About the Work
The Tractatus de unitate et trinitate divina is a theological treatise on the doctrine of the Holy Trinity, written by the twelfth-century philosopher and theologian Peter Abelard. The work, whose title translates as A Treatise on the Unity and Trinity of God, is a systematic examination of one of the most contested doctrines in Christian theology: how God can be simultaneously one in substance and three in persons. The treatise is organized into three books, each addressing a distinct aspect of the Trinitarian question. The first book gathers testimonies from prophets, philosophers, and other authorities to establish the faith of the Holy Trinity. The second book presents the theme of the unity of divine substance and the trinity of persons, followed by a series of objections and their solutions. The third book continues the logical analysis of terms applied to God, addressing sophisms about predication and the proper way to speak of the divine persons.
The text survives in a twelfth-century parchment miscellany codex held at the Erlangen University Library, consisting of 107 leaves and originating from the Cistercian abbey of Heilsbronn. The codex contains several works: Boethius’s De sancta trinitate, the Abelard tract under the title Capitula librorum de trinitate, an anonymous commentary on Boethius, and the Athanasian Symbolum with commentary. The tract itself spans folios 27r through 65v of the codex. The manuscript title, Capitula librorum de trinitate, reflects the work’s content as a set of chapters or headings concerning the Trinity, while the second book’s summary is described as the “summam fidei circa unitatem ac trinitatem,” or the sum of faith concerning unity and trinity.
The work is closely connected to a significant event in Abelard’s life: the condemnation of a treatise on the Trinity at the Synod of Soissons in 1121. The editor of the text argues at length that the manuscript tract found at Erlangen is precisely the work that was condemned and burned at that synod. This identification rests on several lines of evidence, including the title of the work, its content matching accusations raised at the synod, and its small size, which would justify calling it an opusculum or little work. The treatise is also shown to be directed against Roscellin, a contemporary theologian whose Trinitarian views Abelard opposed. The work represents an early stage in Abelard’s theological development, later revised and expanded into the Theologia christiana, which itself was followed by the Introductio ad theologiam condemned at the Council of Sens in 1141.
Context
The treatise emerges from the intellectual ferment of the early twelfth century, a period marked by intense debate over the proper method of doing theology and the relationship between faith and reason. Abelard was a central figure in these debates, known for his application of dialectical method to theological questions. The work must be understood against the backdrop of several controversies that shaped Abelard’s career and the reception of his ideas.
The most immediate context is the condemnation at Soissons in 1121. According to the accounts of St. Bernard and Otto of Freising, the synod condemned Abelard’s work on the Trinity for Sabellianism—the heresy that collapses the distinction between the three divine persons, making them mere modes or aspects of one God. Otto of Freising specifically remarked that Abelard weakened the distinctness of the three persons, “nimis attenuans non bonis usus exemplis,” or excessively attenuating them with poorly chosen examples. The synod took place in March or April of 1121, and the work was publicly burned. Abelard’s own account in his Historia calamitatum describes the events, including the specific accusations raised against him. One accusation, raised by a certain Alberich, concerned a passage Abelard had cited from Augustine’s De trinitate; this passage appears verbatim in the manuscript tract. Another accusation, raised at the burning itself, charged that Abelard had taught that only God the Father is omnipotent; two passages in the tract, not carried into the later Theologia christiana, would support this charge.
The work is also situated within Abelard’s ongoing conflict with Roscellin, a nominalist theologian who held controversial views on the Trinity. From a letter of Roscellin discovered by Schmeller, it is known that Abelard had written to the church of St. Martin of Tours, where Roscellin was a canon, containing personal abuse and a refutation of Roscellin’s Trinitarian doctrine. The manuscript tract shares many points with this refutation, suggesting it may be the very work Abelard sent or a closely related text. The treatise thus participates in a broader theological controversy over how to conceptualize the Trinity without falling into tritheism (three separate gods) on the one hand or Sabellianism (three mere modes of one God) on the other.
The work also reflects the broader intellectual context of the twelfth-century renaissance, with its renewed interest in classical philosophy, particularly Plato and Aristotle. Abelard engages extensively with Platonic thought, citing the Timaeus and discussing Plato’s views on the world-soul. He also draws on the Peripatetic tradition, engaging with the logical works of Aristotle, Porphyry, and Boethius. The treatise is notable for its attempt to bring philosophical reasoning to bear on theological mysteries, a project that was controversial in its own time and contributed to Abelard’s condemnation. The editor notes that the work was written at a time when miracles had passed and malice had grown, so that the faithful “must fight with words” rather than deeds, trusting in the truth that says, “I will give you a mouth and wisdom.” This sense of intellectual combat against heresy and sophistry pervades the treatise.
Structure of the Book
The treatise is organized into three books, each with a distinct focus and argumentative strategy. The work as a whole follows a progression from the gathering of authorities, through the presentation of the doctrine and the answering of objections, to the resolution of logical difficulties in speaking about the Trinity.
The first book is devoted to collecting testimonies from prophets, philosophers, and other authorities to establish the faith of the Holy Trinity. The author states that since all controversy is either in writing or in reason, he deemed it opportune to bring authorities from the writings of excellent wise men and to support them with reasons where they seem irrationally attacked. This book draws on a wide range of sources. David, called the greatest of prophets and kings, is cited extensively for his superior intelligence and his teaching on the Trinity. Passages from the Psalms are interpreted to show the distinction of persons and the unity of substance. For instance, “Verbo domini caeli firmati sunt, et spiritu oris eius omnis virtus eorum” is read as teaching the distinction of the Trinity, while “Benedicat nos deus, deus noster, benedicat nos deus” is read as expressing the Trinity of persons through its threefold confession. The Psalmist’s use of the singular “eum” rather than the plural “eos” after the threefold naming is taken to open the unity of divine substance. Isaiah’s vision of the Seraphim crying “Sanctus, sanctus, sanctus dominus deus Sabaoth” is also cited as consonant with Trinitarian faith. The book also introduces philosophical witnesses, most notably Plato, whose statements in the Timaeus about the world-soul are interpreted as anticipating Christian teaching about the Holy Spirit. Augustine is cited extensively, including his observation in the City of God that some Christians marveled that Plato thought things congruent with our religion, and his account in the Confessions of reading in Platonic books that “In principio erat verbum, et verbum erat apud deum, et deus erat verbum.” The Sibyl is introduced as a female witness, though the passage breaks off before her testimony is fully presented.
