In the chapter on being 1 we saw that the metaphysical notion of being, which is an analogous concept, embraces all reality in a proportional unity. We found, moreover, that the notion is a complex one, adverting in particular to the distinct aspects of essence and existence. We have now to consider some other aspects of being, its properties (as they are called), for the study of being as being should include whatever is inseparable from and convertible with being. This, of course, should logically be done before treating of the categories, particular modes of being.
Parenthetically, this further determination of being - finding its properties, the aspects or elements common to being as being - is not to be done in the manner of some idealists, by a dialectic of pure deduction; for from the mere notion of being we get - the mere notion of being. The properties of being are based in reality and must be sought there; indeed they are given, at least in principle, when being is given, in the mind's first apprehension. The question, then, is not one of drawing something from an abstraction, that is, from the abstract notion of being but rather from the reality of being, the same being which the mind first experiences. By redirecting its attention to the content of this experience the mind becomes explicitly aware of the properties of being and thus acquires a more integral conception of the reality which constitutes its initial datum.
Granted the necessity of recourse to experience for progress in metaphysical thought, we have still to determine how "anything" can be added to being. St. Thomas, in a classic passage, explains the point perfectly.2 Being, he says, cannot be diversified in the manner of a genus, by differences that would not be contained in being itself - a specific difference is not actually contained in a genus.3 Being can only be differentiated through modes which are intrinsic to being itself. Basically, there are but two ways for this differentiation to occur. Either the modes in question are particular modes, constituting the so-called predicaments of being; or they are modes which pertain to being universally and necessarily, to every being without exception. In St. Thomas' words,
nothing can be added to being as though it were something not included in being - in the way that a difference is added to a genus or an accident to a subject - for every reality is essentially a being. The Philosopher has shown this by proving that being cannot be a genus [Metaph.B,3, 993 b 23]. Yet, in this sense some predicates may be said to add to being, namely, inasmuch as they express a mode of being not expressed by the term being. This happens in two ways. First, the mode expressed is some particular manner of being; for there are different grades of being, according to which we speak of different modes of existence; and conformably to these modes the different genera of things are drawn up. . . . Second, something is said to add to being because the mode it expresses is one that is common and consequent upon every being. . . .4
These modes, "consequent upon every being," constitute, in the accepted parlance, the transcendental properties of being; of which severally in the course of the chapter. For the present, note that they are not "properties" in the strict sense, for then they would express something that is extrinsic to the nature of being, a manifest impossibility. They are therefore properties in a larger sense, as inseparable from being and designating it under another aspect. As for "transcendental," this they are in the same sense as being: that which occurs in all being, and so transcends any particular category of it. And because they are as universal as being itself, the transcendental modes are spoken of as convertible with being, so that in a proposition where being is the subject and one of the common modes the predicate (or vice versa), we may interchange them. If, for example, "being is one," then "the one is being," with no shift of meaning.