Here is the passage in the XXIst chapter of The Decline and Fall of the Roman Empire in which Gibbon discusses Plato’s philosphy and provides an account of how Plato, grappling with the problem of “how a Being purely incorporeal could… mould with a plastic hand the rude and independent chaos”, responded to the problem by developing a trinitarian divinity:
The genius of Plato, informed by his own meditation, or by the traditional knowledge of the priests of Egypt, had ventured to explore the mysterious nature of the Deity. When he had elevated his mind to the sublime contemplation of the first self−existent, necessary cause of the universe, the Athenian sage was incapable of conceiving how the simple unity of his essence could admit the infinite variety of distinct and successive ideas which compose the model of the intellectual world; how a Being purely incorporeal could execute that perfect model, and mould with a plastic hand the rude and independent chaos. The vain hope of extricating himself from these difficulties, which must ever oppress the feeble powers of the human mind, might induce Plato to consider the divine nature under the threefold modification − of the first cause, the reason, or Logos, and the soul or spirit of the universe. His poetical imagination sometimes fixed and animated these metaphysical abstractions; the three archical on original principles were represented in the Platonic system as three Gods, united with each other by a mysterious and ineffable generation; and the Logos was particularly considered under the more accessible character of the Son of an Eternal Father, and the Creator and Governor of the world.
However, in a lengthy footnote, Gibbon dismisses the view that Plato’s doctrine was trinitarian:
This exposition of the doctrine of Plato appears to me contrary to the true sense of that philosopher’s writings. The brilliant imagination which he carried into metaphysical inquiries, his style, full of allegories and figures, have misled those interpreters who did not seek, from the whole tenor of his works and beyond the images which the writer employs, the system of this philosopher. In my opinion, there is no Trinity in Plato; he has established no mysterious generation between the three pretended principles which he is made to distinguish. Finally, he conceives only as attributes of the Deity, or of matter, those ideas, of which it is supposed that he made substances, real beings.
According to Plato, God and matter existed from all eternity. Before the creation of the world, matter had in itself a principle of motion, but without end or laws: it is this principle which Plato calls the irrational soul of the world, because, according to his doctrine, every spontaneous and original principle of motion is called soul. God wished to impress form upon matter, that is to say, 1. To mould matter, and make it into a body; 2.To regulate its motion, and subject it to some end and to certain laws. The Deity, in this operation, could not act but according to the ideas existing in his intelligence: their union filled this, and formed the ideal type of the world. It is this ideal world, this divine intelligence, existing with God from all eternity, and called by Plato which he is supposed to personify, to substantialize; while an attentive examination is sufficient to convince us that he has never assigned it an existence external to the Deity, (hors de la Divinite,) and that he considered the Aoyot as the aggregate of the ideas of God, the divine understanding in its relation to the world. The contrary opinion is irreconcilable with all his philosophy: thus he says that to the idea of the Deity is essentially united that of intelligence, of a logos. He would thus have admitted a double logos; one inherent in the Deity as an attribute, the other independently existing as a substance. He affirms that the intelligence, the principle of order cannot exist but as an attribute of a soul, the principle of motion and of life, of which the nature is unknown to us. How, then, according to this, could he consider the logos as a substance endowed with an independent existence? In other places, he explains it by these two words, knowledge, science, which signify the attributes of the Deity. When Plato separates God, the ideal archetype of the world and matter, it is to explain how, according to his system, God has proceeded, at the creation, to unite the principle of order which he had within himself, his proper intelligence, the principle of motion, to the principle of motion, the irrational soul which was in matter. When he speaks of the place occupied by the ideal world, it is to designate the divine intelligence, which is its cause. Finally, in no part of his writings do we find a true personification of the pretended beings of which he is said to have formed a trinity: and if this personification existed, it would equally apply to many other notions, of which might be formed many different trinities.
