essence usually means nothing else than substance in our language, that is, in Latin. And provided that what is said is understood only in a mystery, such a way of speaking was sufficient, in order that there might be something to say when it was asked what the three are, which the true faith pronounces to be three, when it both declares that the Father is not the Son, and that the Holy Spirit, which is the gift of God, is neither the Father nor the Son. When, then, it is asked what the three are, or who the three are, we betake ourselves to the finding out of some special or general name under which we may embrace these three; and no such name occurs to the mind, because the super-eminence of the Godhead surpasses the power of customary speech. For God is more truly thought than He is altered, and exists more truly than He is thought. For when we say that Jacob was not the same as Abraham, but that Isaac was neither Abraham nor Jacob, certainly we confess that they are three, Abraham, Isaac, and Jacob. But when it is asked what three, we reply three men, calling them in the plural by a specific name; but if we were to say three animals, then by a generic name; for man, as the ancients have defined him, is a rational, mortal animal: or again, as our Scriptures usually speak, three souls, since it is fitting to denominate the whole from the better part, that is, to denominate both body and soul, which is the whole man, from the soul; for so it is said that seventy-five souls went down into Egypt with Jacob, instead of saying so many men.  Again, when we say that your horse is not mine, and that a third belonging to some one else is neither mine nor yours, then we confess that there are three; and if any one ask what three, we answer three horses by a specific name, but three animals by a generic one. And yet again, when we say that an ox is not a horse, but that a dog is neither an ox nor a horse, we speak of a three; and if any one questions us what three, we do not speak now by a specific name of three horses, or three oxen, or three dogs, because the three are not contained under the same species, but by a generic name, three animals; or if under a higher genus, three substances, or three creatures, or three natures. But whatsoever things are expressed in the plural number specifically by one name, can also be expressed generically by one name. But all things which are generically called by one name cannot also be called specifically by one name. For three horses, which is a specific name, we also call three animals; but, a horse, and an ox, and a dog, we call only three animals or substances, which are generic names, or anything else that can be spoken generically concerning them; but we cannot speak of them as three horses, or oxen, or dogs, which are specific names; for we express those things by one name, although in the plural number, which have that in common that is signified by the name. For Abraham, and Isaac, and Jacob, have in common that which is man; therefore they are called three men: a horse also, and an ox, and a dog, have in common that which is animal; therefore they are called three animals. So three several laurels we also call three trees; but a laurel, and a myrtle, and an olive, we call only three trees, or three substances, or three natures: and so three stones we call also three bodies; but stone, and wood, and iron, we call only three bodies, or by any other higher generic name by which they can be called. Of the Father, therefore, the Son, and the Holy Spirit, seeing that they are three, let us ask what three they are, and what they have in common. For the being the Father is not common to them, so that they should be interchangeably fathers to one another: as friends, since they are so called relatively to each other, can be called three friends, because they are so mutually to each other. But this is not the case in the Trinity, since the Father only is there father; and not Father of two, but of the Son only. Neither are they three Sons, since the Father there is not the Son, nor is the Holy Spirit. Neither three Holy Spirits, because the Holy Spirit also, in that proper meaning by which He is also called the gift of God, is neither the Father nor the Son. What three therefore? For if three persons, then that which is meant by person is common to them; therefore this name is either specific or generic to them, according to the manner of speaking. But where there is no difference of nature, there things that are several in number are so expressed generically, that they can also be expressed specifically. For the difference of nature causes, that a laurel, and a myrtle, and an olive, or a horse, and an ox, and a dog, are not called by the specific name, the former of three laurels, or the latter of three oxen, but by the generic name, the former of three trees, and the latter of three animals. But here, where there is no difference of essence, it is necessary that these three should have a specific name, which yet is not to be found. For person is a generic name, insomuch that man also can be so called, although there is so great a difference between man and God.
