should 和 be supposed to v. 在中文都被翻成 “應該"，所以區別在哪裡?
be supposed to 表示的是一種預期 (expectation) 的情況：
-現在式的 be supposed to v. 指的 “應該", 則是指預定的計畫, 或別人預期我們要做到的事
-過去式的 be supposed to 意為「大家預期發生的事，但實際上卻沒發生」，因此相當於 should have + P.P. 或 ought to have + P.P. 「本該發生的事，但實際上卻沒發生」。
A: The train is supposed to be on time.
B: Yeah, it’s never late.
A: Johnny, you are supposed to finish your homework before you watch TV!
B: Of course, mom. I will finish my homework first before I watch cartoons.
A: You were supposed to call that girl! I even gave you her phone number!
B: I’m sorry. I just didn’t have the courage to call.
A: Class was supposed to begin at 10: 00, but it didn’t begin until 10: 15.
Class should have begun at 10: 00 (but it didn’t begin until 10: 15).
Class ought to have begun at 10: 00 (but it didn’t begin until 10: 15).
be supposed to 除了上述的意思外，還有一個常見的意思，就是「一般認為」(be generally believed/considered)。
Elephants are supposed to be afraid of mice.
Elephants are generally believed to be afraid of mice.
It is generally believed that elephants are afraid of mice.
(Yes, I know that elephants aren’t really afraid of mice.)
should/ought to 指的 “應該", 是說做這樣的事是有好處的 (ought to 的語氣比 should 來得強)*
You should go get new glasses. You can’t see clearly with the ones you have now.
You should study hard now. The final is only a few days away.
或者表示義務, 責的任應該, 應當
You should help these people. It’s your duty as a doctor.
A teacher should also dedicate himself or herself to education.
*should 和 ought to 的用法比較: