He would vote against it on principle.

他会依据原则投票反对它。

He doesn't invest in the arms industry on principle.

他根据自己的信条，不投资军火工业。

He acted always on principle.

他总是按原则办事。

I refuse to go there, on principle.

我原则上拒绝到那儿去。

I disagreed your idea on principle.

原则上，我不同意你的主意。