,

Every art and faculty contemplates certain things especially. When then it is itself of the same kind with the objects which it contemplates, it must of necessity contemplate itself also: but when it is of an unlike kind, it cannot contemplate itself. For instance, the shoemaker's art is employed on skins, but itself is entirely distinct from the material of skins: for this reason it does not contemplate itself. Again, the grammarian's art is employed about articulate speech; is then the art also articulate speech? By no means. For this reason it is not able to contemplate itself. Now reason, for what purpose has it been given by nature? For the right use of appearances. What is it then itself? A system of certain appearances. So by its nature it has the faculty of contemplating itself so. Again, sound sense, for the contemplation of what things does it belong to us? Good and evil, and things which are neither. What is it then itself? Good. And want of sense, what is it? Evil. Do you see then that good sense necessarily contemplates both itself and the opposite? For this reason it is the chief and the first work of a philosopher to examine appearances, and to distinguish them, and to admit none without examination. You see even in the matter of coin, in which our interest appears to be somewhat concerned, how we have invented an art, and how many means the assayer uses to try the value of coin, the sight, the touch, the smell, and lastly the hearing. He throws the coin down, and observes the sound, and he is not content with its sounding once, but through his great attention he becomes a musician. In like manner, where we think that to be mistaken and not to be mistaken make a great difference, there we apply great attention to discovering the things which can deceive. But in the matter of our miserable ruling faculty, yawning and sleeping, we carelessly admit every appearance, for the harm is not noticed.

When then you would know how careless you are with respect to good and evil, and how active with respect to things which are indifferent, observe how you feel with respect to being deprived of the sight of eyes, and how with respect of being deceived, and you will discover you are far from feeling as you ought to in relation to good and evil. "But this is a matter which requires much preparation, and much labor and study." Well then do you expect to acquire the greatest of arts with small labor? And yet the chief doctrine of philosophers is brief. If you would know, read Zeno's writings and you will see. For how few words it requires to say man's end is to follow the god's, and that the nature of good is a proper use of appearances. But if you say "What is 'God,' what is 'appearance,' and what is 'particular' and what is 'universal nature'? then indeed many words are necessary. If then Epicures should come and say that the good must be in the body; in this case also many words become necessary, and we must be taught what is the leading principle in us, and the fundamental and the substantial; and as it is not probable that the good of a snail is in the shell, is it probable that the good of a man is in the body? But you yourself, Epicurus, possess something better than this. What is that in you which deliberates, what is that which examines everything, what is that which forms a judgement about the body itself, that it is the principle part? and why do you light your lamp and labor for us, and write so many books? is it that we may not be ignorant of the truth, who we are, and what we are with respect to you? Thus the discussion requires many words.