are.
We have thus found something which does not deserve to be called being, on which that title can be bestowed only in a secondary and improper sense, as an alms, so to speak, but which nevertheless is real.
It is what philosophers term potency or potentiality.
In using the term potency, we must be on our guard and against ambiguity. This potency is not that of which we think when we say that a being is potent. This potency is not an active power. Power to effect something to work, at least when understood as active, is the absolute contrary of the power or potency with which we are now concerned, because it is not really potency but act. The potency of which we are speaking is entirely passive, nothing more than a real power of being or becoming. Wax is in potency to receive the impress of the seal, water in potency to become ice or vapour. The active powers (for instance, the faculties of the soul) are also rightly termed potencies or potentialities, but only in so far as they are not, or are capable of not being, actually operative, or so far as they are simple capacities of action or operation.
Here also we must be aware of ambiguity. We are not concerned, at least not primarily and chiefly, with an act, in the ordinary sense of the word, with doing or action. Action or operation is indeed an act, being in act, but it is what is termed the secondary act, (actus operationis). Action presupposes being. And the primary act is the act of being (actus existentiae), moreover of being a particular thing (actus essentiae). For example, a body is luminous in act, even when it is not illuminating anything else. Clay, once modelled is a statue in act, water at 32º Fahrenheit is ice in act, and the moment anything effectively is one thing or another and especially the moment any thing exists, it is in act.
Act may therefore be defined as being in the strict sense of the term, taken in the fullness thus signified, or again the finished, the determinate, or the perfect as such. Potentiality, on the other hand, is the determinable, the perfectible, that which is capable of being finished, as such; not a being but a real power of being.
We must take care not to attempt to think with our imagination these concepts of act and potentiality. They can be thought by the intellect alone. Least of all must we conceive of potentiality as some sort of being in act which we imagine as more or less hazy, indefinite, inactive, and hidden in the object.
Potentiality in itself is absolutely incapable of being represented. It is not a spring or an organ hidden in the thing, nor a character prefigured in it after the fashion of an imaginary statue outlined beforehand by the veins of marble within the block, nor yet an act thwarted or rendered abortive, like an effort or pressure overcome by the resistance of an obstacle. It is absolutely nothing done or in process of doing, absolutely nothing in act. In itself it cannot be conceived (for in that case it would necessarily be conceived as something determinate) It can be conceived only by means of the act, (the particular thing) with which it is correlated, as the simple power of that particular thing.
CONCLUSION
Being, considered in relation to the fullness and perfection which the term signifies, is divided into being in the strict sense or act, and power of being or potentiality.
We are now in a position to understand change. The product of change arises neither out of being in act nor out of nothing, but from potential being. In other words, the action of the efficient cause draws, educes, from the potentiality of the subject the determination, the form, which was wanting in the starting point of the change and characterises its goal, as when the action of fire educes from the potentiality of water, (the water is cold, but can be hot) the determination (a specific intensity of heat) which characterises it as the result of the change. The change is the transition from potentiality to act, or, more accurately, according to a definition to which we must return later, it is the act of a thing in potentiality: taken precisely in respect of its potentiality: actus existentis in potentia prout in potentia