knocked on / at the door

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00Only #2 is correct. 0-

0I try to do some corrections.02br
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00(i)He knocked at the door when entering the headmaster's office.02br
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00(iii) He knocked on the door while entering the office. 0-

0These are now grammatical, but somewhat illogical. (3) would be possible if he happened to find the door open. Otherwise it would have to be done in two stages, i.e., as in your (2).02br
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00In my opinion, (1) does not work, because "at the door" implies the door is closed (whereas in (3) it might be open.)0-

0 He knocked on / at the door before entering the office.02br
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00Does the sentence above mean he entered after knocking regardless of an answer?0-

0I honestly don't know what it means, N2g. I can't even say for sure that he entered. People often knock as a courtesy before entering, even when they have an understanding that they may enter at will.02br
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00I can't explain why, but I have the sense that "01u00at02u00 the door" would be the one to use if you wish to imply that he waited for a res

0I'm sorry. I forgot to remove 'at' when I copied the sentence over.02br
00I definitely agree with you that 'at' makes the sentence odd. I would 02br
00use on for sure in this context. 02br
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00So what do you think of the sentence with 'on'?02br
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00I think he entered after knocking. I wouldn't say he didn't enter.02br

0Most people would assume he entered, absent context to the contrary.02br
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00You see signs which read, "Knock, then enter." You see signs which read, "Knock before entering." Does the second one mean you're to wait for a response? "He knocked before entering." If he didn't get a response, did he enter?02br
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00"As he was making his way out of th

0From my understanding of before, I would say yes to all of your examples. But your tone02br
00sounds like the answer should be NO.02br
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00It seems like before is ambiguous after reading your examples.02br
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00For example,02br
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00The burglar took the two bottles of 50 year old wine before he escaped. (Did he escap

0Hi N2g,02br
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00I don't think "before" is ambiguous. I think the sentences which use it can be ambiguous. "He went to New York and then he went to Philadelphia" is not quite the same as "He went to New York before going to Philadelphia." In the second example, he may still be waiting to go to Philadelphia. The second sentence doesn't actually say he went to Philadelph

0Avangi, you do agree that your examples of presidents indicate that the events that come after before happened, right? That's exactly what I understand of before. However, I share your confusion in the philadelphia example. I can agree with you on this. However, the original example, the one we disagreed about, is what I find it hard to accept. This topic is really hard to grasp. How can learne