The key answer of exercise 6

1

• might try catching is a suggestion
• needn't catch shows a lack of necessity
• won't catch expresses impossibility (It is too late to catch the bus.)

2

• Can explains possibility
• must be able to is deduction
• not supposed to explains the rule (No Smoking)

3

• ought and 's supposed express an expectation
• 's likely to is a possibility (less likely than the first two)

4

• can't is deduction (She is younger.)
• must is deduction (She is older.)
• 's bound to is a deduction (The speaker thinks she is probably older than him.)

5

• didn't need to get shows lack of necessity (It wasn't required, and we don't know if the marks were good or not.)
• needn't have got shows lack of necessity (We got good marks, but it wasn't necessary.)
• were supposed to get shows that according to the rules, we needed good marks

6

• is bound to is a certain prediction
• is supposed to is talking about what should happen
• must is talking about deduction

7

• Do you need to talks about necessity
• Are you likely to talks about probability
• Will you talks about willingness