参考书本及公众号链接：
纯条件虚拟，主将从现
if 一般现在，主 will + do./may/can/should/must/ought to
与现在事实相反的虚拟
if 一般过去，主 would + do./might/could/should/ought to
与过去事实相反的虚拟
if had done，主 would + have done./might/could/should/ought to
与将来状况相反的虚拟
If …should.万一…
高可能性：if should do，主 will + do.
/may/can/should/must/ought
to
低可能性：if should do，主 would + do.
/might/could/should/ought
to
If should do + 祈使句
If he is here, I will beat him.
如果他在这儿，我会揍他。
If he were here, I would beat him.(but he is not here).
如果他现在在这儿，我会揍他，但他现在不在这儿。
If he had been here, I would have beat him. (but he wasn't not here).
如果他当时在这儿，我会揍他，但他当时不在这。
If he should be here, I would/I will beat him.
万一他在这儿，我会揍他。
If I should be late, be sure to wait for me.
万一我迟到，务必要等我。
应注意事项：
强烈与真理相反的虚拟语气。
if were to do，主 would +
do./might/could/should/ought to
The sun doesn't rise in the west.
If the sun were to rise in the west, how surprised these sunflowers would be.
if的省略。
何秀华：had, should, were
时态不一致的假设。
从句与过去事实相反had done，主句与现在事实相反would。
if had done，主 would
+ do now/today./might/could/should/ought to
If I had started saving then, I would be able to buy a car now.
可替代if的其他连词，从句一般现在时。
Once一旦, when当, before, as soon as一旦, unless,
in case(that),in case of+名词, on condition that,
provided/ providing(that), so long as只要, as long as只要.
but for…若非/要不是…
与现在事实相反，若非…就…
If it were not [that(一般现在)]/[for + 名词]，｜
Without/but
for + 名词，｜主 would + do./might/could/should/ought
to
与过去事实相反，若非当时…就…
If it had not been [that(一般过去)]/[for + 名词]，｜
Without/but
for + 名词，｜主 would + have done./might/could/should/ought
to
If it were not that he works hard, I wouldn't like him.
=If it were not for his hard work, I…
=Were it not for his hard work, I…
=But for his hard work, I…
要不是他努力工作，我才不会喜欢他。
If it had not been that he lent me the money, I could not have bought that book.
=If it had not been for the money he lent me, I…
=Had it not been for the money he lent me, I…
=But for the money he lent to me, I…
要不是他当时借钱给我，我无法买到那本书。
lest…(Should)…以免…
I arrived on time lest he (should) be angry.
我准时到达，免得他生气。
as if…=as though…仿佛…
a.极大的可能→动词用一般时
It looks as if it's going to rain.
b.与现在事实相反→as if + 一般过去时
Mr wang loves me as if I were his own child.
c.与过去事实相反→as if + 过去完成时
He looked as if nothing had happened.
What if … should…？
/What if…一般现在…
要是…的话怎么样？要怎么办？
What if he should come？
What if he comes？
It is time that + 一般过去时
该是…的时候了
It's time we did it.
If only…要是…就好了
只能用一般过去时或过去完成时。
If only he were here.
I wish he were here.
要是他现在在这里就好了。
If only I had known it earlier.
I wish I had known it earlier.
要是我早点知道这件事就好了。
Wish (that)虚拟语气
wish(that)从句没有一般现在时
I wish (that)… 真希望…就好了
=I would rather (that)…
与现在事实相反→从句一般过去时
I wish he were here.
It's too bad that he is not here.
与过去事实相反→从句过去完成时
I wish I had studied harder when young.
hope
现在情况，
I hope he is safe.
将来情况，
I hope he will be back.
进行情况，
I hope they are having a good time.
完成情况，
I hope they have finished the work.
I hope (that) may& 祈使句
I hope you may pass the exam.
=May you pass the exam.
wish/hope 异同
异：表祝福
wish 双宾→that从句
I wish you a good time.
I wish my parents Longevity.
I hope you (may) have a good time.
I hope my parents can live long.
同：
wish/hope to do
wish/hope for 期望获得…
对过去事物的猜测的三种句型
Must have done, 一定曾经…
may have done,可能曾经…
cannot have done.不可能曾经…
didn't need to do.不必…同时也没有做。
needn't have done.不必…但却做了。
As I had enough money, I didn't need to borrow any from him.
Since you had enough money, you needn't have borrowed money from me, but why did
you still borrow some？
意志动词 +(should)
建议，suggest, recommend,
advise, urge(呼吁), purpose,
move(提议).
要求，Ask, desire, demand,
require, request, insist.
命令，Order, command.
规定，Rule, regulate, stipulate
主张，Advocate, maintain.
They suggested that he (should) come home on time.
suggest暗示, insist坚信, maintain坚决认为 + that 一般时.
His words suggested that he wasn't telling a lie.
他的话中暗示她绝不是在说谎。
He insists that the job isn't so difficult as one may think.
他深信这份工作没有一般人想象的那么困难。
Insist on doing.坚决要…(固执)
Persist in doing.从事…很执着(努力不放弃)
John insisted on going fishing even though a typhoon was coming.
Peter persisted in handling the problem all by himself.
有必要的adj that +(should)。
necessary, important, essential, imperative urgent, desirable, recommendable, advisable.
有必要的，很重要的，不可或缺的，有绝对必要的，紧急的，合意的，值得推荐的，明智的
It's necessary that he (should) work hard.
他必须努力工作。
意志名词 + that从句作同位语 +(should) 。
It's my suggestion that he (should) study abroad.
As it were 可以说是…(插入语)
=so to speak.