Modals of Deduction Presentation

How it works

Guessing from evidence: She must be at work. He might be stuck in traffic. That can't be right. How sure you are, in one small word, now and in the past.

• She must be at work. Modals take the bare verb. Russian «должна быть» has an infinitive, and learners translate «быть» as to be; Spanish «debe de estar» has a de between the verbs, which turns into to.
• He must have gone home. After have, use the past participle (gone), not the past simple (went).
• He can't be at home — the lights are off. In British English mustn't means “not allowed”; for “I'm sure it isn't true”, use can't. Russian «не должно быть» invites mustn't. (American English sometimes says must not here, but can't is the safe choice everywhere.)
• It could be the courier — someone is at the door. Spanish «puede ser el mensajero» leads to can, but can talks about what is generally possible (It can be cold in May). For a guess about one situation, use could, might or may.

The form

Examples (1/2)

• 🚗She must be at work. Her car isn't here.
• 🚦He might be stuck in traffic.
• 🧮That can't be right. Check the numbers again.
• ✈️You must be tired after such a long flight.
• 🏢The office is dark. They must have gone home.

Examples (2/2)

• 💬She can't have seen my message yet.
• 🔑I might have left my keys at the gym.
• 📦Someone is at the door. It could be the courier.
• 😳He can't be serious about quitting!
• 🎉They must be having a party next door.

Which is right?

1. She must be at work.
2. She must to be at work.

Modals take the bare verb. Russian «должна быть» has an infinitive, and learners translate «быть» as to be; Spanish «debe de estar» has a de between the verbs, which turns into to.

Which is right?

1. He must have gone home.
2. He must have went home.

After have, use the past participle (gone), not the past simple (went).

Summary