Ocellus adds, “that it is his intention [in this treatise On the Universe] to derive what is _probable_ from intellectual perception.” For in physiological discussions we must be satisfied with probability and an approximation to the truth. Hence, Proclus, in his Commentary on that part of the Timæus in which Plato says, “What essence is to generation, that truth is to faith,” admirably observes as follows: “The faith of which Plato now speaks is rational, but is mingled with irrational knowledge, as it employs sense and conjecture; hence, it is filled with much of the unstable. For receiving from sense or conjecture the ὁτι, _or that a thing is_, it thus explains causes. But these kinds of knowledge have much of the confused and unstable. Hence, Socrates, in the Phædo, reprehends sense in many respects, because we neither hear nor see anything accurately. “How, therefore, can the knowledge which originates from sense possess the accurate and the irreprehensible? For the powers which use science alone, comprehend the whole of the thing known with accuracy; but those that energise with sense, are deceived, and deviate from accuracy, on account of sense, and because the object of knowledge is unstable. For, with respect to that which is material, what can any one say of it? since it is always changing and flowing, and is not naturally adapted to abide for a moment. But that which is celestial, in consequence of being remote from us, is not easily known, nor can it be apprehended by science, but we must be satisfied in the theory of it with an approximation to the truth, and with probability [instead of certainty]. For everything which is in place requires the being situated there, in order to a perfect knowledge of its nature. The intelligible, however, is not a thing of this kind, since it is not apprehended by us in place; for, wherever any one establishes his reasoning energy, there, truth being everywhere present, he comes into contact with it. But if it is possible to assert anything firm and stable about that which is celestial, this also is possible, so far as it participates of being, and so far as it can be apprehended by intelligence. For, if anything necessary can be collected concerning it, it is alone through geometrical demonstrations which are universal. But so far as it is sensible, it is difficult to be apprehended, and difficult to be surveyed.”—See the first volume of my translation of Proclus on the Timæus of Plato, p. 291.