Francis Schaeffer noticed long ago that a generation had grown up that didn't use the word truth to mean the same thing previous generations did, and things have only gotten weirder since then. Sin doesn't seem to be a concept most kids in college have a handle on--even some of the religious ones. But ask them this: "Have you ever done something that, if you knew your friend had done it, would break your friendship?" It'll take them a while to sift through that question, but sooner or later something will come to mind. And when they do they're not apt to admit it to you, but they've recognized sin.