modal verbs

possibility

must

should

could

might

may

would

(conditional)

that must be my delivery

that should be my delivery

(pouvait/pourrait)

Obligation

must

have to

only present

had to / will have to

I decide

imposed

"I must call my mother"

"I have to do my tax return"

"I have to file my taxes"

Prohibition

mustn't

can't

NO Obligation

don't have to

"you can come if you want, but you don't have to"

Permission

can

may

(+ polite)

you may be seated

you can sit down

advice

you could

you might

should

ought to

if were you...

necessity

need

(semi-modal)

I need / he needs

I don't need / I needn't

I needn't have done it

1st conditional

If I have the time I will help you

2nd conditional

If I had the time, I would help you

3rd conditional

If I'd had the time, I would have helped you

(I could have helped you)