example dialog:

"yes, yes, it's your job. I know that."

Can I just say "I know" instead of "I know that"?

another one: do I say

It is very pretty. Where did you buy?
where did you buy it?


(1) You can say "I know" or "I know that.
(2) You really need the "it' here. "Where did you buy?" sounds incomplete, leading to another question, "Where did I buy what?"

I think the difference may be that in sentence 2, you're referring to a thing, so the "it" is standing in for whatever was bought, while in question 1 "it's your job" is an abstraction, so somehow it's OK to just say, "I know."

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  • Know in (1) refers to the clause that comes right before it, so there's no pronoun necessary -- it's essentially a transform of I know it's your job. In (2), however, the object of know is not indicated, as you point out, so something must be provided. – John Lawler Feb 23 '15 at 17:17
  • I agree with David. – Michael Rize Feb 24 '15 at 9:24
  • My answer may be correct in saying that "that" is needed in one sentence and not in the other, but John Lawler analyzed and explained the difference. – David Garner Feb 24 '15 at 10:34
  • One sentence," John is reading a book.Where did he get?" Can I omit the pronoun "it" because" a book" is just right before "Where did he get?" – celia qiang Feb 25 '15 at 3:01
  • No, that sounds wrong. I see your point: you've just mentioned the book, so what else could "get" be referring to? But you need to say "Where did he get it?", where the pronoun "it" is standing in for "the book". – David Garner Feb 25 '15 at 9:15

In dialog, you would usually say "I know that" as a simple statement. "I know" would be accompanied either by a gesture such as holding up your hand with the palm toward the other person to signify that he doesn't need to say any more, or by significant stress on the words to send the same message.

This may not apply outside the US.

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