What's the grammatical difference between 'should' and 'could'?

Question

I need examples too.

Answer 1

Both past tense, auxillary (need another verb with it) verbs
aux.v.
Past tense of shall
Used to express obligation or duty: You should send her a note.
Used to express probability or expectation: They should arrive at noon.
Used to express conditionality or contingency: If she should fall, then so would I.
Used to moderate the directness or bluntness of a statement: I should think he would like to go.
aux.v.
Past tense of can1
Used to indicate ability or permission in the past: I could run faster then. Only men could go to the club in those days.
Used with hypothetical or conditional force: If we could help, we would.
Used to indicate tentativeness or politeness: I could be wrong. Could you come over here?

Answer 2

COULD

Could can be used to ask for permission, to make a request and express ability in the past. Compare the following:
--Could I borrow your black dress for the formal dinner tomorrow?
--Could you do me a favor and pick Pete up from the station?

SHOULD

Should is used to give advice and make recommendations and to talk about obligation, duty and what is expected to happen. Reference is to the present and the future. Should is similar to must but is not as strong as must:
--You should always wear a helmet when you go out cycling on busy roads.
--Once the pack is opened, the cooked meat inside should be consumed within three days.

Answer 3

should is being use for giving an order or command. example: you should keep up the good work. while could is just the same in using the word can. example: (in INDEPENDENT CLAUSE) it could stand alone ulinke the dependent clause...

Answer 4

An example of proper use.

You could use a dictionary and, indeed, truly should.

Answer 5

should= a feeling of responsiblity, I really should apologize for what I said.
could= is more an option, I could appologize, but I really feel like what I said was the truth.

Answer 6

coulda, shoulda, woulda.