And, Socrates continues, it is a given that the possibility exists that our friends may be in fact bad, or unjust, men; and it can be that our enemies may be good men, no matter the reason that we have incurred their enmity. Thus it is that, according to Polemarchus' definition of justice, in our ignorance we may do good to bad men and harm to good men, and surely this is not the achievement of justice.
And so Polemarchus agrees to another re-definition: Justice may be defined as doing good for friends who are in fact good men and in punishing those who are in fact bad men.
But again, Socrates demurs: He argues that returning evil for evil does not constitute justice. Analogically, he argues that if we harm a horse, we make that horse a worse horse; if we harm a dog, we simply achieve a worse dog. If we agree that a good man is a just man, then a worse (unjust) man cannot be said to have been made better if we do evil to him; such a course would only serve to make him more unjust. Thus Socrates argues that we cannot achieve justice by doing evil to men who are already evil, and unjust. And Polemarchus concurs with this conclusion.
