4.

I perceive that all those images which you as well as many others call phantasiae, may be most conveniently and accurately divided into three classes, according as they originate with the senses, or the imagination, or the faculty of reason. Examples of the first class are when the mind forms within itself and presents to me the image of your face, or of Carthage, or of our departed friend Verecundus, or of any other thing at present or formerly existing, which I have myself seen and perceived. Under the second class come all things which we imagine to have been, or to be so and so: e.g. when, for the sake of illustration in discourse, we ourselves suppose things which have no existence, but which are not prejudicial to truth; or when we call up to our own minds a lively conception of the things described while we read history, or hear, or compose, or refuse to believe fabulous narrations. Thus, according to my own fancy, and as it may occur to my own mind, I picture to myself the appearance of Aeneas, or of Medea with her team of winged dragons, or of Chremes, or Parmeno. ¹ To this class belong also those things which have been brought forward as true, either by wise men wrapping up some truth in the folds of such inventions, or by foolish men building up various kinds of superstition; e.g. the Phlegethon of Tortures, and the five caves of the nation of darkness, ² and the North Pole supporting the heavens, and a thousand other prodigies of poets and of heretics. Moreover, we often say, when carrying on a discussion, "Suppose that three worlds, such as the one which we inhabit, were placed one above another;" or, "Suppose the earth to be enclosed within a four-sided figure," and so on: for all such things we picture to ourselves, and imagine according to the mood and direction of our thoughts. As for the third class of images, it has to do chiefly with numbers and measure; which are found partly in the nature of things, as when the figure of the entire world is discovered, and an image consequent upon this discovery is formed in the mind of one thinking upon it; and partly in sciences, as in geometrical figures and musical harmonies, and in the infinite variety of numerals: which, although they are, as I think, true in themselves as objects of the understanding, are nevertheless the causes of illusive exercises of the imagination, the misleading tendency of which reason itself can only with difficulty withstand; although it is not easy to preserve even the science of reasoning free from this evil, since in our logical divisions and conclusions we form to ourselves, so to speak, calculi or counters to facilitate the process of reasoning.