The second book begins with a citation about Titus, son of Vespasian, who after avenging the blood of the Lord by subverting Jerusalem, entered Rome as a victor and was said to be of such goodness that he declared, “O friends, I have lost this day,” when he recalled having done no good that day. The author contrasts this with the failure to perceive the loss of hours, days, and moments when speaking idle words. The book then states its program: the author has gathered testimonies of prophets and philosophers, and now deems it opportune to bring authorities and support them with reasons. Against pseudo-dialecticians who seek the faith of the Trinity too subtly, the author condemns not the science of dialectic but the fallacy of sophistry, citing Augustine’s praise of dialectic. The book presents the theme of the unity of divine substance and trinity of persons, then lists fifteen objections against the Trinity, and then proceeds to answer them. The objections concern such matters as whether the Trinity is eternal if diversity is only in words, whether distinction follows the number of names, whether God would be trinus in substance if diversity is in the thing, how there can be three persons where there are not three things, and how Father and Son can be “such as” each other without similarity requiring discrete things. The book then develops the argument that God cannot be contained in the Peripatetic categories, since the divine substance is free from all accidents and all participation in form. The discussion of the modes of “same” and “diverse” is introduced, distinguishing several senses of these terms.
The third book continues the logical analysis of terms applied to God, addressing sophisms about predication. It argues that various inferences do not follow: if something is “twenty-one” or “twenty,” it does not follow that it is “one”; a half or imperfect house is not thereby a house; a “laughing meadow” is not thereby laughing; a “great thief” is not thereby great; being “good according to opinion” does not make one good; the Word being “made flesh” does not mean it is “made” simply; God being “made a helper” does not mean He is made; a “simple proposition” is not simple in the sense of having no parts at all; dispersed things forming “one multitude” are not thereby one; and the soul being “many persons” or “many places” according to dialecticians does not make it many. The book applies these distinctions to the Trinity, arguing that God is “many persons” but not “many things” or “many essences,” since the same essence that is the Father is also the Son and the Holy Spirit. The discussion addresses whether the trinity is a whole with parts, arguing that philosophical authority takes “part” in quantity, which is not in God. The book concludes with a discussion of how to understand statements like “such as the Father, such the Son,” arguing that similarity here means “not diverse in any good of majesty” and that “equal” means “in no way less in divinity.”
Detailed Section-by-Section Summary
The Discovery of the Soissons Tract at Erlangen
The editor opens by acknowledging that despite the vast scholarly attention devoted to Peter Abelard, significant problems regarding his principal dogmatic writings remain unresolved. Scholars have long disagreed, with figures like Denifle cited, over the identity of the work known as the Introductio ad theologiam. The central question was whether this text was the tract condemned at the Council of Soissons in 1121, the Theologia condemned at the Council of Sens in 1141, or merely a fragment of the latter. Further disagreement persisted over the chronological relationship between the Introductio ad theologiam and the Theologia christiana. The editor states that this issue is now settled on two main points: first, that the Introductio ad theologiam is indeed the work censured at Sens in 1141, a conclusion convincingly proven by Goldhorn and fortified by Denifle; and second, that the Theologia christiana was composed before the Introductio. While Goldhorn held the Theologia christiana to be the tract condemned at Soissons, a different hypothesis was advanced by Cousin and Deutsch. They maintained that the 1121 Soissons-condemned writing is lost, implying that Abelard wrote three distinct dogmatic works: the original 1121 tract, the Theologia christiana as a second, improved edition defending the first, and the later Introductio ad theologiam censured in 1141. The editor calls this a hypothesis requiring new manuscript evidence to be confirmed. He announces that he has found such evidence: he has discovered the Soissons-condemned tract at the Erlangen University Library, a find that brilliantly confirms the conjecture of Cousin and Deutsch. This discovery is presented as his third major scholarly find, following his identification of a Würzburg manuscript as a work of Konrad von Hirschau and his investigations into Giordano Bruno.
The Erlangen Codex and the Relationship of the Texts
The editor describes the physical evidence: the Erlangen library holds a 12th-century parchment miscellany codex of 107 leaves, originating from the Cistercian abbey of Heilsbronn. The codex contains four items: Boethius’s De sancta trinitate (fol. 1r–26r); a work titled Petri abaelardi capitula librorum de trinitate (fol. 27r–65v); an anonymous commentary on Boethius (fol. 66r–103v); and the Athanasian Symbolum with a commentary (fol. 103v–106v). The tract itself has three books. The editor establishes a structural correspondence: Book I of the tract corresponds to books 1–2 of the Theologia christiana; Book II corresponds to book 3; and Book III corresponds to book 4. A fifth book in the Theologia christiana is entirely new. The editor firmly rejects the possibility that the tract is an epitome or a shortened version of the Theologia christiana. He argues that Abelard would not have re-edited his own work in a shortened form, and that the pattern of omissions and additions that an epitomator would have made creates insoluble difficulties. For instance, fol. 48v–49r of the tract is an expansion, and fol. 50r replaces the phrase idem et diversum proprietate with idem et diversum effectu, which would be a strange alteration for a summarizer to make. Instead, the editor argues, the tract is the original work, and the Theologia christiana is a later reworking, characterized by additions, expansions, and relocations of material. A key proof of this chronological order lies in a textual detail: the tract (fol. 35r) reads “quid murmurent” (present tense), while the Theologia christiana (448 C 12–13) reads “quid murmurarint” (perfect tense). This shift in tense alludes to past events—specifically, the Synod of Soissons—as Abelard himself describes in his Historia calamitatum with the phrase “Quidam de adversariis meis id submurmuravit.” Furthermore, additions found in the Theologia christiana (e.g., 406 C 11 ff.) explicitly refer to defending his faith against “invidia sive erronea criminatione,” which points directly to his condemnation at Soissons. The editor notes his disagreement with Goldhorn, who failed to see this reference.
