Objection 1. It would seem that the essential attributes are appropriated to the persons unfittingly by the holy doctors. For Hilary says (De Trin. ii): "Eternity is in the Father, the species in the Image; and use is in the Gift." In which words he designates three names proper to the persons: the name of the "Father," the name "Image" proper to the Son (35, 2), and the name "Bounty" or "Gift," which is proper to the Holy Ghost (38, 2). He also designates three appropriated terms. For he appropriates "eternity" to the Father, "species" to the Son, and "use" to the Holy Ghost. This he does apparently without reason. For "eternity" imports duration of existence; "species," the principle of existence; and 'use' belongs to the operation. But essence and operation are not found to be appropriated to any person. Therefore the above terms are not fittingly appropriated to the persons.
Objection 2. Further, Augustine says (De Doctr. Christ. i, 5): "Unity is in the Father, equality in the Son, and in the Holy Ghost is the concord of equality and unity." This does not, however, seem fitting; because one person does not receive formal denomination from what is appropriated to another. For the Father is not wise by the wisdom begotten, as above explained (37, 2, ad 1). But, as he subjoins, "All these three are one by the Father; all are equal by the Son, and all united by the Holy Ghost." The above, therefore, are not fittingly appropriated to the Persons.
Objection 3. Further, according to Augustine, to the Father is attributed "power," to the Son "wisdom," to the Holy Ghost "goodness." Nor does this seem fitting; for "strength" is part of power, whereas strength is found to be appropriated to the Son, according to the text, "Christ the strength [Douay: power] of God" (1 Corinthians 1:24). So it is likewise appropriated to the Holy Ghost, according to the words, "strength [Douay: virtue] came out from Him and healed all" (Luke 6:19). Therefore power should not be appropriated to the Father.
Objection 4. Likewise Augustine says (De Trin. vi, 10): "What the Apostle says, "From Him, and by Him, and in Him," is not to be taken in a confused sense." And (Contra Maxim. ii) "'from Him' refers to the Father, 'by Him' to the Son, 'in Him' to the Holy Ghost.'" This, however, seems to be incorrectly said; for the words "in Him" seem to imply the relation of final cause, which is first among the causes. Therefore this relation of cause should be appropriated to the Father, Who is "the principle from no principle."
Objection 5. Likewise, Truth is appropriated to the Son, according to John 14:6, "I am the Way, the Truth, and the Life"; and likewise "the book of life," according to Psalm 39:9, "In the beginning of the book it is written of Me," where a gloss observes, "that is, with the Father Who is My head," also this word "Who is"; because on the text of Isaiah 65:1, "Behold I go to the Gentiles," a gloss adds, "The Son speaks Who said to Moses, I am Who am." These appear to belong to the Son, and are not appropriated. For "truth," according to Augustine (De Vera Relig. 36), "is the supreme similitude of the principle without any dissimilitude." So it seems that it properly belongs to the Son, Who has a principle. Also the "book of life" seems proper to the Son, as signifying "a thing from another"; for every book is written by someone. This also, "Who is," appears to be proper to the Son; because if when it was said to Moses, "I am Who am," the Trinity spoke, then Moses could have said, "He Who is Father, Son, and Holy Ghost, and the Holy Ghost sent me to you," so also he could have said further, "He Who is the Father, and the Son, and the Holy Ghost sent me to you," pointing out a certain person. This, however, is false; because no person is Father, Son and Holy Ghost. Therefore it cannot be common to the Trinity, but is proper to the Son.
I answer that, Our intellect, which is led to the knowledge of God from creatures, must consider God according to the mode derived from creatures. In considering any creature four points present themselves to us in due order. Firstly, the thing itself taken absolutely is considered as a being. Secondly, it is considered as one. Thirdly, its intrinsic power of operation and causality is considered. The fourth point of consideration embraces its relation to its effects. Hence this fourfold consideration comes to our mind in reference to God.
