principle

(law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature).

“the principles of internal-combustion engines”

Rule of personal conduct.

A rule or law concerning a natural phenomenon or the function of a complex system.

“the principle of the conservation of mass”

“the principle of jet propulsion”

A basic generalization that is accepted as true and that can be used as a basis for reasoning or conduct.

“their principles of composition characterized all their works”

A basic truth or law or assumption.

“the principles of democracy”

A rule or standard especially of good behavior.

“a man of principle”

“he will not violate his principles”