Objection 1. It would seem that Word in God is not a personal name. For personal names are applied to God in a proper sense, as Father and Son. But Word is applied to God metaphorically, as Origen says on (John 1:1), "In the beginning was the Word." Therefore Word is not a personal name in God.
Objection 2. Further, according to Augustine (De Trin. ix, 10), "The Word is knowledge with love;" and according to Anselm (Monol. lx), "To speak is to the Supreme Spirit nothing but to see by thought." But knowledge and thought, and sight, are essential terms in God. Therefore Word is not a personal term in God.
Objection 3. Further, it is essential to word to be spoken. But, according to Anselm (Monol. lix), as the Father is intelligent, the Son is intelligent, and the Holy Ghost is intelligent, so the Father speaks, the Son speaks, and the Holy Ghost speaks; and likewise, each one of them is spoken. Therefore, the name Word is used as an essential term in God, and not in a personal sense.
Objection 4. Further, no divine person is made. But the Word of God is something made. For it is said, "Fire, hail, snow, ice, the storms which do His Word" (Psalm 148:8). Therefore the Word is not a personal name in God.
On the contrary, Augustine says (De Trin. vii, 11): "As the Son is related to the Father, so also is the Word to Him Whose Word He is." But the Son is a personal name, since it is said relatively. Therefore so also is Word.
I answer that, The name of Word in God, if taken in its proper sense, is a personal name, and in no way an essential name.
To see how this is true, we must know that our own word taken in its proper sense has a threefold meaning; while in a fourth sense it is taken improperly or figuratively. The clearest and most common sense is when it is said of the word spoken by the voice; and this proceeds from an interior source as regards two things found in the exterior word--that is, the vocal sound itself, and the signification of the sound. For, according to the Philosopher (Peri Herm. i) vocal sound signifies the concept of the intellect. Again the vocal sound proceeds from the signification or the imagination, as stated in De Anima ii, text 90. The vocal sound, which has no signification cannot be called a word: wherefore the exterior vocal sound is called a word from the fact the it signifies the interior concept of the mind. Therefore it follows that, first and chiefly, the interior concept of the mind is called a word; secondarily, the vocal sound itself, signifying the interior concept, is so called; and thirdly, the imagination of the vocal sound is called a word. Damascene mentions these three kinds of words (De Fide Orth. i, 17), saying that "word" is called "the natural movement of the intellect, whereby it is moved, and understands, and thinks, as light and splendor;" which is the first kind. "Again," he says, "the word is what is not pronounced by a vocal word, but is uttered in the heart;" which is the third kind. "Again," also, "the word is the angel"--that is, the messenger "of intelligence;" which is the second kind. Word is also used in a fourth way figuratively for that which is signified or effected by a word; thus we are wont to say, "this is the word I have said," or "which the king has commanded," alluding to some deed signified by the word either by way of assertion or of command.
Now word is taken strictly in God, as signifying the concept of the intellect. Hence Augustine says (De Trin. xv, 10): "Whoever can understand the word, not only before it is sounded, but also before thought has clothed it with imaginary sound, can already see some likeness of that Word of Whom it is said: In the beginning was the Word." The concept itself of the heart has of its own nature to proceed from something other than itself--namely, from the knowledge of the one conceiving. Hence "Word," according as we use the term strictly of God, signifies something proceeding from another; which belongs to the nature of personal terms in God, inasmuch as the divine persons are distinguished by origin (27, 3,4,5). Hence the term "Word," according as we use the term strictly of God, is to be taken as said not essentially, but personally.