Further Evidence of Later Composition
The editor continues to marshal evidence that the Theologia christiana is the later work. He points to specific passages at 447 C 16–29 and 464 C 20–465 C 5. In the first, Abelard’s words “Unde et nos primum huic tanto periculo tam auctoritatum quam rationum clypeum opponere curavimus” indicate his earlier involvement in the question of the Trinity, and the following words, “in eo quidem confisi qui suos confortat…”, hint at his similar situation of facing danger before the papal legate at Soissons. In the second passage, Abelard’s bitter words, “In quo quidem si, culpis meis exigentibus…”, imply that he had already been judged not by his sincera intentio and had undergone a correction that was not grounded in reason or scriptural authority. The editor interprets this double injustice as a clear reference to the condemnation at Soissons. Crucially, these cited passages are absent from the manuscript tract, which supports their status as later additions and thus confirms the later composition of the Theologia christiana. The editor also identifies several marked additions in the Theologia christiana (e.g., 365 C 10–368 C 11) where Abelard defends a specific teaching against earlier misinterpretations—namely, the charge raised at Soissons that he taught “solum deum patrem omnipotentem esse” (as recorded in the Historia calamitatum). Another addition at 476 C 18–477 C 14 follows the very passage that was suspected by Alberich at Soissons, and the addition at 498 C 17–499 C 31 is explained in a similar fashion. The conclusion is that the Theologia christiana is a later reworking of an earlier theological writing, which is identified as the tract condemned at Soissons. The proof of this identity is deferred to the next chapter.
The Tract as the Work Condemned at Soissons
The editor now turns to proving that the manuscript tract 229 is the work condemned at Soissons in 1121. He first gathers general notices from external sources. St. Bernard (Migne 182, epist. 191, 193, 331) and Otto of Freising (Pertz, Mon. S.S. XX, p. 377, Gesta Friderici I, cap. 47) both report that the condemnation was for Sabellianism, a heresy that conflates the persons of the Trinity. The synod took place in March or April of 1121. Abelard himself, in his Historia calamitatum (C I, S. 18–19), calls the work “quemdam theologiae tractatum de unitate et trinitate divina” and “opus… quod de trinitate composueram.” In a letter to Gilbert, Bishop of Paris (C II, S. 151), written before the synod, he refers to it as “opusculo quodam nostro de fide sanctae trinitatis.” The manuscript tract’s own title is “Capitula librorum de trinitate” (fol. 27r), and its book II summary is “summam fidei circa unitatem ac trinitatem.” Fol. 39v gives the theme as “de unitate… divinae substantiae ac trinitate personarum.” The editor notes that the work may be called an opusculum due to its small size. He then addresses the two accusations raised at Soissons. The first, by Alberich, was answered by Abelard citing Augustine (De trinitate lib. I): “Qui putat — gignat” (C I, S. 19). This citation is found verbatim in the tract at fol. 44v and 45r. The second accusation, formulated at the burning of the book by an unnamed opponent, was: “Quod in libro scriptum deprehenderat solum deum patrem omnipotentem esse” (C I, S. 22). The editor finds two passages in the tract (fol. 53r and fol. 53r–v) that would support this charge, and notably, these passages were not carried over into the Theologia christiana. Furthermore, Otto of Freising’s remark that Abelard weakened the distinctness of the three persons “nimis attenuans non bonis usus exemplis” fits examples found in the tract at fol. 58v–59v, which were also not included in the later Theologia christiana.
Answering Objections and Confirming the Identification
The editor anticipates and refutes potential objections to his identification. The first objection is that the burned tract could not have survived. He refutes this by noting that the work had general approval and wide circulation through copying before its condemnation; it could easily escape destruction, especially if the burning was ordered by a papal command (such as Innocent II’s letter of 16 July 1141), and a copy could be hidden within a miscellany volume like the Erlangen codex. The second objection concerns Otto of Freising’s quoted words, “Sicut eadem oratio — spiritus sanctus,” which are absent from the tract. The editor argues this is not a weighty objection, since the passage may have stood in a lost part of book III, Otto may not be quoting verbatim, or he may be citing from an oral utterance, as indicated by the word dixit. The identification is further confirmed by showing that the tract was directed against Roscellin. From a letter of Roscellin discovered by Schmeller, we learn that Abelard had written to the church of St. Martin of Tours, where Roscellin was a canon. Abelard’s letter is lost, but Roscellin’s reply (Cousin, Bd. II, S. 792–803) shows that Abelard’s letter contained personal abuse and a refutation of Roscellin’s Trinitarian doctrine. The editor argues that this refutation either shared many points with the manuscript tract (since Abelard habitually repeated himself) or was the tract itself, given the direct addresses found within it.
