The second motive is because one person in God is related to two persons---namely, the person of the Father to the person of the Son and the person of the Holy Ghost. This is not, however, by one relation; otherwise it would follow that the Son also and the Holy Ghost would be related to the Father by one and the same relation. Thus, since relation alone multiplies the Trinity, it would follow that the Son and the Holy Ghost would not be two persons. Nor can it be said with Prepositivus that as God is related in one way to creatures, while creatures are related to Him in divers ways, so the Father is related by one relation to the Son and to the Holy Ghost; whereas these two persons are related to the Father by two relations. For, since the very specific idea of a relation is that it refers to another, it must be said that two relations are not specifically different if but one opposite relation corresponds to them. For the relation of lord and father must differ according to the difference of filiation and servitude. Now, all creatures are related to God as His creatures by one specific relation. But the Son and the Holy Ghost are not related to the Father by one and the same kind of relation. Hence there is no parity.
Further, in God there is no need to admit any real relation to the creature (Q[28], A[1],3); while there is no reason against our admitting in God, many logical relations. But in the Father there must be a real relation to the Son and to the Holy Ghost. Hence, corresponding to the two relations of the Son and of the Holy Ghost, whereby they are related to the Father, we must understand two relations in the Father, whereby He is related to the Son and to the Holy Ghost. Hence, since there is only one Person of the Father, it is necessary that the relations should be separately signified in the abstract; and these are what we mean by properties and notions.
Reply to Objection 1: Although the notions are not mentioned in Holy Scripture, yet the persons are mentioned, comprising the idea of notions, as the abstract is contained in the concrete.
Reply to Objection 2: In God the notions have their significance not after the manner of realities, but by way of certain ideas whereby the persons are known; although in God these notions or relations are real, as stated above (Q[28], A[1]). Therefore whatever has order to any essential or personal act, cannot be applied to the notions; forasmuch as this is against their mode of signification. Hence we cannot say that paternity begets, or creates, or is wise, or is intelligent. The essentials, however, which are not ordered to any act, but simply remove created conditions from God, can be predicated of the notions; for we can say that paternity is eternal, or immense, or such like. So also on account of the real identity, substantive terms, whether personal or essential, can be predicated of the notions; for we can say that paternity is God, and that paternity is the Father.
Reply to Objection 3: Although the persons are simple, still without prejudice to their simplicity, the proper ideas of the persons can be abstractedly signified, as above explained.
Whether there are five notions?
Objection 1: It would seem that there are not five notions. For the notions proper to the persons are the relations whereby they are distinguished from each other. But the relations in God are only four (Q[28], A[4]). Therefore the notions are only four in number.
Objection 2: Further, as there is only one essence in God, He is called one God, and because in Him there are three persons, He is called the Trine God. Therefore, if in God there are five notions, He may be called quinary; which cannot be allowed.
Objection 3: Further, if there are five notions for the three persons in God, there must be in some one person two or more notions, as in the person of the Father there is innascibility and paternity, and common spiration. Either these three notions really differ, or not. If they really differ, it follows that the person of the Father is composed of several things. But if they differ only logically, it follows that one of them can be predicated of another, so that we can say that as the divine goodness is the same as the divine wisdom by reason of the common reality, so common spiration is paternity; which is not to be admitted. Therefore there are not five notions.
Objection 4: On the contrary, It seems that there are more; because as the Father is from no one, and therefrom is derived the notion of innascibility; so from the Holy Ghost no other person proceeds. And in this respect there ought to be a sixth notion.
Objection 5: Further, as the Father and the Son are the common origin of the Holy Ghost, so it is common to the Son and the Holy Ghost to proceed from the Father. Therefore, as one notion is common to the Father and the Son, so there ought to be one notion common to the Son and to the Holy Ghost.