8. Further, in regard to that very generic (generalis) word, if on this account we say three persons, because that which person means is common to them (otherwise they can in no way be so called, just as they are not called three sons, because that which son means is not common to them); why do we not also say three Gods? For certainly, since the Father is a person, and the Son a person, and the Holy Spirit a person, therefore there are three persons: since then the Father is God, and the Son God, and the Holy Spirit God, why not three Gods? Or else, since on account of their ineffable union these three are together one God, why not also one person; so that we could not say three persons, although we call each a person singly, just as we cannot say three Gods, although we call each singly God, whether the Father, or the Son, or the Holy Spirit? Is it because Scripture does not say three Gods? But neither do we find that Scripture anywhere mentions three persons. Or is it because Scripture does not call these three, either three persons or one person (for we read of the person of the Lord, but not of the Lord as a person), that therefore it was lawful through the mere necessity of speaking and reasoning to say three persons, not because Scripture says it, but because Scripture does not contradict it: whereas, if we were to say three Gods, Scripture would contradict it, which says, "Hear, O Israel; the Lord thy God is one God?"  Why then is it not also lawful to say three essences; which, in like manner, as Scripture does not say, so neither does it contradict? For if essence is a specific (specialis) name common to three, why are They not to be called three essences, as Abraham, Isaac, and Jacob are called three men, because man is the specific name common to all men? But if essence is not a specific name, but a generic one, since man, and cattle, and tree, and constellation, and angel, are called essences; why are not these called three essences, as three horses are called three animals, and three laurels are called three trees, and three stones three bodies? Or if they are not called three essences, but one essence, on account of the unity of the Trinity, why is it not the case, that on account of the same unity of the Trinity they are not to be called three substances or three persons, but one substance and one person? For as the name of essence is common to them, so that each singly is called essence, so the name of either substance or person is common to them. For that which must be understood of persons according to our usage, this is to be understood of substances according to the Greek usage; for they say three substances, one essence, in the same way as we say three persons, one essence or substance.
9. What therefore remains, except that we confess that these terms sprang from the necessity of speaking, when copious reasoning was required against the devices or errors of the heretics? For when human weakness endeavored to utter in speech to the senses of man what it grasps in the secret places of the mind in proportion to its comprehension respecting the Lord God its creator, whether by devout faith, or by any discernment whatsoever; it feared to say three essences, lest any difference should be understood to exist in that absolute equality. Again, it could not say that there were not three somewhats (tria quædam), for it was because Sabellius said this that he fell into heresy. For it must be devoutly believed, as most certainly known from the Scriptures, and must be grasped by the mental eye with undoubting perception, that there is both Father, and Son, and Holy Spirit; and that the Son is not the same with the Father, nor the Holy Spirit the same with the Father or the Son. It sought then what three it should call them, and answered substances or persons; by which names it did not intend diversity to be meant, but singleness to be denied: that not only unity might be understood therein from the being called one essence, but also Trinity from the being called three substances or persons. For if it is the same thing with God to be (esse) as to subsist (subsistere), they were not to be called three substances, in such sense as they are not called three essences; just as, because it is the same thing with God to be as to be wise, as we do not say three essences, so neither three wisdoms. For so, because it is the same thing to Him to be God as to be, it is not right to say three essences, as it is not right to say three Gods. But if it is one thing to God to be, another to subsist, as it is one thing to God to be, another to be the Father or the Lord (for that which He is, is spoken in respect to Himself, but He is called Father in relation to the Son, and Lord in relation to the creature which serves Him); therefore He subsists relatively, as He begets relatively, and bears rule relatively: so then substance will be no longer substance, because it will be relative. For as from being, He is called essence, so from subsisting, we speak of substance. But it is absurd that substance should be spoken relatively, for everything subsists in respect to itself; how much more God? 
 Bk. v. c. 28.  Deuteronomy 6:4  [Augustin's meaning is, that the term "substance" is not an adequate one whereby to denote a trinitarian distinction, because in order to denote such a distinction it must be employed relatively, while in itself it has an absolute signification. In the next chapter he proceeds to show this.--W.G.T.S.]
 Deuteronomy 6:4
 [Augustin's meaning is, that the term "substance" is not an adequate one whereby to denote a trinitarian distinction, because in order to denote such a distinction it must be employed relatively, while in itself it has an absolute signification. In the next chapter he proceeds to show this.--W.G.T.S.]