The document describes different levels of certainty when making statements. It lists words that indicate something is certainly true (must be, can't be), probably true (probable, may be, might be), and possibly true (possible, might not be, may not be). It then provides examples of sentences using these different levels of certainty around whether something is, isn't, does, or doesn't involving people, places, things, or situations.

1. CERTAIN MUST (BE) CAN’T (BE)
PRESENT PROBABLE MAY (BE) MAY NOT (BE)
POSSIBLE MIGHT (BE) MIGHT NOT (BE)
1.- I’m sure John is worried about us.
John must be worried about us.
2.- Perhaps your father is at the station.
3.- I’m sure that John doesn’t live in this town.
4.- I’m sure everybody is at home now.
5.- Perhaps those aren’t our rooms.
6.- I’m sure the dog isn’t in the garden.
7.- I’m sure the children don’t like classical music.
8.- Perhaps that boy is German or Swedish.
9.- It’s possible that animals are happy in zoos.
10.- I’m certain everybody knows the answer.
11.- I’m certain her boyfriend is good-looking.
12.- Perhaps Mr. Jones has a dog.
13.- It’s possible that he practices too much exercise.
14.- I’m sure they are waiting for us.
15.- I’m sure those boots aren’t for climbing.
16.- It’s possible that doesn’t know where he is.