虚拟语气：if 条件句三型——这条规则学生大多「听过」，却很少真正用对。原因往往不在记性，而在于汉语和英语在这里的底层逻辑不一样。这一讲把它拆开讲透。
为什么它值得单独讲
汉语的「如果……就」不区分真假，英语却要用不同形式表达与现在、过去、将来的事实相反，这是中国学生失分最集中的语法点之一。
规则
与现在事实相反：if + 过去式，主句 would + 原形；与过去事实相反：if + had + 过去分词，主句 would have + 过去分词；与将来相反：if + were to / should + 原形，主句 would + 原形。
中国学生的典型错误
把 would 放进 if 从句；或者在从句里用现在时表示虚拟。
错句对照
错：If I will have time, I would go.
对：If I had time, I would go.
为什么：从句不能用 will/would。
错：If I was you, I would apologize.
对：If I were you, I would apologize.
为什么：与现在相反用 were。
错：If I had studied, I would pass.
对：If I had studied, I would have passed.
为什么：与过去相反，主句用 would have done。
怎么练
① 背下 was → were 的固定例外。
② 先判断与哪个时间的事实相反，再套形式。
③ 把 If I were you 造句十句。
今天就能开始
今天就做一件事：在自己最近写的一段英文里，专门找一遍和「虚拟语气 if 条件句三型」有关的句子，按上面的规则逐句改。改不动的地方，说明规则还没吃透，回头再读一遍。