As Bergson justly remarked, every self-consistent philosophy starts from an intuition which governs its entire development. What Bergson was saying, in effect, is that the object of metaphysical inquiry must be sought in something first and unconditioned, hence not derived from or reduced to anything else, while everything reduces to it. It need hardly be mentioned that unless this fundamental of a philosophical system is properly identified and properly defined, there can be no firm grasp of the system. In the case of St. Thomas there is no doubt what constitutes the root of his system; it is, unmistakably, being, from the apprehension of which, as from its generative source, issues every ramification of his metaphysical thought. St. Thomas, on this point, expresses himself as follows: "What the intellect first conceives, on the ground that it is the most known object, is being; and to being it reduces all its conceptions." Or, in his Latin,
Thud autem quod primo intellectus concipit quasi notissimum et in quo omnes conceptiones resolvit est ens. 1
Thereby he expresses both the universality and the primacy of being, and of the corresponding notion of being. Every conception of the mind can, as we have just heard, be reduced to the notion of being; which implies that objectively, as well as conceptually, everything is being. This recognition that everything is being is absolutely primary; for it is a recognition of the object which, in itself,2 is most known, that is, first and last and wherever anything is known.
Still, it is one thing to say that being is the first and most universal notion, and quite another to catch the full significance. There is, to be sure, a common acquaintance with being, and with the notion of being; but this is to know the thing but dimly, the seeds of knowledge, not the harvest. The mature grasp of the factors of being and its notion calls for minds disciplined to think and rethink philosophically. Nor even then will it all come at once, nor, de facto, in one generation. It is quite consistent that through the centuries the human mind has given, and still gives, much time and effort to the pursuit of being, to see what lies in this, its first and most universal recognition. Parmenides, to speak for a moment historically, has already been mentioned as the first to see clearly that being is primary both on the side of reality and on the side of thought. But Parmenides bore the tradition of the Physicists, the earliest Greek philosophers of corporeal nature, who saw scarcely beyond the realm of matter. The tradition left its mark; for though the Parmenidean being is immobile (changeless) and undivided, it is still nothing more than the sum total of the world perceived by the senses. Thus the ontology (science of being) of Parmenides could not but fail to rise above the corporeal level. Where he failed, Plato in large measure succeeded, not only, by the world of Ideas, surmounting the being of sense, but also restoring to being its multiplicity and becoming. Thereafter, by progressive discovery, Aristotle and still later St. Thomas will both of them strike the true notion of being - a notion transcendent and analogical.
The notion of being can be traced psychologically as well as historically; in other words, the unique circumstances in which the notion of being finds itself appear, perhaps most readily, when we stop to analyze the content of everything the mind conceives. For this purpose, any object of thought will do; it may be this desk before me, or the paper I write on, or the hand that does the writing, or even the gratification that comes over me when my thought meets perfect expression. I have but to pause to realize that all of these things or experiences are each of them some kind of being, and that if neither they nor anything else existed, I would have nothing to which to attach my thoughts - I would, indeed, have no thoughts. Even negations and privations are conceived in reference to being, after the manner of being. Take away being and no object of thought remains, and consequently no thought.
This conclusion is still more compelling from the analysis of judgment, the second operation of the mind, in which the act of understanding is completed. Essentially, judgment comprises a subject and another term that determines or qualifies the subject. The second term may take the form of a copula followed by a predicate, "the weather is pleasant," or it may simply be a verb, "the sun shines." In the first case the affirmation of being, that something is, is clear enough; but even in the second case being is truly affirmed, though implicitly. A judgment, then, is made in reference to what is, hence in reference to being. And this is true of every judgment, affirmative or negative; in one as in the other, there is an association of two terms telling of being, saying what it is or what it is not. Thus, in its perfective moment as well as in its first moment (first operation of the mind), every act of thought is determined by being and fixes on being. And since reality is being, to think is to form a conception of reality.
In summary: being is the first and most comprehensive object of thought. Since metaphysics is the science of what is first and most universal or comprehensive, its object, it follows, is being. However, the inner content of being, its metaphysical store, is not thereby told. We have therefore to probe the matter further.