L9 Grammar

until (or till) can be (A) a preposition (介系詞) and (B) a conjunction (連接詞)

(A)　until當介系詞
not…until + 時間的點
例: She doesn’t study until the last moment.
The lazy boy won’t wake up until 10 o’clock.

(B) until當連接詞
not…until + 子句
例: The firefighters did not leave until the fire was put out.
The boy did not tell the truth until he saw his mother.

補充
1. not 和 until不一定要連用，若動作是表示「持續或進行一段時間」亦可用之
例: Jane stayed in the library until eleven o’clock.
Alan will be away until Sunday.

2. not until 也可以放句首，但是句子要倒裝 (因為否定副詞放句首，句子倒裝)
例: They didn’t finish their report until Tuesday afternoon.
= Not until Tuesday afternoon did they finish their report.

例: Many people do not realize the importance of their health until they lose it.
= Not until many people lose their health do they realize the importance of it.

3. It is not until... that.... (分劣句)
It was not until yesterday that I noticed the new teacher.
It was not until I met you that I knew real happiness.
It was not until I visited him that I realized how serious his illness was.