Are core values the same as principles?

For me, principle is the word to describe your beliefs. People who act or live by principle have a (sometimes) written code of behaviour.I've always had ambivalent feelings about people and their principles... I sense a kind of rigidiity. And laziness. That is, if in doubt, check it out with your principles.Are core values the same thing? Why are they "core"? Are there surface values... values which are flexible, and core values are not flexible?Tom Law