Boethius says (Com. Praed.) that the Greek {ousia}, which means essence, signifies a being composed of matter and form. Now that which is composed of matter and form is the individual substance called "hypostasis" and "person." Therefore all the aforesaid names seem to have the same meaning.
Objection 4: On the contrary, Boethius says (De Duab. Nat.) that genera and species only subsist; whereas individuals are not only subsistent, but also substand. But subsistences are so called from subsisting, as substance or hypostasis is so called from substanding. Therefore, since genera and species are not hypostases or persons, these are not the same as subsistences.
Objection 5: Further, Boethius says (Com. Praed.) that matter is called hypostasis, and form is called {ousiosis}---that is, subsistence. But neither form nor matter can be called person. Therefore person differs from the others.
I answer that, According to the Philosopher (Metaph. v), substance is twofold. In one sense it means the quiddity of a thing, signified by its definition, and thus we say that the definition means the substance of a thing; in which sense substance is called by the Greeks {ousia}, what we may call "essence." In another sense substance means a subject or "suppositum," which subsists in the genus of substance. To this, taken in a general sense, can be applied a name expressive of an intention; and thus it is called "suppositum." It is also called by three names signifying a reality---that is, "a thing of nature," "subsistence," and "hypostasis," according to a threefold consideration of the substance thus named. For, as it exists in itself and not in another, it is called "subsistence"; as we say that those things subsist which exist in themselves, and not in another. As it underlies some common nature, it is called "a thing of nature"; as, for instance, this particular man is a human natural thing. As it underlies the accidents, it is called "hypostasis," or "substance." What these three names signify in common to the whole genus of substances, this name "person" signifies in the genus of rational substances.
Reply to Objection 1: Among the Greeks the term "hypostasis," taken in the strict interpretation of the word, signifies any individual of the genus substance; but in the usual way of speaking, it means the individual of the rational nature, by reason of the excellence of that nature.
Reply to Objection 2: As we say "three persons" plurally in God, and "three subsistences," so the Greeks say "three hypostases." But because the word "substance," which, properly speaking, corresponds in meaning to "hypostasis," is used among us in an equivocal sense, since it sometimes means essence, and sometimes means hypostasis, in order to avoid any occasion of error, it was thought preferable to use "subsistence" for hypostasis, rather than "substance."
Reply to Objection 3: Strictly speaking, the essence is what is expressed by the definition. Now, the definition comprises the principles of the species, but not the individual principles. Hence in things composed of matter and form, the essence signifies not only the form, nor only the matter, but what is composed of matter and the common form, as the principles of the species. But what is composed of this matter and this form has the nature of hypostasis and person. For soul, flesh, and bone belong to the nature of man; whereas this soul, this flesh and this bone belong to the nature of this man. Therefore hypostasis and person add the individual principles to the idea of essence; nor are these identified with the essence in things composed of matter and form, as we said above when treating of divine simplicity ( Question [3], Article [3]).
Reply to Objection 4: Boethius says that genera and species subsist, inasmuch as it belongs to some individual things to subsist, from the fact that they belong to genera and species comprised in the predicament of substance, but not because the species and genera themselves subsist; except in the opinion of Plato, who asserted that the species of things subsisted separately from singular things. To substand, however, belongs to the same individual things in relation to the accidents, which are outside the essence of genera and species.
Reply to Objection 5: The individual composed of matter and form substands in relation to accident from the very nature of matter. Hence Boethius says (De Trin.): "A simple form cannot be a subject." Its self-subsistence is derived from the nature of its form, which does not supervene to the things subsisting, but gives actual existence to the matter and makes it subsist as an individual. On this account, therefore, he ascribes hypostasis to matter, and {ousiosis}, or subsistence, to the form, because the matter is the principle of substanding, and form is the principle of subsisting.
Whether the word "person" should be said of God?
Objection 1: It would seem that the name "person" should not be said of God. For Dionysius says (Div. Nom.): "No one should ever dare to say or think anything of the supersubstantial and hidden Divinity, beyond what has been divinely expressed to us by the oracles." But the name "person" is not expressed to us in the Old or New Testament. Therefore "person" is not to be applied to God.
Objection 2: Further, Boethius says (De Duab. Nat.): "The word person seems to be taken from those persons who represented men in comedies and tragedies. For person comes from sounding through [personando], since a greater volume of sound is produced through the cavity in the mask. These "persons" or masks the Greeks called {prosopa}, as they were placed on the face and covered the features before the eyes." This, however, can apply to God only in a metaphorical sense. Therefore the word "person" is only applied to God metaphorically.
Objection 3: Further, every person is a hypostasis. But the word "hypostasis" does not apply to God, since, as Boethius says (De Duab. Nat.), it signifies what is the subject of accidents, which do not exist in God. Jerome also says (Ep. ad Damas.) that, "in this word hypostasis, poison lurks in honey." Therefore the word "person" should not be said of God.
Objection 4: Further, if a definition is denied of anything, the thing defined is also denied of it. But the definition of "person," as given above, does not apply to God. Both because reason implies a discursive knowledge, which does not apply to God, as we proved above ( Question [14], Article [12]); and thus God cannot be said to have "a rational nature." And also because God cannot be called an individual substance, since the principle of individuation is matter; while God is immaterial: nor is He the subject of accidents, so as to be called a substance. Therefore the word "person" ought not to be attributed to God.
On the contrary, In the Creed of Athanasius we say: "One is the person of the Father, another of the Son, another of the Holy Ghost."
I answer that, "Person" signifies what is most perfect in all nature---that is, a subsistent individual of a rational nature. Hence, since everything that is perfect must be attributed to God, forasmuch as His essence contains every perfection, this name "person" is fittingly applied to God; not, however, as it is applied to creatures, but in a more excellent way; as other names also, which, while giving them to creatures, we attribute to God; as we showed above when treating of the names of God ( Question [13], Article [2]).
Reply to Objection 1: Although the word "person" is not found applied to God in Scripture, either in the Old or New Testament, nevertheless what the word signifies is found to be affirmed of God in many places of Scripture; as that He is the supreme self-subsisting being, and the most perfectly intelligent being. If we could speak of God only in the very terms themselves of Scripture, it would follow that no one could speak about God in any but the original language of the Old or New Testament. The urgency of confuting heretics made it necessary to find
