on principle

根据原则，按照原则

on display, on duty, on earth, on end, on file, on fire, on foot, on guard, on hand, on instalments, on instinct, on no account, on occasion, on one's guard, on one's head, on one's honor, on one's honour, on one's own, on one's way to..., on order that, on purpose, on relief, on sale, on schedule, on second thoughts, on the alert, on the analogy of, on the average, on the basis of, on the contrary, on the eve of..., on the first try, on the ground that, on the grounds of, on the impulse (of...), on the increase, on the lips of, on the nail, on the other hand, on the part of,