Àķ˹·Æ¶ûµÂ know and unknown
±¾Ìû×îºóÓÉ ¤è¤í¤·¤¯ ÓÚ 2013-8-18 22:17 ±à¼Reports that say something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know," Rumsfeld told a news briefing. "We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know."
A press briefing given by former US Defense Secretary Donald Rumsfeld on February 12, 2002.
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