Q: Many people say “I don’t know that” at the beginning of a statement. In my opinion, “I don’t think that” makes more sense. For example, in a recent interview Roger Clemens said, “I don’t know that I have anything left to prove.” It sounds like he’s stating a fact while claiming not to know it. Is this usage correct?
A: Roger Clemens’s use of “know” isn’t unusual. In fact, you might say it’s been known for quite some time. The Oxford English Dictionary quotes similar usages dating back to the year 1000.
From then until now, according to the OED, one definition of “know” has been “to be cognizant, conscious, or aware of (a fact); to be informed of, to have learned; to apprehend (with the mind), to understand.” The dictionary notes that the usage is seen in “various constructions,” including “with dependent statement, usually introduced by that.”
So a sentence like “I don’t know that I have anything left to prove” can be read as “I’m not aware that I have anything left to prove.”
One other point. An obscure definition of “know,” dating back to the year 1200, is to acknowledge. This cobwebbed usage sounds very similar to the sense in which modern speakers say things like “I don’t know that I agree with you.”
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