In traditional ethics, the moral absolutes tend to be negative formulations of what we should never do. Thus in Plato’s Crito, Socrates says that we should never do what we know to be wrong. Of the Ten Commandments having to do with our relations with other people, six of them are negatives: do not kill, do not commit adultery, do not steal, etc. The natural law tradition seems to have as its main directive never intentionally to violate a basic good, such as life, truth, or friendship. And Kant’s second version of the categorical imperative stresses that we should never treat humanity, self of others, merely as a means to an end. All these negative formulations point out to us what would be wrong to do as well as what would be worthy of punishment. The positive commands, at least insofar as they have to do with our relations with other human beings, seem to be less absolute. That we should honor our mother and father, promote the basic goods, and treat people as ends are certainly obligations, but they are less strict, to use Kant’s terminology. It is worse to take a person’s life, for example, than to neglect to feed that person or provide for that person’s healthcare. Normally, we do not punish people for what they neglect to do (except if the need they refuse to meet is extremely dire); but we do think it right to punish people who kill or lie or steal.
However, this emphasis on negative obligations is somewhat odd since knowledge of what is right and good must logically precede knowledge of what is wrong and bad. We only know what a bad eraser is by knowing what a good eraser ought to be. We only know what a bad apple tree is by knowing how it falls short of a good one. And we only know that killing is bad because we know that life is good, and that lying is bad because truth and friendship are good. And the really good people we can think of do not just avoid violating goods but act for the sake of those goods. Think of Socrates: he did not sit around all day trying to avoid doing what was wrong or trying to avoid mistakes. On the contrary, he strove every day to be good and to know the truth. And it seems that he succeeded in avoiding wrongdoing precisely because he was focused on doing what was right.
I suppose one reason the negatives have been stressed is to counter our tendency to justify our behavior by our general intention to do good, to the point, sometimes, of neglecting the morality of how we go about achieving that good. For a good end does not justify an evil means; and one should never do evil so that good may come. As it could be argued that all our actions are for the sake of good ends, the key place to examine their morality is in the means we take to achieve our ends. These, like the ends, should always be good and never evil. It is clearly helpful for us to know, individually and socially, some absolute limits on our behavior, and these negatives provide those limits.
Still, it does not seem true to say that avoiding doing evil implies doing good, while it does seem true to say that thoughtfully seeking to do good keeps us from doing evil. Were we to be ever after the best actions—freely and intentionally—there would be little danger of our violating fundamental human goods. In general, refusing to be rude is less the essence of a good host than making every effort to be polite. And refusing to do evil is less the essence of a good person altogether than seeking to do what is good.
Another reason why we emphasis the negative prohibitions may be that it is hard to be good; and as we become better, we become more and more aware of our failings. It is more comforting to think of how we do not violate the absolutes, for doing so puts us in a positive light. But the reality is that becoming good is a difficult and never-ending process. And so we see Socrates claiming, and I think genuinely, that the more he knows about virtue, the less he is certain that he really knows it and lives it. This helps explain his on-going quest which, even in the face of death (not our hoped-for reward for being good) continues unabated. St. Paul admits the same kind of struggle to be good. As he gets closer to Christ, the living instantiation of all good, the evil in him is more and more evident. “I know that good does not dwell in me, that is, in my flesh. The willing is ready at hand, but doing the good is not” (Romans 7:18).
So it is that our knowledge of good is not only necessary for us to know what is evil, but it keeps us humble and persevering in our attempt to live well—to do good.