英文文法問題should should've

In sentences of Hypothetical Conditions the past subjunctive is used in the "if" clause and should+the infinitive are used in the main clause.Sentences of this kind refer to present time,past time.
(a)Present time--Verb in Main clause should+bare infinitive:-
NB:-should+bare infinitive means should pass---see---say--- know---have=buy=cut etc.
If Jeffrey were here, he would know the answer.
If I had the money, I should buy a new pair of shoes.
If the grass need cutting, I should cut them.
If the shoes suit me, I should buy them.
(b)Past Time--Verb in Main clause should have+past participle:-
Here are sentences expressing hypothetical conditions in the past time; implied a negative.
If Jeffrey had worked hard in the past, he would have passed.(Implied Negative....but he didn't work hard.)
If you had asked me in the past, I should have helped you.(Implied Negative....but you didn't ask me.)
If I had had the money, I should have bought a house.(Implied Negative....but I hadn't the money.)
If the shoes had suited me stylishly, I should have bought them.(Implied Negative.....but they didn't suit stylishly.)
If you had not helped me, I should never have done that heavy work.(Implied Negative work......should never have+past participle=done.)
If you hadn't told me about it, I should never have gone to see it.(Implied Negative.....should never have+past participle=gone.)

2013-12-20 15:57:31 補充：
should:-what is necessary or desirable;ought to;eg:-should call the police.
should have thought:-expressing opposite meaning;expressing surprise;ought not;should have done=haven't done in reality.

簡單黎講,
should 係應該
例: She should not go to that concert because she did not finish her homework.

should've = should have= 原本應該
例: She should've finish her homework before going to the concert.

Should is you 應該做一件事 or 怎樣做那件事. It is present tense.E.g. You should exercise at least three times a week to keepyourself healthy.You should handle this matter with extreme caution.Should have is you 應該做一件事, but you didn’t do it. It’s a conditional tense. It has a littlesense of regret.e.g. I should have known better not to ask him for assistance. I should have devoted my full efforts into my studies. That means you will get better results if youwere more diligent, but instead you didn’t.

Another possibility is that 'should' is a modal verb and 'have' is the main verb.
e. g. They should have a second chance.

2013-12-20 15:48:21 補充：
I think Jenkin has given a complete and clear answer to what jef****** meant to ask. jef****** obviously wanted to know the difference between 'should' and 'should have' when used with a main verb. I just want to remind jef****** that in some cases, both of them are auxiliary verbs.

簡單用一個動詞do作例子解釋吧

do是指做一件事

should do = 應該要去做的 - 例如: you should do x = 你應該是要去做的
你寫的should've是should have done = 應該是做了的 - 例如: you should have done x = 你原應是要去做了(完成)的x，暗示現實是你沒有做。

用法上
should是正面指出應該要做的
should've是反面指你是應該已經做了(暗指事實或結果是沒有做到或沒有做過)