The Testimony of the Prophets: David
The text of the tract itself then begins its argument, drawing on authorities. The author turns first to David, called the greatest of prophets and kings, citing his superior intelligence: “Super omnes docentes me intellexi, super senes intellexi.” David openly teaches the distinction of the Trinity in the verse “Verbo domini caeli firmati sunt, et spiritu oris eius omnis virtus eorum.” Elsewhere, David insinuates unity with trinity: “Benedicat nos deus, deus noster, benedicat nos deus, et metuant eum omnes fines terrae.” The threefold confession expresses the Trinity of persons: Father, Son, and Holy Spirit. The addition of “noster” designates the Son, showing he was given to us by the Father, since divine wisdom illuminated us through the incarnation of the Word, as the apostle says: “Proprio filio suo non pepercit deus, sed pro nobis omnibus tradidit illum.” The Psalmist opens the unity of divine substance by using “eum” (singular), not “eos” (plural), after the threefold naming. Isaiah’s vision of the Seraphim crying “Sanctus, sanctus, sanctus dominus deus Sabaoth” is consonant with this. The word “dominus” designates power, since lords rule; this power is also assigned to the name “deus,” because theos (Greek for god) means fear, per Isidore, and power is the fear of subjects.
The Word and the Spirit in Creation and Scripture
The author explains that the Word is called wisdom because a person’s intelligence is manifested chiefly through words. Moses, in the account of creation, writes “Dixit deus” and “et factum ita,” showing that God made all things in the Word, i.e., in his wisdom, rationally. The Psalmist says “Dixit et facta sunt,” meaning he created or ordered all things by reason. He also says “Qui fecit caelos in intellectu,” showing the Word is not audible or transitory but intelligible and permanent. Augustine describes divine locution as “ipsa dei dispositio non habens sonum strepentem et transeuntem, sed vim in perpetuo manentem.” In book eight on the Trinity, Augustine says the Son is called Word to show he existed from the Father. The name Holy Spirit expresses the affection of goodness and charity, since by the spirit of our mouth (breath) the mind’s affections are shown—sighing in love, groaning in sorrow or labor. Thus the Holy Spirit is put for good affection, per the book of Wisdom: “Benignus est spiritus sapientiae.” Here “spiritus sanctus” is proper to one person, though in another signification it is common to all three persons, since the divine substance is spiritual and holy. A common name is often transferred to one thing as proper; for example, “clerics” vs. “monks” (though monks are clerics), and “confessors” vs. “martyrs” (though martyrs are confessors). David teaches the eternal generation of the Son from the Father, introducing the Son’s person: “Dominus dixit ad me: filius meus es tu, ego hodie genui te.” “Hodie” is used for eternity (since in eternity all is present), and “genui” (past tense) for perfection—the Son is always being begotten and always has been begotten. David also says: “Permanebit cum sole et ante lunam in generationem et generationem,” and “Tecum principium in die virtutis tuae in splendoribus sanctorum, ex utero ante luciferum genui te.” Of the Spirit, it is said in Wisdom: “Est in illa Spiritus intellectus, spiritus unicus, multiplex, subtilis, mobilis,” and later “humanus, stabilis.” The Spirit is said to be from the same and diverse because he is the same in substance with the Father and Son, diverse in person.
Plato and the Philosophers as Witnesses
The author then introduces Plato, who is said to attribute all numerical consonance to the Spirit, teaching that universal concord rests in divine grace. The order of nature is traced by numerical proportions; arithmetic is called the mother and mistress of other arts. Plato’s statement that the soul of the world consists of indivisible and divisible substance, and of the same and diverse, can be understood as distinguishing the power of reason of the Spirit—deliberation about any thing considers whether it is simple or composite in itself, and same or diverse in comparison with others. Plato’s error in saying the world-soul was made (had a beginning) does not stray from truth, as will be shown later on the Spirit’s procession. Augustine (City of God, book 8) notes that some Christians marvel that Plato thought things congruent with our religion. Some thought Plato heard Jeremiah in Egypt or read prophetic scriptures, but chronology shows Plato was born about 100 years after Jeremiah prophesied; after Plato’s 81 years, about 60 years passed until Ptolemy had the scriptures translated by the seventy Hebrews. So Plato could not have seen Jeremiah or read the Greek translation. Augustine (Confessions, book 7) says he read in Platonic books (translated from Greek) that “In principio erat verbum, et verbum erat apud deum, et deus erat verbum,” and that all things were made through him, and that the Word was born of God—but not that the Word became flesh, nor that he died for the impious. The Sibyl is then introduced as a female witness, with Augustine’s authority.
The Second Book: Method and Purpose
The passage for the second book opens with a citation regarding Titus, son of Vespasian, who, after avenging the blood of the Lord by subverting Jerusalem, entered Rome as a victor. He was said to be of such goodness that, recalling at dinner he had done no good that day, he declared, “O friends, I have lost this day.” The author contrasts this with our own failure to perceive the loss of hours, days, and moments when we speak idle words, for which we must render a rational account on judgment day, unlike Titus who acted without the Gospel or apostolic doctrine. The second book begins by stating that the author has gathered testimonies of prophets and philosophers to establish the faith of the Holy Trinity. Since all controversy, as Cicero says, is in writing or reason, the author deemed it opportune to bring authorities from the writings of excellent wise men and to support them with reasons where they seem irrationally attacked, lest the verbosity of Christ’s enemies insult our simplicity. Many now cry out as heralds of the great Antichrist, through whom the enemy of the human race tries to undermine faith, the foundation of all good. Miracles have passed, malice has grown; since we cannot fight with deeds, we must fight with words, trusting in the truth that says, “I will give you a mouth and wisdom.”
