ought
1.ought是助动词，但在现代英语里它后面的不定式必须有to。例如：You ought to read it once more.
2.比较下面各句：
- You ought to do it today.
- You ought to do it tomorrow.
- You ought to have done it yesterday.（你昨天该做这个［可是你不曾做］。）
- When you came yesterday, I told you that you ought to do it at once.
- When you came yesterday, I told you that you ought to have done it the day before.
