Ability
If I had gone to the sales, I'm sure I ______ something. (to buy)
If I had gone to the sales, I'm sure I would have bought something.
Clare was very upset that you didn't go to her birthday party. You_____ (to go).
Clare was very upset that you didn't go to her birthday party. You should/ ought to have gone.
The lights are out. They______ to sleep. (to go)
The lights are out. They must have/ might have gone to sleep.
We ______ Dave to the party if we had known he was in town. (to invite)
We would have invited Dave to the party if we had known he was in town.
We ______ so much food. We can't eat it all (to order)
We shouldn't have/ needn't have ordered so much food. We can't eat it all.