Would

We use would ('d) I wouldn't when we imagine a situation or action (= we think of something that is not real):

It would be nice to buy a new car, but we can't afford it.
I'd love to live by the sea.
A: Shall I tell Chris what happened?
B: No, I wouldn't say anything.
(= I wouldn't say anything in your situation)

We use would have (done) when we imagine situations or actions in the past (= things that didn't happen):

They helped us a lot. I don't know what we'd have done
(= we would have done) without their help.
I didn't tell Sam what happened. He wouldn't have been pleased.

Compare would (do) and would have (done):

I would call Lisa, but I don't have her number. (now)
I would have called Lisa, but I didn't have her number. (past)
I'm not going to invite them to the party. They wouldn't come anyway.
I didn't invite them to the party. They wouldn't have come anyway.

We often use would in sentences with if (see Units 38-40):

Compare will ('ll) and would ('d):

I'll stay a little longer. I've got plenty of time.
I'd stay a little longer, but I really have to go now. (so I can't stay longer)
I'll call Lisa. I have her number.
I'd call Lisa, but I don,t have her number. (so I can't call her)

Sometimes would/wouldn't is the past of will/won't. Compare:

present	past
TOM: I'll call you on Sunday.	=> Tom said he'd call me on Sunday.
AMY: I promise I won't be late.	=> Amy promised that she wouldn't be late.
LISA: Damn! The car won't start.	=> Lisa was annoyed because her car wouldn't start.

Somebody wouldn't do something = he/she refused to do it:

You can also use would to talk about things that happened regularly in the past:

When we were children, we lived by the sea. In summer, if the weather was fine, we would all get up early and go for a swim. (= we did this regularly)
Whenever Richard was angry, he would walk out of the room.

With this meaning, would is similar to used to (see Unit 18):