There is an old story—probably apocryphal—in which a college professor and a student are arguing. They were not arguing in the abusive style to which we have become accustomed; they were having more of a scholarly debate.
“There is no such thing as cold.” The class broke into laughter.
“Have you looked outside?” a student replied. “It’s snowing and the temperature is below freezing. Of course there is cold!”
“I can understand your confusion,” replied the professor, “but let’s explore that thought. What is the opposite of cold? It’s heat, of course. Can we agree that heat exists?” The class murmured their acquiescence. “If you’ve ever stood outside near an air conditioner that was running, what did you feel? Heat produced by the Bernoulli process or heat removed by a heat pump.
“Therefore, cold is the description we apply to the absence of heat.
“Similarly, dark is merely the absence of light. Light exists—we can see it, we can measure it, just like heat. Remove the light and we call it darkness.” The sea of faces indicated that they understood what he was saying, although they did not yet accept it as fact or thoroughly understand it.
“Can anyone give me a similar example?” the professor asked. One student—the shyest one in class—raised her hand. The professor had never even heard her speak before, so he pointed to her. She stood up and waited a second before she started to speak.
“By your logic, there is no such thing as evil. Evil is the absence of good.”
I find this a most interesting perspective. If true, then the only effective way to combat evil is by doing good.