Modals for Modals for CertaintyCertainty

To think about ‘degrees of certainty’

Present Time: Present Time: “Why isn’t Susie in the class?”“Why isn’t Susie in the class?”

Degrees of Certainty

Modals (+V.inf)

100% sure She is sick.

95% sure She must be sick.

50% sure or less (possibly, maybe*,

perhaps)

She may be sick.

She might be sick.

She could be sick.

Present Time Negative:Present Time Negative:“Why doesn’t Susie eat anything?”“Why doesn’t Susie eat anything?”

Degrees of Certainty

Modals (+V.inf)

100% sure She isn’t hungry.

99% sure(impossibly)

She couldn’t be hungry.She can’t be hungry.

95% sure(a best guess)

She must not be hungry

50% sure or less(possibly, maybe*,

perhaps)

She may not be hungry. She might not be hungry.

Past Time: Past Time: “Why wasn’t Susie in the class?”“Why wasn’t Susie in the class?”

Degrees of Certainty

Modals (+have + V3)

100% sure She was sick.

95% sureShe must have been sick.

50% sure or less (possibly, maybe*,

perhaps)

She may have been sick.

She might have been sick.

She could have been sick.

Past Time Negative:Past Time Negative:“Why didn’t Susie eat anything?”“Why didn’t Susie eat anything?”

Degrees of Certainty

Modals (+have + V3)

100% sure She wasn’t hungry.

99% sure(impossibly)

She couldn’t have been hungry.She can’t have been hungry.

95% sure(a best guess)

She must not have been hungry

50% sure or less(possibly,

maybe*, perhaps)

She may not have been hungry. She might not have been hungry.