According to the first point of consideration, whereby we consider God absolutely in His being, the appropriation mentioned by Hilary applies, according to which "eternity" is appropriated to the Father, "species" to the Son, "use" to the Holy Ghost. For "eternity" as meaning a "being" without a principle, has a likeness to the property of the Father, Who is "a principle without a principle." Species or beauty has a likeness to the property of the Son. For beauty includes three conditions, "integrity" or "perfection," since those things which are impaired are by the very fact ugly; due "proportion" or "harmony"; and lastly, "brightness" or "clarity," whence things are called beautiful which have a bright color.
The first of these has a likeness to the property of the Son, inasmuch as He as Son has in Himself truly and perfectly the nature of the Father. To insinuate this, Augustine says in his explanation (De Trin. vi, 10): "Where--that is, in the Son--there is supreme and primal life," etc.
The second agrees with the Son's property, inasmuch as He is the express Image of the Father. Hence we see that an image is said to be beautiful, if it perfectly represents even an ugly thing. This is indicated by Augustine when he says (De Trin. vi, 10), "Where there exists wondrous proportion and primal equality," etc.
The third agrees with the property of the Son, as the Word, which is the light and splendor of the intellect, as Damascene says (De Fide Orth. iii, 3). Augustine alludes to the same when he says (De Trin. vi, 10): "As the perfect Word, not wanting in anything, and, so to speak, the art of the omnipotent God," etc.
"Use" has a likeness to the property of the Holy Ghost; provided the "use" be taken in a wide sense, as including also the sense of "to enjoy"; according as "to use" is to employ something at the beck of the will, and "to enjoy" means to use joyfully, as Augustine says (De Trin. x, 11). So "use," whereby the Father and the Son enjoy each other, agrees with the property of the Holy Ghost, as Love. This is what Augustine says (De Trin. vi, 10): "That love, that delectation, that felicity or beatitude, is called use by him" (Hilary). But the "use" by which we enjoy God, is likened to the property of the Holy Ghost as the Gift; and Augustine points to this when he says (De Trin. vi, 10): "In the Trinity, the Holy Ghost, the sweetness of the Begettor and the Begotten, pours out upon us mere creatures His immense bounty and wealth." Thus it is clear how "eternity," "species," and "use" are attributed or appropriated to the persons, but not essence or operation; because, being common, there is nothing in their concept to liken them to the properties of the Persons.
The second consideration of God regards Him as "one." In that view Augustine (De Doctr. Christ. i, 5) appropriates "unity" to the Father, "equality" to the Son, "concord" or "union" to the Holy Ghost. It is manifest that these three imply unity, but in different ways. For "unity" is said absolutely, as it does not presuppose anything else; and for this reason it is appropriated to the Father, to Whom any other person is not presupposed since He is the "principle without principle." "Equality" implies unity as regards another; for that is equal which has the same quantity as another. So equality is appropriated to the Son, Who is the "principle from a principle." "Union" implies the unity of two; and is therefore appropriated to the Holy Ghost, inasmuch as He proceeds from two. And from this we can understand what Augustine means when he says (De Doctr. Christ. i, 5) that "The Three are one, by reason of the Father; They are equal by reason of the Son; and are united by reason of the Holy Ghost." For it is clear that we trace a thing back to that in which we find it first: just as in this lower world we attribute life to the vegetative soul, because therein we find the first trace of life. Now "unity" is perceived at once in the person of the Father, even if by an impossible hypothesis, the other persons were removed. So the other persons derive their unity from the Father. But if the other persons be removed, we do not find equality in the Father, but we find it as soon as we suppose the Son. So, all are equal by reason of the Son, not as if the Son were the principle of equality in the Father, but that, without the Son equal to the Father, the Father could not be called equal; because His equality is considered firstly in regard to the Son: for that the Holy Ghost is equal to the Father, is also from the Son. Likewise, if the Holy Ghost, Who is the union of the two, be excluded, we cannot understand the oneness of the union between the Father and the Son. So all are connected by reason of the Holy Ghost; because given the Holy Ghost, we find whence the Father and the Son are said to be united.