I answer that, A notion is the proper idea whereby we know a divine Person. Now the divine persons are multiplied by reason of their origin: and origin includes the idea of someone from whom another comes, and of someone that comes from another, and by these two modes a person can be known. Therefore the Person of the Father cannot be known by the fact that He is from another; but by the fact that He is from no one; and thus the notion that belongs to Him is called "innascibility." As the source of another, He can be known in two ways, because as the Son is from Him, the Father is known by the notion of "paternity"; and as the Holy Ghost is from Him, He is known by the notion of "common spiration." The Son can be known as begotten by another, and thus He is known by "filiation"; and also by another person proceeding from Him, the Holy Ghost, and thus He is known in the same way as the Father is known, by "common spiration." The Holy Ghost can be known by the fact that He is from another, or from others; thus He is known by "procession"; but not by the fact that another is from Him, as no divine person proceeds from Him.
Therefore, there are Five notions in God: "innascibility," "paternity," "filiation," "common spiration," and "procession." Of these only four are relations, for "innascibility" is not a relation, except by reduction, as will appear later (Q[33], A[4], ad 3). Four only are properties. For "common spiration" is not a property; because it belongs to two persons. Three are personal notions---i.e. constituting persons, "paternity," "filiation," and "procession." "Common spiration" and "innascibility" are called notions of Persons, but not personal notions, as we shall explain further on (Q[40], A[1], ad 1).
Reply to Objection 1: Besides the four relations, another notion must be admitted, as above explained.
Reply to Objection 2: The divine essence is signified as a reality; and likewise the persons are signified as realities; whereas the notions are signified as ideas notifying the persons. Therefore, although God is one by unity of essence, and trine by trinity of persons, nevertheless He is not quinary by the five notions.
Reply to Objection 3: Since the real plurality in God is founded only on relative opposition, the several properties of one Person, as they are not relatively opposed to each other, do not really differ. Nor again are they predicated of each other, because they are different ideas of the persons; as we do not say that the attribute of power is the attribute of knowledge, although we do say that knowledge is power.
Reply to Objection 4: Since Person implies dignity, as stated above (Q[19], A[3] ) we cannot derive a notion of the Holy Spirit from the fact that no person is from Him. For this does not belong to His dignity, as it belongs to the authority of the Father that He is from no one.
Reply to Objection 5: The Son and the Holy Ghost do not agree in one special mode of existence derived from the Father; as the Father and the Son agree in one special mode of producing the Holy Ghost. But the principle on which a notion is based must be something special; thus no parity of reasoning exists.
Whether it is lawful to have various contrary opinions of notions?
Objection 1: It would seem that it is not lawful to have various contrary opinions of the notions. For Augustine says (De Trin. i, 3): "No error is more dangerous than any as regards the Trinity": to which mystery the notions assuredly belong. But contrary opinions must be in some way erroneous. Therefore it is not right to have contrary opinions of the notions.
Objection 2: Further, the persons are known by the notions. But no contrary opinion concerning the persons is to be tolerated. Therefore neither can there be about the notions.
On the contrary, The notions are not articles of faith. Therefore different opinions of the notions are permissible.
I answer that, Anything is of faith in two ways; directly, where any truth comes to us principally as divinely taught, as the trinity and unity of God, the Incarnation of the Son, and the like; and concerning these truths a false opinion of itself involves heresy, especially if it be held obstinately. A thing is of faith, indirectly, if the denial of it involves as a consequence something against faith; as for instance if anyone said that Samuel was not the son of Elcana, for it follows that the divine Scripture would be false. Concerning such things anyone may have a false opinion without danger of heresy, before the matter has been considered or settled as involving consequences against faith, and particularly if no obstinacy be shown; whereas when it is manifest, and especially if the Church has decided that consequences follow against faith, then the error cannot be free from heresy. For this reason many things are now considered as heretical which were formerly not so considered, as their consequences are now more manifest.
So we must decide that anyone may entertain contrary opinions about the notions, if he does not mean to uphold anything at variance with faith. If, however, anyone should entertain a false opinion of the notions, knowing or thinking that consequences against the faith would follow, he would lapse into heresy.
By what has been said all the objections may be solved.