Against Pseudo-Dialecticians and the Limits of Reason
Against pseudo-dialecticians, the author notes that professors of dialectic and the importunity of sophists, whom Plato ridicules as blessed by a flood of words, seek the faith of the Trinity more subtly. The author condemns not the science of dialectic but the fallacy of sophistry, citing Augustine’s praise of dialectic in De ordine and De doctrina christiana, where it is said to be most necessary for penetrating questions in sacred letters, though the lust of quarreling must be avoided. The Peripatetics, now called dialecticians, repressed heresies of Stoics and Epicureans with right reasons, such as arguing against the Stoics on free will, as Aristotle says in Periermenias. No science is evil, even knowledge of evil, for knowing sin is not sinning; God knows all things. The power of evil is also good, necessary for merit, as the prophet says, “Who could transgress and did not.” The author cites Pilate’s power given from above. The familiar vice of science is pride, per “Knowledge puffs up”; pride expelled the first angel and makes heretics, who desire novelty. The author quotes Plato’s Timaeus: finding the maker of the universe is difficult, and declaring him is impossible. Plato did not presume to explain the generation of the Word. Hermes said the Son’s name cannot be told by human mouth. Dionysius the Areopagite showed the altar of the unknown god to the apostle Paul. Faith should be believed even if it cannot be explained, for, as Gregory says, faith has no merit where human reason provides proof. Ambrose wrote to Emperor Gratian that the secret of generation is impossible to know, above powers, angels, Cherubim, and Seraphim. The author will answer fools according to their folly, using the sword of dialectic against them, as David slew Goliath with his own sword. The author promises not to teach the truth, which no mortal knows, but something verisimilar and near human reason, not contrary to sacred scripture. The plan is to state the theme of the unity of divine substance and trinity of persons, then objections, then solutions.
The Singular Substance and Personal Distinction
The argument proceeds by clarifying that each of the three persons is fully God and Lord, yet there are not three gods or lords, because the three share one utterly singular and individual essence. There is no substantial difference between them: the Father is not substantially other than the Son or the Holy Spirit, nor is the Son substantially other than the Spirit. They are alius—another person—but not aliud—another thing—in nature. The distinction is personal, not natural. The Father is personally discrete from the Son and the Spirit, so that the Father is not the Son nor the Spirit, even though each is the same divine substance. The analogy of Socrates and Plato is invoked: Socrates is personally other than Plato, discrete in his own essence, yet not substantially different, since both share the same specific nature of humanity. Much less can any of the three divine persons be called aliud from another, since their substance is utterly singular, admitting no diversity of parts or forms.
Augustine on Divine Simplicity
Augustine is quoted from De civitate Dei XI to explain why God is called simple. God is not simple because the Father alone, or the Son alone, or the Spirit alone is in that nature, nor because the Trinity is a mere name without subsistence, as the Sabellians thought. Rather, God is simple because each person is what it has, except for relative terms spoken of one person toward another. The Father has a Son but is not the Son; the Son has a Father but is not the Father. Whatever is said of a person toward itself, that person is—for instance, living, the person is that life. Unlike a vessel containing liquid, or a body having color, or air having light, God cannot be deprived of what he has. Augustine is also quoted from the Confessiones VII: God’s will is not greater than his power, and God’s will and power are God himself.
Against Accidents and Forms in God
The divine substance is free from all accidents and all participation in form: nothing is in God that God is not. Everything that subsists is either eternal, which is God, or began from the supreme principle. If God’s power or wisdom were something in God that God is not, it would have begun; then God would have existed without them—not always powerful or wise—and would have created them while lacking wisdom, making some works irrational. If qualities in God are said to be coeternal with the divine substance, one must ask whether they are substantial or accidental. If substantial, they are naturally prior to God, as rationality is prior to a human. If accidental, they are posterior; but Porphyry says an accident can be absent without corruption of the subject. Thus God could exist without wisdom or power, which even a heretic would abhor.
The Singular, Uniform Divine Substance
The divine substance remains wholly individual and uniform, hence it is rightly called perfect good, needing nothing, having from itself, receiving from no other. Creatures, however good, need something else, showing their imperfection. Virtues need a subject; the soul needs virtues to be good. Since the three persons share one singular essence—the Father’s essence is entirely the Son’s and the Spirit’s—yet the Father is personally diverse from the Son and Spirit, a subtle discernment is needed: neither does the identity of substance hinder personal diversity, nor does personal diversity hinder substantial singularity. God is simultaneously one in substance and three in persons.
Objections Against the Trinity
Fifteen objections are listed against this doctrine. First, if diversity is only in words, the Trinity is not eternal, since names were imposed by humans. Second, if distinction follows the number of names, there would be many more than three persons, such as deus, dominus, aeternus, and so on. Third, if diversity is in the thing, and nothing is in God but the singular substance, God would be trinus in substance. Fourth, if substance and persons are identical, then unity in substance implies unity in persons, and trinity in persons implies trinity in substance. Fifth, how can there be three persons where there are not three things, nor multitude—and multitude cannot arise from one thing without parts? Sixth, how can Father and Son be “such as” each other without similarity, which requires discrete things? Seventh, everything that exists is either substance or form; how can there be many without these? Eighth, since “deus” names substance, not person, why say “trinus deus” rather than “trina substantia”? Ninth, “trinus deus” sounds like “three gods,” just as “trina oratio” means three prayers. Tenth, how can three be discrete yet not be multiple substances, since “plures substantiae” means multiple things each of which is a substance? Eleventh, why say “three persons” rather than “three gods,” since each is both? Twelfth, if no difference in being substance or God prevents saying “three gods,” then by the same reasoning we could never say “several humans” or “several persons.” Thirteenth, “three persons are” implies “three beings/essences,” since the participle follows the verb’s number, per Aristotle: “to walk” equals “to be walking.” Fourteenth, how is “deus” singular, not universal, if three numerically distinct things are each God? Fifteenth, no difference can exist where the essence is one and individual; all difference is either between discrete essences or in one thing through variation—but God has no variation, as it is written, “Apud quem non est transmutatio.”
