principle

她基于原则不穿皮草。

She doesn't wear fur ___on ___principle.

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.

他们，基于原则从不喝酒，那天晚上却喝醉了。

They, who ___on ___principle never drank alcohol, got drunk that night.