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.
(..) What was that? There's a mental hospital right near here. All right, Elaine, David... ...I believe we have a deal here in principle. Arby's no more than once a month... ...and in exchange Elaine comes to your softball game... ...and doesn't read a book. (..)1998 TvShow: Seinfeld Title: The Dealership Season: 9 Episode 11