This error, into which many ancient as well as modern interpreters of Plato have fallen, was very natural. Besides the snares which were concealed in his figurative style; besides the necessity of comprehending as a whole the system of his ideas, and not to explain isolated passages, the nature of his doctrine itself would conduce to this error. When Plato appeared, the uncertainty of human knowledge, and the continual illusions of the senses, were acknowledged, and had given rise to a general scepticism. Socrates had aimed at raising morality above the influence of this scepticism: Plato endeavored to save metaphysics, by seeking in the human intellect a source of certainty which the senses could not furnish. He invented the system of innate ideas, of which the aggregate formed, according to him, the ideal world, and affirmed that these ideas were real attributes, not only attached to our conceptions of objects, but to the nature of the objects themselves; a nature of which from them we might obtain a knowledge. He gave, then, to these ideas a positive existence as attributes; his commentators could easily give them a real existence as substances; especially as the terms which he used to designate them, essential beauty, essential goodness, lent themselves to this substantialization, (hypostasis.) − G.
In a footnote a little further on, Gibbon cites the “modern writers” who have influenced his opinion:
The modern guides who lead me to the knowledge of the Platonic system are Cudworth, Basnage, Le Clerc, and Brucker. As the learning of these writers was equal, and their intention different, an inquisitive observer may derive instruction from their disputes, and certainty from their agreement.
While searching for more information on the subject I came across a book written just a couple of decades after the publication of Gibbon’s history by one Caesar Morgan, chaplain to the Lord Bishop of Ely. The book is grandly titled, “An Investigation of the Trinity of Plato and of Philo Judaeus, and of the Effects Which an Attachment to Their Writings Had Upon the Principles and Reasonings of the Fathers of the Christian Church.”
I was expecting Morgan to offer a defence of the view that Plato’s philosophy has a trinitarian character to it, but in fact it was Ralph Cudworth, one of the Cambridge Platonists, who maintained that view, a view which Morgan came to reject after looking into the matter.
Actually, the doctrine of the trinity of Plato was widely held in the 17th and 18th centuries, no doubt due in large part to the influence of Cudworth. It was an opinion that Caesar Morgan had assumed to be true, simply because it was so widely held, as he explains:
The course of my own reading had led me to adopt the commonly received opinion, that Plato had some knowledge of the profound and mystical doctrine of the Trinity. I was the less inclined to question the truth of this opinion, as it was almost the only one in which the controversialists of the present day were generally agreed. When, therefore, I was excited to enter into a minute examination of this subject, my original object was not to ascertain the truth of the opinion, that Plato was acquainted with the doctrine of the Trinity of persons in the divine nature. Of this I entertained no doubt. But I wished to know by what authority, or by what train of reasoning, he was led to embrace this doctrine ; by what arguments he supported it ; and in what sense he explained it. So far was I from entertaining prejudices in favour of the side of the question, which I have since found reason to maintain, that I did not even suspect the possibility of its being true, at the time when I instituted the inquiry.
Caesar Morgan concludes that,
Most of the defenders and opposers of this doctrine in modern times agree in maintaining that the doctrine of the Trinity is delivered and inculcated in the writings of Plato. Hence the orthodox conclude, that, though this great mystery is more fully set forth in the Holy Scriptures, and derives its chief authority from divine revelation; yet, either the doctrine itself is congenial to the mind of man, and regularly deducible from principles of reason ; or, that it was handed down in the heathen world by uninterrupted tradition from remote antiquity. The opposers of our faith, on the contrary, infer from the same premises, that the doctrine itself is no part of genuine Christianity : that it is the natural production of philosophy, falsely so called : and that it was introduced into the Church of Christ by men, who with their subtleties distorted the graceful form, and corrupted the simplicity of our holy religion.
In the course of the preceding enquiry, I have found myself obliged to differ in some points from both those parties. After a minute and impartial examination of the writings of Plato, I cannot find anything which sufficiently proves him to have had even an obscure knowledge of the mysterious doctrine of the Trinity.
In reaching that conclusion he, an Anglican divine, is in complete agreement with Gibbon, an Enlightenment sceptic.
- Edward Gibbon: The Decline And Fall Of The Roman Empire vol II
- Caesar Morgan: An Investigation Into The Trinity Of Plato And Philo
- Plato: Philebus
- Stanford Encylopedia Of Philosophy: The Cambridge Platonists
- Encyclopedia Britannica, VI ed: Plato and Cudworth