In his SEP article, The Medieval Problem of Universals, Gyula Klima offers the following explanation of the Thomistic doctrine of common natures:
So, a common nature or essence according to its absolute consideration abstracts from all existence, both in the singulars and in the mind. Yet, and this is the important point, it is the same nature that informs both the singulars that have this nature and the minds conceiving of them in terms of this nature. To be sure, this sameness is not numerical sameness, and thus it does not yield numerically one nature. On the contrary, it is the sameness of several, numerically distinct realizations of the same information-content, just like the sameness of a book in its several copies. Just as there is no such a thing as a universal book over and above the singular copies of the same book, so there is no such a thing as a universal nature existing over and above the singular things of the same nature; still, just as it is true to say that the singular copies are the copies of the same book, so it is true to say that these singulars are of the same nature.
I am struggling to understand this. Consider the common nature humanity. When we consider it in itself, or absolutely, we abstract from its existence in material singulars (Socrates, Plato, Aristotle, . . .) and from its existence in minds. When we consider it absolutely we thus consider it in abstraction from esse, whether esse naturale or esse intentionale. So considered, the common nature has no mode of esse or existence. Having no mode of existence, the common nature does not exist. This prompts my first question:
Q1. How can an item have no being or existence at all? (I am using 'being' and 'existence' interchangeably.) Would it not then be nothing? But it is not nothing; it is the very common nature that it is, one distinct from other common natures. What we have here, as it seems to me, is an anticipation of Meinong's doctrine of Aussersein, with the problems that the latter brings in its train. But having invoked Meinong I now send him back to his jungle; my present concern is merely to understand Aquinas. There is this item, humanity, which, absolutely considered, has no being, but is nonethless a definite mind-independent item. Mind-independent yet beingless. Do you not find this puzzling?
I am not suggesting that there is a narrowly-logical (purely formal) contradiction in There is an item that has no being. Some will be tempted to mount that objection since the italicized sentence certainly does smack of formal-logical contradiction: There is an x such that x is not. But the formal-logical contradiction seems to dissipate if we put it like this: Some item is beingless, where 'some' has no existential or ontological import whatsoever. The latter italicized sentence is not formally self-contradictory. Its form is Some F is G which admits of true substitution-instances.
So I see no formal-logical contradiction in the doctrine of common natures any more than I see a formal-logical contradiction in Meinong's doctrine of Aussersein. My point is not formal-logical but metaphysical. I just don't understand how something can be mind-independent without having any being at all.
Note also that this item -- humanity as common nature or natura absoluta -- is neither particular nor universal. It would be particular if it existed with esse naturale in singulars; it would be universal if it existed with esse intentionale in a mind. But in itself, considered absolutely, it exists in neither way and is therefore neither particular nor universal. This prompts my second question:
Q2. How can a nature be common and yet not in some sense universal? There is this item which we are considering in abstraction from its material existence in singulars and from its immaterial existence in minds. It seems that what we must say that it is universal, not particular. After all, it is common. How can an item be common to many (to many material singulars and to many acts of thinking) without being universal?
These are not rhetorical questions. I really don't understand the doctrine. (Some people have the unpleasant habit of accusing one of posing rhetorical questions when one genuinely asks questions. Isn't that what philosophers mainly do, ask questions?)
What's more, common natures are neither one nor many. In De Ente et Essentia, Thomas gives an argument for this claim, an argument I examine and reject in a separate post. At the moment I am concerned with the intelligibility of the claim, not its justification. I want to understand the claim, but so far I am finding it unintelligible. Hence my third question:
Q3. How can a common nature be neither one nor many? Must it not be one item to be common?
Klima offers an analogy. It is a commonplace that there can be many copies of the same book. Each copy is a material singular. And of course 'same book' does not refer to a material singular over and above the many copies. And yet the same information-content is expressed in each (uncorrupted) copy and is understood by each mind that reads (with comprehension) a copy. A common nature, then, is like the information-content of a book.
Unfortunately, this analogy does not help me. It seems obvious to me that the information-content is one, not neither one nor many.
To sum up. A common nature, considered absolutely, is neither one nor many, neither universal nor particular. Considered absolutely, it exists neither in singulars nor in minds. What's more, this absolute consideration, this consideration of it as it is in itself, does not make of it an abstractum that depends on a mind for its existence. And so it has some sort of mind-independent status along with its matter-independent status. Having neither esse naturale nor esse inentionale, it has no being at all. Having no being at all, we can say that common natures are ausserseiend in Meinong's sense, jenseits von Sein und Nichtsein, "beyond being and nonbeing." Each of these items is a pure Sosein with no Sein.
Is this a coherent conception? I can't see that it is. But I don't claim to have refuted it. For my misgivings rest on an assumption that, while it seems intuitively obvious to me, I would be hard-pressed to justify in a non-circular way,, namely, that whatever has mind-independent status must have some mode of being or other.