should 本应该做某事却没有做,表示责备和遗憾.
如; You should ahve told me the news eariler.
would 表示与事实相反.
1.If I were a bird, I would be happy.(与现在事实相反)
2. If I had told him the news, he would have cried..(与过去事实相反)
3. If I were to go tomorrow, I would take a plane..(与将来事实相反)