我不能批准这个行为；这是个原则问题。

I cannot approve this action; it's a matter of ___principle.

对他而言，不走捷径是一项基本原则，即使在琐事上也是如此。

For him, not taking shortcuts was a fundamental ___principle, even in trivial matters.

出于原则，她拒绝了那笔捐款，认为其来源不道德。

She refused the donation on ___principle, believing it came from unethical sources.