What is good and what is evil? There are two answers to this question.

1. First it may be said: good is that which you consider to be good, and the effect of which is agreeable to you both in its beginning and end. Evil is that which you consider to be evil and the effect of which is disagreeable in the beginning as well as in the end. If good and evil have no agreeable or disagreeable effect at first, or have a contrary effect at the beginning, whether they are really agreeable or disagreeable will appear in the end.
2. The second answer is that all things that seem good and evil are the opposite ends of one line, and it is difficult to say where evil ends and good begins, for these are comparative terms; a lesser good would seem evil when compared with a greater good, and the lesser evil in comparison with the greater evil would appear good. If there were no evil, good would not have been valued. Without injustice, justice would not have been appreciated. Therefore the whole of life's joy is expressed in duality.