According to the third consideration, which brings before us the adequate power of God in the sphere of causality, there is said to be a third kind of appropriation, of "power," "wisdom," and "goodness." This kind of appropriation is made both by reason of similitude as regards what exists in the divine persons, and by reason of dissimilitude if we consider what is in creatures. For "power" has the nature of a principle, and so it has a likeness to the heavenly Father, Who is the principle of the whole Godhead. But in an earthly father it is wanting sometimes by reason of old age. "Wisdom" has likeness to the heavenly Son, as the Word, for a word is nothing but the concept of wisdom. In an earthly son this is sometimes absent by reason of lack of years. "Goodness," as the nature and object of love, has likeness to the Holy Ghost; but seems repugnant to the earthly spirit, which often implies a certain violent impulse, according to Isaiah 25:4: "The spirit of the strong is as a blast beating on the wall." "Strength" is appropriated to the Son and to the Holy Ghost, not as denoting the power itself of a thing, but as sometimes used to express that which proceeds from power; for instance, we say that the strong work done by an agent is its strength.
According to the fourth consideration, i.e. God's relation to His effects, there arise appropriation of the expression "from Whom, by Whom, and in Whom." For this preposition "from" [ex] sometimes implies a certain relation of the material cause; which has no place in God; and sometimes it expresses the relation of the efficient cause, which can be applied to God by reason of His active power; hence it is appropriated to the Father in the same way as power. The preposition "by" [per] sometimes designates an intermediate cause; thus we may say that a smith works "by" a hammer. Hence the word "by" is not always appropriated to the Son, but belongs to the Son properly and strictly, according to the text, "All things were made by Him" (John 1:3); not that the Son is an instrument, but as "the principle from a principle." Sometimes it designates the habitude of a form "by" which an agent works; thus we say that an artificer works by his art. Hence, as wisdom and art are appropriated to the Son, so also is the expression "by Whom." The preposition "in" strictly denotes the habitude of one containing. Now, God contains things in two ways: in one way by their similitudes; thus things are said to be in God, as existing in His knowledge. In this sense the expression "in Him" should be appropriated to the Son. In another sense things are contained in God forasmuch as He in His goodness preserves and governs them, by guiding them to a fitting end; and in this sense the expression "in Him" is appropriated to the Holy Ghost, as likewise is "goodness." Nor need the habitude of the final cause (though the first of causes) be appropriated to the Father, Who is "the principle without a principle": because the divine persons, of Whom the Father is the principle, do not proceed from Him as towards an end, since each of Them is the last end; but They proceed by a natural procession, which seems more to belong to the nature of a natural power.
Regarding the other points of inquiry, we can say that since "truth" belongs to the intellect, as stated above (Question 16, Article 1), it is appropriated to the Son, without, however, being a property of His. For truth can be considered as existing in the thought or in the thing itself. Hence, as intellect and thing in their essential meaning, are referred to the essence, and not to the persons, so the same is to be said of truth. The definition quoted from Augustine belongs to truth as appropriated to the Son. The "book of life" directly means knowledge but indirectly it means life. For, as above explained (24, 1), it is God's knowledge regarding those who are to possess eternal life. Consequently, it is appropriated to the Son; although life is appropriated to the Holy Ghost, as implying a certain kind of interior movement, agreeing in that sense with the property of the Holy Ghost as Love. To be written by another is not of the essence of a book considered as such; but this belongs to it only as a work produced. So this does not imply origin; nor is it personal, but an appropriation to a person. The expression "Who is" is appropriated to the person of the Son, not by reason of itself, but by reason of an adjunct, inasmuch as, in God's word to Moses, was prefigured the delivery of the human race accomplished by the Son. Yet, forasmuch as the word "Who" is taken in a relative sense, it may sometimes relate to the person of the Son; and in that sense it would be taken personally; as, for instance, were we to say, "The Son is the begotten 'Who is,'" inasmuch as "God begotten is personal." But taken indefinitely, it is an essential term. And although the pronoun "this" [iste] seems grammatically to point to a particular person, nevertheless everything that we can point to can be grammatically treated as a person, although in its own nature it is not a person; as we may say, "this stone," and "this ass." So, speaking in a grammatical sense, so far as the word "God" signifies and stands for the divine essence, the latter may be designated by the pronoun "this," according to Exodus 15:2: "This is my God, and I will glorify Him."
Source: Summa Theologica (New Advent)