Principles prove, and they are not proved.

原则用来证明而本身不需进行证明。

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While Mr. Obama surely does not seek a return to these earlier forms of conflict, a return to first principles such as hostis humani generis may prove a better guide for a nation at war than a president's day-to-day instincts.

WSJ: John Yoo: Obama, Drones and Thomas Aquinas