God’s Exclusion from Peripatetic Categories
Substances are called “subsistences” and are naturally prior to other things that assist them but do not subsist through themselves. From this it is clear that God—the unique and singular principle of all things—cannot in any way be contained in the true number of things that are not substances. Nor, according to the Peripatetics, is God placed under substance, although He alone is the thing existing through Himself, having true and immutable being from Himself, from whom all things come. This can easily be shown from the writings of all dialecticians, namely Porphyry, Aristotle, and Boethius. Porphyry says in his Isagoge that each substance participates in one species, but in many accidents, both separable and inseparable. Aristotle in the Categories assigns the proper property of substance: “Most properly, it seems to be proper to substance that, being one and the same in number, it is receptive of contraries.” Since these cannot apply to God—whose substance can neither be varied by accidents nor subjected to any forms—it is clear the philosophers did not receive Him among substances, just as Plato placed matter between no substance and some substance, conceiving it as entirely formless. God is not substance if we attend to the nature of true subsistence and immutable being in Him; nor is He substance if we follow the usual meaning of the name, since He cannot be subjected to accidents. Boethius proves in the second book of the Topics that whiteness is not substance: “Substance is what can be subject to all accidents; whiteness is subject to no accidents; therefore whiteness is not substance.” Thus the supreme majesty is entirely excluded from Peripatetic treatment; their rules do not ascend to that ineffable height, but are content with created natures.
On Language and Time
All human speech is accommodated to creatures, as shown by the verb, which signifies time that began with the world. When we say God is prior to the world or existed before times, no true sense of precedence or succession can be understood if we take these words according to human institution and temporal signification. Words transferred to the singular divine nature contract a singular signification and exceed their proper institution. Gregory in the prologue to the Moralia says: “I deem it utterly unworthy to restrict the words of the heavenly oracle under the rules of Donatus.”
Against the Pseudodialecticians
The author addresses an “astute dialectician” who argues from Peripatetic authority. Each science uses its own words; the tractators of that singular highest good ought to have singular words. Since man could not understand God, he dared not name Him; all words said of God are translations and parabolic enigmas. The author will use human reasons to refute the pseudodialecticians, citing Proverbs: “Answer the fool according to his folly.”
On the Same and Diverse
“Same” is said in six or more modes: according to essence, as sword and blade; by definition, as ensis and mucro, where each follows from the other; by similitude, as individuals in a species; as unchanged, as God is always the same; by effect or value. “Diverse” is said in corresponding modes: essentially, numerically, by definition. Things numerically diverse are those wholly discrete in their entire essence, as Socrates and Plato.
Sophisms About Predication
The text continues the logical analysis of terms applied to God, addressing sophisms about predication. It argues that if something is “twenty-one” or “twenty,” it does not follow that it is “one”; a half or imperfect house is not thereby a house; a “laughing meadow” is not thereby laughing; a “great thief” is not thereby great; being “good according to opinion” does not make one good; the Word being “made flesh” does not mean it is “made” simply; God being “made a helper” does not mean He is made; a “simple proposition” is not simple in the sense of having no parts at all; dispersed things forming “one multitude” are not thereby one; and the soul being “many persons” or “many places” according to dialecticians does not make it many, that is, many mutually discrete things. The soul is “many persons” grammatically—when someone speaks to it or about it, or when diverse arguments can be made from it, or by opposition, similarity, or other relations—yet it is not simply “many.” Likewise, God is “many persons” (Father, Son, Holy Spirit), but not “many things” or “many essences,” since the same essence that is the Father is also the Son and the Holy Spirit.
The Meaning of “Three” and “Many”
The names “many,” “three,” and other numerals pertain properly to number and should be taken only for things diverse in number. God could be called “three” or “many” if we understand this by definition rather than number—He is eternal, immense, creator, omnipotent, and many other things diverse by definitions, so a certain multitude of properties, not number, can be noted. The Apostle says: “And there are three who give testimony in heaven, and the three are one,” adding nothing to the word “three.” Augustine in On the Trinity, book 7, confirms this, fearing to say “three essences” lest diversity be understood in the highest equality, yet unable to say “not three,” as Sabellius said.
The Trinity as Whole and Parts
If the multitude of persons is said to be a multitude, then it would have parts. But a part, according to Boethius, is prior to that of which it is a part, and the division of a whole into parts is into prior things, as genus into species. Thus each of the three persons would be prior to the trinity they constitute, if not in time, at least in nature—like rationality is prior to rational animal. But one recoils from anything prior or posterior in the deity. The response is that philosophical authority takes “part” in quantity, which is not in God, whose substance is entirely simple. Boethius, in saying the part’s essence is not the whole’s essence, shows he means a part essentially diverse from its whole—impossible in the trinity, where the essence of the whole trinity and of each person is one and the same. Therefore, neither is the trinity a whole, nor is anything in God prior or posterior, especially regarding eternity and necessity, since the trinity and each person are eternal and necessary. What is eternal and necessary has nothing naturally prior to it, for what is led to being becomes what it is not yet; per Aristotle, what is made is not yet what it becomes; if it begins, it is not eternal, since the eternal, per Boethius, lacks origin. The trinity takes no origin from the persons, though it consists in them—”in” three persons rather than “from” three, since “from” suggests a material principle, while “in” shows the trinity consists in them, so that “trinity” sounds identically to “three persons.”
Simultaneity of Persons and Trinity
Even in creatures, a multitude can be simultaneous with its parts, as with relatives: the multitude of lord and servant is simultaneous with each, since a lord cannot exist without a servant. Likewise, this finger and the multitude of two fingers are diverse by essence, yet the part-multitude cannot be prior to the whole-multitude, since it cannot exist without the other finger. Thus each person is not prior to the trinity but naturally simultaneous with it, since no person can exist without the others, and all are eternal and necessary.
On Posterior Attributes and Variation
Things not pertaining to eternity—like God being creator, lord, ruler, merciful, judge, or incarnate—can be called posterior to God, as this body is prior to this man, the same substance being first a body, then a man. So God was not eternally lord or creator, if “always” means eternally, not temporally, per Genesis: “Let there be lights… for signs and seasons.” To the objection of variation, the reply is that as the Holy Spirit is called multiple by effects, not in Himself, so God varies in effects but remains immutable in Himself, nothing in the divine substance being at one time that it was not before.
