His investment strategy is based on the 'principle' that the stock market offers the best returns for long-term investors.
As 'a matter of principle', he would not accept the gift. [=he did not feel that it was right to accept the gift]
She refused 'on principle' [=because of her beliefs] to give toy guns to the children.
(..) - Objection. - Watch it, counselor. I'm trying very hard, Judge. Try harder, counselor. It seems basic to our constitutional principles that the extent of the right to assemble, and demonstrate and march along the highway in a peaceful manner ought to be commensurate (..)2014 Selma
(..) This ain't right. What's that? This necktie. It's not right. Well, it's not a necktie, dear. It's an ascot. Yes, but generally the same principles should apply, shouldn't they? It's not right. It's not right, or you don't like it? I don't like how this looks. Looks distinguished and debonair to me. (..)2014 Selma