SOCRATES: And further, the instruments by which the instruments are procured, and so on, going back from stage to stage ad infinitum,--are not all these, in your opinion, necessary in order to carry out the work? CRITIAS: We may fairly suppose such to be the case. SOCRATES: And if a man has food and drink and clothes and the other things which are useful to the body, would he need gold or silver or any other means by which he could procure that which he now has? CRITIAS: I do not think so. SOCRATES: Then you consider that a man never wants any of these things for the use of the body? CRITIAS: Certainly not. SOCRATES: And if they appear useless to this end, ought they not always to appear useless? For we have already laid down the principle that things cannot be at one time useful and at another time not, in the same process. CRITIAS: But in that respect your argument and mine are the same. For you maintain if they are useful to a certain end, they can never become useless; whereas I say that in order to accomplish some results bad things are needed, and good for others. SOCRATES: But can a bad thing be used to carry out a good purpose? CRITIAS: I should say not. SOCRATES: And we call those actions good which a man does for the sake of virtue? CRITIAS: Yes. SOCRATES: But can a man learn any kind of knowledge which is imparted by word of mouth if he is wholly deprived of the sense of hearing? CRITIAS: Certainly not, I think. SOCRATES: And will not hearing be useful for virtue, if virtue is taught by hearing and we use the sense of hearing in giving instruction? CRITIAS: Yes. SOCRATES: And since medicine frees the sick man from his disease, that art too may sometimes appear useful in the acquisition of virtue, e.g. when hearing is procured by the aid of medicine. CRITIAS: Very likely. SOCRATES: But if, again, we obtain by wealth the aid of medicine, shall we not regard wealth as useful for virtue? CRITIAS: True. SOCRATES: And also the instruments by which wealth is procured? CRITIAS: Certainly. SOCRATES: Then you think that a man may gain wealth by bad and disgraceful means, and, having obtained the aid of medicine which enables him to acquire the power of hearing, may use that very faculty for the acquisition of virtue? CRITIAS: Yes, I do. SOCRATES: But can that which is evil be useful for virtue? CRITIAS: No. SOCRATES: It is not therefore necessary that the means by which we obtain what is useful for a certain object should always be useful for the same object: for it seems that bad actions may sometimes serve good purposes? The matter will be still plainer if we look at it in this way:--If things are useful towards the several ends for which they exist, which ends would not come into existence without them, how would you regard them? Can ignorance, for instance, be useful for knowledge, or disease for health, or vice for virtue? CRITIAS: Never.