Reply to Objection 1. The Arians, who sprang from Origen, declared that the Son differed in substance from the Father. Hence, they endeavored to maintain that when the Son of God is called the Word, this is not to be understood in a strict sense; lest the idea of the Word proceeding should compel them to confess that the Son of God is of the same substance as the Father. For the interior word proceeds in such a manner from the one who pronounces it, as to remain within him. But supposing Word to be said metaphorically of God, we must still admit Word in its strict sense. For if a thing be called a word metaphorically, this can only be by reason of some manifestation; either it makes something manifest as a word, or it is manifested by a word. If manifested by a word, there must exist a word whereby it is manifested. If it is called a word because it exteriorly manifests, what it exteriorly manifests cannot be called word except in as far as it signifies the interior concept of the mind, which anyone may also manifest by exterior signs. Therefore, although Word may be sometimes said of God metaphorically, nevertheless we must also admit Word in the proper sense, and which is said personally.
Reply to Objection 2. Nothing belonging to the intellect can be applied to God personally, except word alone; for word alone signifies that which emanates from another. For what the intellect forms in its conception is the word. Now, the intellect itself, according as it is made actual by the intelligible species, is considered absolutely; likewise the act of understanding which is to the actual intellect what existence is to actual being; since the act of understanding does not signify an act going out from the intelligent agent, but an act remaining in the agent. Therefore when we say that word is knowledge, the term knowledge does not mean the act of a knowing intellect, or any one of its habits, but stands for what the intellect conceives by knowing. Hence also Augustine says (De Trin. vii, 1) that the Word is "begotten wisdom;" for it is nothing but the concept of the Wise One; and in the same way It can be called "begotten knowledge." Thus can also be explained how "to speak" is in God "to see by thought," forasmuch as the Word is conceived by the gaze of the divine thought. Still the term "thought" does not properly apply to the Word of God. For Augustine says (De Trin. xv, 16): "Therefore do we speak of the Word of God, and not of the Thought of God, lest we believe that in God there is something unstable, now assuming the form of Word, now putting off that form and remaining latent and as it were formless." For thought consists properly in the search after the truth, and this has no place in God. But when the intellect attains to the form of truth, it does not think, but perfectly contemplates the truth. Hence Anselm (Monol. lx) takes "thought" in an improper sense for "contemplation."
Reply to Objection 3. As, properly speaking, Word in God is said personally, and not essentially, so likewise is to "speak." Hence, as the Word is not common to the Father, Son and Holy Ghost, so it is not true that the Father, Son, and Holy Ghost are one speaker. So Augustine says (De Trin. vii, 1): "He who speaks in that co-eternal Word is understood as not alone in God, but as being with that very Word, without which, forsooth, He would not be speaking." On the other hand, "to be spoken" belongs to each Person, for not only is the word spoken, but also the thing understood or signified by the word. Therefore in this manner to one person alone in God does it belong to be spoken in the same way as a word is spoken; whereas in the way whereby a thing is spoken as being understood in the word, it belongs to each Person to be spoken. For the Father, by understanding Himself, the Son and the Holy Ghost, and all other things comprised in this knowledge, conceives the Word; so that thus the whole Trinity is "spoken" in the Word; and likewise also all creatures: as the intellect of a man by the word he conceives in the act of understanding a stone, speaks a stone. Anselm took the term "speak" improperly for the act of understanding; whereas they really differ from each other; for "to understand" means only the habitude of the intelligent agent to the thing understood, in which habitude no trace of origin is conveyed, but only a certain information of our intellect; forasmuch as our intellect is made actual by the form of the thing understood. In God, however, it means complete identity, because in God the intellect and the thing understood are altogether the same, as was proved above (14, 4,5). Whereas to "speak" means chiefly the habitude to the word conceived; for "to speak" is nothing but to utter a word. But by means of the word it imports a habitude to the thing understood which in the word uttered is manifested to the one who understands. Thus, only the Person who utters the Word is "speaker" in God, although each Person understands and is understood, and consequently is spoken by the Word.
Reply to Objection 4. The term "word" is there taken figuratively, as the thing signified or effected by word is called word. For thus creatures are said to do the word of God, as executing any effect, whereto they are ordained from the word conceived of the divine wisdom; as anyone is said to do the word of the king when he does the work to which he is appointed by the king's word.
Source: Summa Theologica (New Advent)