Post edited 3:44 pm - 13/11/2009 by Rook

Uses of should:

Usually, should is used as a weaker form of must. It is used to indicate an obligation or duty concerning the future:

I should study harder.

We should do everything we can to help them.

Should I ask them to join us for lunch?

Should + have is used to indicate that the obligation was not fulfilled in the past:

I should have studied harder.

We should have done everything we could have, to help them.

Should I have asked them to join us for lunch?

Should is also used to make a prediction about the future:

Tomorrow's match should be interesting.

The sun should rise in about 16 minutes from now.

Uses of would:

Would is used to indicate that something will happen in the future:

He said he would read my article and send me his comments
within a week.

I would never ask him for money.

Would is used to indicate conditionality:

If they were to invite me, I would probably go.

You would still be working for us if you had not lied on your resume.

Would + have is used to indicate past conditionality:

If she had practiced a little harder, she would have won the match.

I would have invited him to the party if he had not made fun of me.

Would is used to discuss a past habit:

My brother would often talk in his sleep.

Would is used to make a request or ask a question:

Would you help your brother carry these books?

Would you mention this site to your friends?

Note: the questions above are a little ambiguous (i.e., it is not clear if they’re being asked neutrally [simply to get information] or if they contain implied requests). Adding "please" will remove the ambiguity and make the request explicit:

Would you please help your brother carry these books?

Would you please mention this site to your friends?