1) a fundamental truth or proposition that serves as the foundation for a system of belief or behaviour or for a chain of reasoning. (Oxford Dictionaries Online 2012)
2) a rule or belief governing one’s behavior. (Oxford Dictionaries Online 2012)
(1) and (2) Oxford Dictionaries Online S.v. "Principle" Accessed February 20, 2012. Available at http://oxforddictionaries.com/definition/concept.
A principle is a rule of conduct or behavior. To take this further, a principle is a “basic generalization that is accepted as true and that can be used as a basis for reasoning or conduct.” (WordWeb.com) A principle can also be thought of as a “basic truth or law or assumption.” [ibid.]
Principles depend on concepts in order to state a “truth.” Hence, principles and concepts go hand in hand; principles cannot exist without concepts and concepts are not very useful without principles to help guide the proper way to act (Lawson and Martin 2008).
Lawson, H., and J.N. Martin. 2008. "On the Use of Concepts and Principles for Improving Systems Engineering Practice". Proceedings of the 18th Annual International Council on Systems Engineering (INCOSE) International Symposium, 5-19 June 2008, Utrecht, The Netherlands.