Letter of Thomas Jefferson to John Adams (July 5, 1814). Reprinted in Bernard Mayo, Jefferson Himself, “The whimsies and jargon of Plato,” University Press of Virginia, 1942, pp. 300-301.

I am just returned from one of my long absences, having been at my other home for five weeks past. Having more leisure there than here for reading, I amused myself with reading seriously Plato’s Republic. I am wrong, however, in calling it amusement, for it was the heaviest task-work I ever went through. I had occasionally before taken up some of his other works, but scarcely ever had patience to go through a whole dialogue. While wading through the whimsies, the puerilities, and unintelligible jargon of this work, I laid it down often to ask myself how it could have been that the world should have so long consented to give reputation to such nonsense as this….
In truth, he is one of the race of genuine sophists, who has escaped the oblivion of his brethren, first by the elegance of his diction, but chiefly by the adoption and incorporation of his whimsies into the body of artificial Christianity. His foggy mind is forever presenting the semblances of objects which, half seen through a mist, can be defined neither in form nor dimensions. Yet this, which should have consigned him to early oblivion, really procured him immortality of fame and reverence. The Christian priesthood, finding the doctrines of Christ leveled to every understanding, and too plain to need explanation, saw in the mysticism of Plato materials with which they might build up an artificial system which might, from its indistinctness, admit everlasting controversy, give employment for their order, and introduce it to profit, power, and pre-eminence. The doctrines which flowed from the lips of Jesus himself are within the comprehension of a child; but thousands of volumes have not yet explained the Platonisms engrafted on them; and for this obvious reason, that nonsense can never be explained.