MODALS PERFECT INFINITIVES

Modal Perfect Infinitives• These modal verbs refer to the past.• Sometimes describe unreal situations

Obligation/ Prohibition

• To express obligation(with modal perfect infinitives) we will use SHOULD instead of Must

- You should have taken my advice seriously. Now you are in big trouble.

• To express prohibition. We will use SHOULDN’T instead of MUSTN’T

- You shouldn’t have answered in such a way. You even made her cry.

Certainty• We will use MUST when we are sure

that something has happened.- She must have missed her train.

She’s always in time.- She must have overslept.- She must have been a good

teacher.

Certainty• When we are sure about something

which is IMPOSSIBLE.- She can’t have broken your

pencilcase. She is always very careful with other people’s things.

- It can’t have been my dog. He is adorable.