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How we must adapt preconceptions to particular cases.—­What is the first business of him who philosophizes?  To throw away self-conceit ([Greek:  oiaesis]).  For it is impossible for a man to begin to learn that which he thinks that he knows.  As to things then which ought to be done and ought not to be done, and good and bad, and beautiful and ugly, all of us talking of them at random go to the philosophers; and on these matters we praise, we censure, we accuse, we blame, we judge and determine about principles honorable and dishonorable.  But why do we go to the philosophers?  Because we wish to learn what we do not think that we know.  And what is this?  Theorems.  For we wish to learn what philosophers say as being something elegant and acute; and some wish to learn that they may get profit from what they learn.  It is ridiculous then to think that a person wishes to learn one thing, and will learn another; or further, that a man will make proficiency in that which he does not learn.  But the many are deceived by this which deceived also the rhetorician Theopompus, when he blames even Plato for wishing everything to be defined.  For what does he say?  Did none of us before you use the words good or just, or do we utter the sounds in an unmeaning and empty way without understanding what they severally signify?  Now who tells you, Theopompus, that we had not natural notions of each of these things and preconceptions ([Greek:  prolaepseis])?  But it is not possible to adapt preconceptions to their correspondent objects if we have not distinguished (analyzed) them, and inquired what object must be subjected to each preconception.  You may make the same charge against physicians also.  For who among us did not use the words healthy and unhealthy before Hippocrates lived, or did we utter these words as empty sounds?  For we have also a certain preconception of health, but we are not able to adapt it.  For this reason one says, Abstain from food; another says, Give food; another says, Bleed; and another says, Use cupping.  What is the reason? is it any other than that a man cannot properly adapt the preconceptions of health to particulars?

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How we should struggle against appearances.—­Every habit and faculty is maintained and increased by the corresponding actions:  the habit of walking by walking, the habit of running by running.  If you would be a good reader, read; if a writer, write.  But when you shall not have read for thirty days in succession, but have done something else, you will know the consequence.  In the same way, if you shall have lain down ten days, get up and attempt to make a long walk, and you will see how your legs are weakened.  Generally then if you would make anything a habit, do it; if you would not make it a habit, do not do it, but accustom yourself to do something else in place of it.