On “Such as the Father, Such the Son”
On “such as the Father, such the Son”: this implies similarity, meaning “not diverse in any good of majesty”—a negation rather than affirmation. “Equal” means “in no way less in divinity,” being of the same essence. Athanasius, adding “Immense Father, immense Son,” shows how to understand this. Things can be called similar not only when essentially diverse but also when disjoined by properties, as proposition and conclusion agree in terms. “Similar” can also mean “the same,” as Boethius says in the Topics: a place from the contrary and from repugnants is “consimilar,” that is, identical; so the Father is similar to the Son as the same in substance. The objection that everything existing is substance or form is answered by the preceding arguments, which have shown that the divine simplicity transcends such categories, and that the highest unity of the three persons is a mystery of faith, not a contradiction of reason, so that the book concludes by affirming that God is one in substance and three in persons, and that this truth, though ineffable, is to be held firmly against all heretical distortions.
Main Arguments
The central argument of the treatise is that the doctrine of the Trinity—one God in three persons—is both rationally defensible and consistent with the authorities of scripture, the Church Fathers, and even pagan philosophy. Abelard seeks to show that the unity of divine substance and the trinity of persons do not contradict each other, and that apparent logical difficulties can be resolved through careful attention to the modes of signification and predication.
The first major argument concerns the relationship between the three persons and the divine substance. Abelard argues that each of the three persons is God and Lord, yet there are not multiple gods or lords, because the three persons share one utterly individual and singular essence or substance. The persons have no substantial difference from one another: the Father is not substantially other than the Son or the Holy Spirit, nor the Son than the Holy Spirit. They are alius (another person) but not aliud (another thing) in nature. The distinction is personal, not natural: the Father is personally discrete from the Son and Spirit, so that the Father is not the Son nor the Spirit, even though each is the same divine substance. The analogy of Socrates and Plato is used: Socrates is personally other than Plato, discrete in his own essence, yet not substantially different, since both share the same specific nature of humanity. Much less can any of the three divine persons be called aliud from another, since their substance is utterly singular, admitting no diversity of parts or forms.
A second major argument concerns divine simplicity. Drawing on Augustine, Abelard argues that God is called simple not because the Father alone or Son alone or Spirit alone is in that nature, nor because the Trinity is a mere name without subsistence (as the Sabellians thought), but because each person is what it has—except for relative terms spoken of one person toward another. The Father has a Son but is not the Son; the Son has a Father but is not the Father. Whatever is said of a person toward itself, that person is—e.g., living, the person is that life. Unlike a vessel containing liquid, or body having color, or air having light, God cannot be deprived of what he has. The divine substance is free from all accidents and all participation in form: nothing is in God that God is not. If God’s power or wisdom were something in God that God is not, it would have begun; then God would have existed without them—not always powerful or wise—and would have created them while lacking wisdom, making some works irrational. If qualities in God are said to be coeternal with the divine substance, one must ask whether they are substantial or accidental. If substantial, they are naturally prior to God (as rationality is prior to a human). If accidental, they are posterior; but an accident can be absent without corruption of the subject. Thus God could exist without wisdom or power—which even a heretic would abhor.
A third argument concerns the exclusion of God from the Peripatetic categories. Abelard argues that God cannot in any way be contained in the true number of things that are not substances, nor is God placed under substance according to the Peripatetics, although He alone is the thing existing through Himself, having true and immutable being from Himself, from whom all things come. This is shown from the writings of Porphyry, Aristotle, and Boethius. Porphyry says that each substance participates in one species, but in many accidents. Aristotle assigns the proper property of substance: “Most properly, it seems to be proper to substance that, being one and the same in number, it is receptive of contraries.” Since these cannot apply to God—whose substance can neither be varied by accidents nor subjected to any forms—it is clear the philosophers did not receive Him among substances. Boethius proves that whiteness is not substance because substance is what can be subject to all accidents, while whiteness is subject to no accidents. Thus the supreme majesty is entirely excluded from Peripatetic treatment; their rules do not ascend to that ineffable height, but are content with created natures.
A fourth argument concerns the proper understanding of language about God. All human speech is accommodated to creatures, as shown by the verb, which signifies time that began with the world. When we say God is prior to the world or existed before times, no true sense of precedence or succession can be understood if we take these words according to human institution and temporal signification. Words transferred to the singular divine nature contract a singular signification and exceed their proper institution. Gregory in the prologue to the Moralia says: “I deem it utterly unworthy to restrict the words of the heavenly oracle under the rules of Donatus.” Since man could not understand God, he dared not name Him; all words said of God are translations and parabolic enigmas.
A fifth argument concerns the resolution of the fifteen objections against the Trinity. Abelard addresses each objection through careful logical analysis. For example, to the objection that if diversity is only in words, the Trinity is not eternal since names were imposed by humans, he argues that the distinction of persons is not merely verbal but real, though not substantial. To the objection that if distinction follows the number of names, there would be many more than three persons, he argues that the names “deus,” “dominus,” “aeternus,” etc., do not name persons but properties or attributes. To the objection that if substance and persons are identical, then unity in substance implies unity in persons, he argues that the identity is not simple but qualified: the persons are identical in substance but distinct in personhood. The discussion of the modes of “same” and “diverse” is central to this resolution: “same” is said in six or more modes—according to essence (as sword and blade), by definition (as ensis and mucro), by similitude (as individuals in a species), as unchanged (as God is always the same), by effect or value. “Diverse” is said in corresponding modes: essentially, numerically, by definition. Things numerically diverse are those wholly discrete in their entire essence, as Socrates and Plato.
