MAY
He was a stocky older man with a built-up shoe that clopped, and an eastern European haircut that may have been done at home.

MIGHT
"Do you think, Starling, he might have been interested to see if you'd rat him out when he sent you a letter of encouragement?" It might have been encrusted with diamonds. "Then Mr. Crouch's son might not have been involved?" said Harry slowly.

SHOULD
He should have been named Appall.

WOULD
You would have been wasted just like John Brigham. Otherwise she would have been summoned to the justice Department rather than the Hoover Building.
In any case, awkward questions would have been asked if she had gone back to the Ministry with the news that she had met you on her holidays. Krum, whom Harry would have thought would have been used to this sort of thing, skulked, half-hidden, at the back of the group. Fleur bent down, kissed Harry twice on each cheek (he felt his face burn and wouldn't have been surprised if steam was coming out of his ears again), then said to Ron, "And you too -- you 'elped -- "

MUST
Plans must have been changed after the blueprints were filed.

2.Marginals
a)Present / future reference

OUGHT TO
"You is ought to be ashamed of yourself, Dobby, talking that way about your masters!" Harry took the hint and sat down next to Percy, who was wearing brand-new, navy-blue dress robes and an expression of such smugness that Harry thought it ought to be fined.

b)Past reference
N/A

3.Modal idioms
a)Present / future reference

BE TO
Anything extended from the windows would have caught Starling's instant attention - she was wary of Crip revenge but silent ogling is to be endured.

b)Past reference
BE TO
Yet how could anyone think that, when he was facing competitors who'd had three years' more magical education than he had -- when he was now facing tasks that not only sounded very dangerous, but which were to be performed in front of hundreds of people?