What is the correct usage of phrase you don't know what you don't know? In (2), however, the object of. It's not just you that don't know.
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Also explain the difference between the two, thanks. Why it is know of in this sentence? Can it be used in formal conversation/writing?
Earth is the only planet we know of where life exists.
I know (about) this difficulty/problem. Alright, well, for example, like on saturdays, y’know, what i liked to do. Therefore, saying did you know asks if you have previously known something. Recently one of my friends told me that there is distinct difference between 'know of something' and 'know about something' expressions.
'know of' is used when you have personal. Do is the present tense, so saying do you know would ask if you currently know. However, i am having trouble figuring out why (or whether) this is the correct way to write the sentence,. This sentence is from the commentary of planet earth.
I saw this sentence in the book 1q84:
Can it be know about？. Possibly, i do know that can in fact only be used, when, you are answering the question of whether or not you know the issue at hand (or your knowledge has been called in. In the first sentence, it seems to me that to know expresses that the speaker experienced the problem/difficulty.
