1. 시간 표현과 동사의 시제를 일치시킨다
We installed a new accounting system three years ago.
We have purchased three companies so far.
과거완료: by 1980, by the time + 과거
과거: three years ago, last week, in 1980, yesterday
현재완료: since 1990, for three years, so far
미래완료: by next July, by the time + 현재
2. 주절의 동사와 종속절의 동사를 일치시킨다
We have been friends since we met at school. (현재완료 + since + 과거)
She said that she couldn't come to the party on Friday. (조동사도 시제 일치)
3. 가정법: If 절의 시제와 주절의 시제 일치
a) 가정법 현재
If the company fails, we will lose our money.
b) 가정법 과거: 현재 사실
If I had enough money, I would travel around the world.
If I were you, I would buy a house. (인칭 무관 were)
c) 가정법 과거완료: 과거 사실
If I had been told that you would go, I would have gone too.
4. 시간/조건 부사절
*시간 부사절(when, after, before, until, once, as soon as): 미래 대신 현재, 미래완료 대신 현재완료
*조건 부사절(if, unless): 미래 대신 현재
a) I must get to the bank before it closes.
b) If we miss the train, we can get the next one.
5. 동사원형을 쓰는 특별 구문
a) demand, order, insist, require, request, suggest, propose, recommend + that + 주어 + 동사원형
The teacher demands that we be on time.
b) It is important/ necessary/ essential/ vital/ imperative/ advisable + that + 주어 + 동사원형
It is important that they be told the truth.