A sixth argument concerns the proper understanding of terms like “three” and “many” as applied to God. Abelard argues that the names “many,” “three,” and other numerals pertain properly to number and should be taken only for things diverse in number. God could be called “three” or “many” if we understand this by definition rather than number—He is eternal, immense, creator, omnipotent, and many other things diverse by definitions, so a certain multitude of properties (not number) can be noted. The Apostle says: “And there are three who give testimony in heaven, and the three are one,” adding nothing to the word “three.” Augustine confirms this, fearing to say “three essences” lest diversity be understood in the highest equality, yet unable to say “not three,” as Sabellius said.
Key Concepts
Several specific concepts and distinctions are central to the treatise’s argument and recur throughout its three books.
The distinction between alius and aliud is fundamental. The three divine persons are alius (another person) but not aliud (another thing) in nature. The Father is personally discrete from the Son and Spirit, so that the Father is not the Son nor the Spirit, even though each is the same divine substance. This distinction allows Abelard to affirm both the real distinction of persons and the numerical identity of substance.
The concept of divine simplicity is developed through the principle that each person is what it has, except for relative terms spoken of one person toward another. The Father has a Son but is not the Son; the Son has a Father but is not the Father. Whatever is said of a person toward itself, that person is—e.g., living, the person is that life. This principle rules out any composition in God, whether of substance and accidents, or of form and matter.
The exclusion of God from the Peripatetic categories is a key negative thesis. God is not substance in the Aristotelian sense, since substance is receptive of contraries and subject to accidents, neither of which applies to God. The divine substance is free from all accidents and all participation in form: nothing is in God that God is not. The rules of the categories are content with created natures and do not ascend to the divine height.
The modes of “same” and “diverse” provide the logical framework for understanding Trinitarian predication. “Same” is said in six or more modes: according to essence (as sword and blade), by definition (as ensis and mucro), by similitude (as individuals in a species), as unchanged (as God is always the same), by effect or value. “Diverse” is said in corresponding modes: essentially, numerically, by definition. Things numerically diverse are those wholly discrete in their entire essence, as Socrates and Plato. This framework allows Abelard to say that the Father and Son are the same in substance but diverse in person.
The concept of the world-soul in Plato’s Timaeus is interpreted as an anticipation of the Holy Spirit. Plato is said to attribute all numerical consonance to the Spirit, teaching that universal concord rests in divine grace. The order of nature is traced by numerical proportions; arithmetic is called the mother and mistress of other arts. Plato’s statement that the soul of the world consists of indivisible and divisible substance, and of the same and diverse, is understood as distinguishing the power of reason of the Spirit—deliberation about any thing considers whether it is simple or composite in itself, and same or diverse in comparison with others. Plato’s error in saying the world-soul was made does not stray from truth, as will be shown later on the Spirit’s procession.
The distinction between the Holy Spirit as proper to one person and as common to all three is important. The name Holy Spirit expresses the affection of goodness and charity, since by the spirit of our mouth (breath) the mind’s affections are shown—sighing in love, groaning in sorrow or labor. Thus the Holy Spirit is put for good affection. Here “spiritus sanctus” is proper to one person, though in another signification it is common to all three persons, since the divine substance is spiritual and holy. A common name is often transferred to one thing as proper; e.g., “clerics” vs. “monks” (though monks are clerics), and “confessors” vs. “martyrs” (though martyrs are confessors).
The concept of the Word as wisdom is developed through the claim that a person’s intelligence is manifested chiefly through words. Moses, in creation, writes “Dixit deus” and “et factum ita,” showing God made all things in the Word, i.e., in his wisdom, rationally. The Psalmist says “Dixit et facta sunt,” meaning he created or ordered all things by reason. He also says “Qui fecit caelos in intellectu,” showing the Word is not audible or transitory but intelligible and permanent. Augustine describes divine locution as “ipsa dei dispositio non habens sonum strepentem et transeuntem, sed vim in perpetuo manentem.”
The concept of the eternal generation of the Son is taught through the Psalmist’s words: “Dominus dixit ad me: filius meus es tu, ego hodie genui te.” “Hodie” is used for eternity (since in eternity all is present), and “genui” (past tense) for perfection—the Son is always being begotten and always has been begotten. This paradoxical formulation captures the eternal, non-temporal nature of the Son’s generation from the Father.
The concept of the trinity as consisting “in” three persons rather than “from” three is a subtle distinction. “From” suggests a material principle, while “in” shows the trinity consists in them, so that “trinity” sounds identically to “three persons.” This avoids the implication that the persons are prior to the trinity or that the trinity is composed of pre-existing parts.
The concept of the divine names as translations and parabolic enigmas is central to the treatise’s approach to theological language. Since man could not understand God, he dared not name Him; all words said of God are translations and parabolic enigmas. This does not mean that language about God is meaningless, but that it must be understood as accommodated to creatures and exceeding its proper institution when transferred to the divine nature.
Themes
The treatise develops several deeper themes that give it significance beyond its immediate argumentative purpose.
The relationship between faith and reason is a pervasive theme. Abelard insists that faith should be believed even if it cannot be explained, citing Gregory: “faith has no merit where human reason provides proof.” Yet he also insists on the legitimacy and necessity of rational inquiry into the faith, using the sword of dialectic against those who would undermine the faith with sophistry. He promises not to teach the truth, which no mortal knows, but something verisimilar and near human reason, not contrary to sacred scripture. This tension—between the ineffability of God and the obligation to give a rational account of the faith—runs throughout the treatise. The author will answer fools according to their folly, using the sword of dialectic against them, as David slew Goliath with his own sword.
The theme of the insufficiency of human language to speak of God is closely related. All human speech is accommodated to creatures, and words transferred to the singular divine nature contract a singular signification and exceed their proper institution. The author cites Gregory: “
