Make logical guesses about others: modal verbs of deduction.

We use modal verbs to make logical guesses about situations — how certain we are based on the evidence. "Must" expresses strong certainty something is true, "can't" expresses strong certainty something is false, and "might/could/may" express real uncertainty.

Why this matters This lesson connects directly to your progress: it covers must and can't: strong certainty; might, could, may: real uncertainty; past deductions: modal + have + past participle. Mastering this content lets you move forward confidently, and reinforces patterns you'll use again later. Take time to review every example before moving to the assessment — repetition is what actually locks knowledge in long-term.

01

What will you be able to do?

The goals of this lesson.

02

Before you start

You already know modal verbs for possibility (might, could, may). This lesson adds modals of deduction — using logic to guess what's probably true ("She must be tired").

03

Must and can't: strong certainty

"Must" means you're almost certain something is true, based on evidence. "Can't" means you're almost certain something is false — it's the negative equivalent of "must" for deduction (not "mustn't").

ModalCertaintyExample
must + base verbalmost certainly trueShe must be tired.
can't + base verbalmost certainly falseThat can't be true.

Examples

She must be tired after that long flight.
Present (must)
He must be at work right now.
Present (must)
They must be very happy with the news.
Present (must)
This must be the right address.
Present (must)
You must be joking.
Present (must)
She can't be at home — the lights are off.
Present (can't)
He can't be serious about this plan.
Present (can't)
That can't be true.
Present (can't)

04

Might, could, may: real uncertainty

These three are roughly interchangeable and express genuine uncertainty — you have no strong evidence either way.

Examples

She might be running late.
Present (might)
He could be at the gym right now.
Present (could)
They may be having dinner already.
Present (may)
It might be too late to call her.
Present (might)

05

Past deductions: modal + have + past participle

To make a deduction about the past, add "have" + past participle after the modal — "must have", "can't have", "might have", "could have", "may have".

FormExample
must have + p.p.She must have left already.
can't have + p.p.He can't have said that.

Examples

She must have left already — her car is gone.
Past (must have)
He must have forgotten about the meeting.
Past (must have)
They must have taken a different route.
Past (must have)
She can't have finished the report already.
Past (can't have)
He can't have said that — it's not like him.
Past (can't have)
They can't have left without saying goodbye.
Past (can't have)
She might have missed the bus.
Past (might have)
He could have forgotten his phone at home.
Past (could have)
They may have gotten stuck in traffic.
Past (may have)
The lights are on, so someone must have come home.
Past (must have)

06

Reading

Read the text and answer the questions. You can try as many times as you want.

Detective Reyes examined the empty apartment carefully. "The window is open, so the thief must have entered this way," she said. "But there's no sign of forced entry, so they can't have broken the lock. They must have had a key."

Her partner disagreed. "That can't be right — nobody else has a key except the owner." "Well, someone might have copied it," Reyes replied. "Or the owner may have forgotten to lock the door. We can't be sure yet, but we'll figure it out."

1. How does Reyes think the thief entered?

2. Why does she say they can't have broken the lock?

3. What does Reyes think the thief must have had?

4. Does her partner agree?

5. What is one possibility Reyes suggests?

💪 You're reasoning and speculating like a native speaker now. Review this lesson, or keep advancing your B2 skills!

07

Fill in the Blanks

Usa las pistas para completar cada palabra en inglés. Sin calificar — repite las veces que quieras.

08

Key Points

The essentials of this lesson, summarized.

09

Vocabulary in This Lesson

Key terms to remember.

tired
adjective

in need of rest; lacking energy

"She must be tired after that long flight."

Collocations: look tired, feel tired, get tired

Traduccióncansado/a
work
noun / verb

a job or place of employment; or to do a job

"He must be at work right now."

Collocations: at work, out of work, work overtime

Traduccióntrabajo, trabajar
happy
adjective

feeling or showing pleasure or contentment

"They must be very happy with the news."

Collocations: happy about, perfectly happy, happy medium

Traducciónfeliz, contento/a
address
noun

the details of where someone lives or something is located

"This must be the right address."

Collocations: home address, change of address, permanent address

Traduccióndirección
joking
verb (progressive)

saying something as a joke, not seriously

"You must be joking."

Collocations: just joking, joking aside, joking around

Traducciónbromeando
home
noun

the place where someone lives

"She can't be at home — the lights are off."

Collocations: at home, work from home, feel at home

Traduccióncasa, hogar

10

Build the Sentence

Tap the words in the correct order to form the sentence. Ungraded — repeat as many times as you like.

11

Choose the Correct Verb

Tap the correct verb form to complete each sentence. The other options are conjugations from other tenses — on purpose, so you learn to tell them apart.

It might too late to call her

This must the right address

They must have a different route

They may have stuck in traffic

He must have about the meeting

13

Assessment

You need at least 80% to unlock the next lesson. You can retake it as many times as you want — your best score is saved.

1. "They may be having dinner already." — which one is correct?

2. Select the correct match for: "She might be running late."

3. Select the correct match for: "He could have forgotten his phone at home."

4. "They may have gotten stuck in traffic." — which one is correct?

5. Which option matches: "She can't have finished the report already."?

6. Select the correct match for: "They must have taken a different route."

7. Which option matches: "He can't be serious about this plan."?

8. Which option matches: "They must be very happy with the news."?

9. Which option matches: "It might be too late to call her."?

10. What does this mean: "The lights are on, so someone must have come home."?

Review — Lesson 43 What matches: "The letter was written by Sarah."?

Review — Lesson 43 What matches: "My car was stolen last week."?

14

Summary and next step

You now make logical deductions with modal verbs. Next lesson: modal perfects, for speculating about the past.

🗣️ Practice out loud

Use the conversational tutor to practice this topic.

Open the tutor

15

Games

Practice this lesson's vocabulary with a word search and flashcards. Ungraded — play as many times as you like.

Word Search

Tap the first and last letter of a hidden word to find it. Los términos de varias palabras van sin espacios en el tablero (ej. "give up" aparece como GIVEUP).

Flashcards

Elige la respuesta correcta. Si aciertas, la tarjeta queda lista por hoy; si fallas, vuelve a aparecer pronto para reforzarla. Tu progreso se guarda en este dispositivo.

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