C.S. Lewis pointed out that all men recognize the existence of a universal moral law, even if they do not follow it.  How does he know this?  Because all men offer excuses.  When someone offers an excuse for their actions, they are admitting that they have violated some higher law, but think their violation is justified.  They seek to justify their behavior, rationalizing their way out of the guilt they know is due them.  As J. Budzeszewski noted, “No one has ever discovered a way to merely set aside the moral law; what the rationalizer must do is make it appear that he is right.  Rationalizations, then, are powered by the same moral law which they twist.”