From Plato's seventh letter to ; Liebes, v. 5. For everything that exists there are three instruments by which the knowledge of it is necessarily imparted; fourth, there is the knowledge itself, and, as fifth, we must count the thing itself which is known and truly exists. The first is the name, the, second the definition, the third. the image, and the fourth the knowledge. If you wish to learn what I mean, take these in the case of one instance, and so understand them in the case of all. A circle is a thing spoken of, and its name is that very word which we have just uttered. The second thing belonging to it is its definition, made up names and verbal forms. For that which has the name "round," "annular," or, "circle," might be defined as that which has the distance from its circumference to its centre everywhere equal. Third, comes that which is drawn and rubbed out again, or turned on a lathe and broken up-none of which things can happen to the circle itself-to which the other things, mentioned have reference; for it is something of a different order from them. Fourth, comes knowledge, intelligence and right opinion about these things. Under this one head we must group everything which has its existence, not in words nor in bodily shapes, but in souls-from which it is dear that it is something different from the nature of the circle itself and from the three things mentioned before. Of these things intelligence comes closest in kinship and likeness to the fifth, and the others are farther distant. The same applies to straight as well as to circular form, to colours, to the good, the, beautiful, the just, to all bodies whether manufactured or coming into being in the course of nature, to fire, water, and all such things, to every living being, to character in souls, and to all things done and suffered. For in the case of all these, no one, if he has not some how or other got hold of the four things first mentioned, can ever be completely a partaker of knowledge of the fifth. Further, on account of the weakness of language, these (i.e., the four) attempt to show what each thing is like, not less than what each thing is. For this reason no man of intelligence will venture to express his philosophical views in language, especially not in language that is unchangeable, which is true of that which is set down in written characters. Again you must learn the point which comes next. Every circle, of those which are by the act of man drawn or even turned on a lathe, is full of that which is opposite to the fifth thing. For everywhere it has contact with the straight. But the circle itself, we say, has nothing in either smaller or greater, of that which is its opposite. We say also that the name is not a thing of permanence for any of them, and that nothing prevents the things now called round from being called straight, and the straight things round; for those who make changes and call things by opposite names, nothing will be less permanent (than a name). Again with regard to the definition, if it is made up of names and verbal forms, the same remark holds that there is no sufficiently durable permanence in it. And there is no end to the instances of the ambiguity from which each of the four suffers; but the greatest of them is that which we mentioned a little earlier, that, whereas there are two things, that which has real being, and that which is only a quality, when the soul is seeking to know, not the quality, but the essence, each of the four, presenting to the soul by word and in act that which it is not seeking (i.e., the quality), a thing open to refutation by the senses, being merely the thing presented to the soul in each particular case whether by statement or the act of showing, fills, one may say, every man with puzzlement and perplexity.