Suppose、supposing 、 what if 和 should 的用法

Suppose、supposing 和 what if + 現在簡單式 － 表示對未來可能發生的事情提出建議。例如：

• Suppose we stop for a lunch break now? (我們現在歇一會兒吃午餐怎麼樣？)
• Supposing you fail the exam – what will you do then? (假設你考試不及格 － 那該怎麼辦？)
• What if you don’t pass your exams? (你要是考試不及格怎麼辦？)

Suppose、supposing 和 what if + 過去簡單式 － 表示比上述更不確定某事在未來是否可能發生。例如：

• Suppose I asked David to fix my computer? Do you think he’d do it? (如果我請大衛修理電腦怎麼樣？你想他會做嗎？)
  － 沒有 Suppose I ask David to fix my computer? 來得確定。
• Supposing you won the lottery, what would you do with the money? (假如你中了樂透，你會怎樣處置那筆彩金？)
  － 沒有 Supposing you win the lottery… 來得確定。
• What if the boss walked in here now and saw us? (如果老闆現在走進來這裡看到我們該怎麼辦？)
  － 沒有 What if the boss walks in here now and sees us? 來得確定。

Suppose、supposing 和 what if + 過去完成式 － 表示與過去事實相反，亦即這是一種過去的假設情況，實際上該事件並未發生。例如：

• Suppose I hadn’t gone to that concert with you. (如果我沒有跟你去聽那場音樂會會怎麼樣？) － 事實上，我有去聽那場音樂會。
• Supposing Cindy had broken up with her boyfriend. Would that have been a good idea? (如果辛蒂跟她男友分手，那會是個好主意嗎？) － 事實上，辛蒂沒有跟她男友分手。
• A: What if you’d decided to move to the United States! What city would you have chosen? (A：如果你已決定搬到美國！你會選擇哪個城市？) － 事實上，你並沒有決定搬到美國。
  B: I would have chosen Los Angeles. (B：我會選擇洛杉磯)
• Jason was supposed to hand in his paper, but he didn’t.
• Jason was going to hand in his paper, but he didn’t.
  Jason應該交上他的作業，但他卻沒有。
• The bus was supposed to arrive.
• The bus was going to arrive.
• 這班公車應該要到站了。

Should 應該 

用於現在式或未來式，表示應該做某件事，有責任與義務的意涵。
用於過去式: I should have Vp.p.，有後悔當初沒做什麼的意思。

• I should have told you that I love you.
• 我早該告訴你我愛你。
• She should be responsible for the task.
• 她應該負責這項任務。

You're not supposed (= allowed) to be ogling my friends.

She should be (= it was expected that she would be) here by no