B1 · Intermedio Capítulo 31

Possibility and Probability

5 Reglas totales
51 ejemplos
6 min
Reglas en este capítulo Práctica rápida

Chapter in 30 Seconds

Master the art of expressing uncertainty and logical deductions with professional precision.

  • Differentiate between weak and strong possibilities using modal verbs.
  • Make logical deductions based on evidence using 'must' and 'can't'.
  • Use advanced probability adjectives and adverbs to sound more natural.
Stop guessing, start expressing levels of certainty.

Lo que aprenderás

Ever wonder how likely something is? This chapter helps you confidently discuss possibilities with may and might, and make logical deductions using must, so you can express yourself more precisely and naturally.

Learning Objectives

By the end of this chapter, you will be able to:

  1. 1
    By the end you will be able to: describe a 30-50% chance of an event happening using may or might.
  2. 2
    By the end you will be able to: conclude that something is definitely true or false based on evidence.
  3. 3
    By the end you will be able to: rank different outcomes from 'unlikely' to 'bound to' using non-modal structures.

Guía del capítulo

Overview

As a B1 English learner, you're moving beyond basic communication and starting to express more nuanced ideas. This is where understanding English possibility and probability becomes incredibly useful! Imagine you're making plans, discussing news, or even just wondering about the weather – knowing how to express how likely something is can really boost your confidence and make your English sound much more natural.
This chapter will equip you with essential tools to talk about uncertainty and make logical deductions.
We'll explore how to use modal verbs like may and might to express things that are simply possible, and how must helps you sound confident about a logical conclusion. You'll also learn handy phrases like may well and might well to express a higher degree of probability. By mastering these concepts, you'll be able to discuss potential outcomes, explain why you think something is true, and even confidently state when something just can't be!
These are all key skills for navigating a wide range of everyday conversations at the B1 English grammar level.
Being able to differentiate between something that *might* happen and something that *must* be true based on evidence will help you communicate more precisely. It's about adding depth to your English, allowing you to share your thoughts and reasoning in a clear and convincing way. Get ready to discuss possibilities and probabilities like a pro!

How This Grammar Works

Let's break down the core grammar rules for expressing possibility and probability in English. We use modal verbs to do this, and they always precede a base verb (the infinitive without 'to').
When you're talking about something that is possible, but not certain, you'll use may or might. They are largely interchangeable for present or future possibility. For example,
It may rain later
means there's a chance of rain.
Similarly,
She might be at the library
suggests it's a possibility, but you're not sure. These express general uncertainty or a 'maybe' situation.
Now, if you're quite sure about something based on evidence or logic, you use must. This isn't about obligation; it's about making a logical deduction. If your friend has been studying all night, you could say,
She must be tired.
You're almost certain based on the clues.
This is called the epistemic must. The evidence makes it highly probable.
To add a bit more strength to your predictions, you can use may well or might well. These phrases indicate that something is quite likely because it makes good sense or there are strong reasons for it. For instance, "If he doesn't study, he may well fail the exam" implies that it's a very probable outcome given his actions.
It's stronger than just may or might alone, suggesting a reasonable expectation.
Finally, when you're absolutely certain that something is logically impossible, you use can't. For example, if you see someone enter a room and then immediately leave through the same door, you could say, "She can't be in the room anymore." The evidence tells you it's impossible. It's the opposite of must for logical deduction.
These structures build on each other, allowing you to express varying degrees of certainty.

Common Mistakes

  1. 1✗ Using 'must' for permission instead of logical deduction in this context.
✓ He must be home, his car is in the driveway. (Correct: Logical deduction)
✗ You must go to the party. (Incorrect for probability; this is obligation. For possibility, you might say
You might go to the party if you want.
)
*Explanation:* Remember that the 'must' we're focusing on here is for making a logical guess, not for giving orders or saying something is required.
  1. 1✗ Confusing 'may' and 'might' for past possibility.
✓ She may have forgotten her keys. (Correct for past possibility)
✗ She might forget her keys yesterday. (Incorrect: 'Might' for past possibility needs 'have' + past participle)
*Explanation:* For past possibility or probability, you need to use may have + past participle or might have + past participle. The chapter focuses on present/future, but this is a common extension.
  1. 1✗ Using 'cannot' instead of 'can't' for logical impossibility in informal contexts.
✓ That can't be true! (Correct: Common and natural)
✗ That cannot be true! (Less natural in everyday, conversational English for this specific meaning, though grammatically correct)
*Explanation:* While 'cannot' is grammatically fine, 'can't' is much more common and natural when expressing logical impossibility in conversational English.

Real Conversations

A

A

The lights are off in John's office. He usually works late.
B

B

He must have left already. It's almost 7 PM.
A

A

Do you think Sarah will come to the party?
B

B

She said she was busy, so she might not make it. But she may well surprise us if her meeting finishes early.
A

A

I can hear music from next door.
B

B

Oh, that can't be my neighbour. He's on holiday in Spain this week!

Quick FAQ

Q

Can I use 'may' and 'might' interchangeably for possibility?

Yes, in most cases for present and future possibility, may and might are interchangeable. Some people feel 'might' expresses a slightly weaker possibility, but the difference is very subtle and often not significant in everyday conversation.

Q

How is 'must' for possibility different from 'must' for obligation?

Must for possibility (epistemic) means

I am almost certain based on evidence
(e.g.,
He must be rich; he drives a fancy car.
). Must for obligation means
It is necessary or required
(e.g.,
You must finish your homework.
). The context makes the meaning clear.

Q

Is 'may well' much stronger than 'may'?

Yes, may well expresses a higher degree of probability than just may. It suggests that something is quite likely because there's a logical reason or expectation for it to happen. It's like saying "it's very likely or it's probable."

Q

When should I use 'can't' instead of 'won't be able to' for impossibility?

Use can't when you're making a logical deduction that something is impossible based on facts or evidence ("That can't be true, I saw it myself!"). Use 'won't be able to' for future inability or lack of opportunity ("I won't be able to come tomorrow, I have an appointment.").

Cultural Context

Native English speakers use these modal verbs constantly to soften statements, express uncertainty, and convey different levels of conviction. In casual conversation, you'll hear might and can't a lot, as they add a natural flow. Must for deduction is also very common.
While may well and might well are perfectly natural, they tend to be slightly more formal or used when explaining a reasoned prediction. There aren't significant regional differences in the core usage of these modals, but the frequency of their use may vary slightly between individuals.

Ejemplos clave (8)

1

I `may go` to the gym after work, if I'm not too tired.

Puede que vaya al gimnasio después del trabajo, si no estoy muy cansado.

Posibilidad en Inglés: May y Might
2

They `might be` stuck in traffic, which is why they're late.

Podrían estar atrapados en el tráfico, por eso llegan tarde.

Posibilidad en Inglés: May y Might
3

Look at all the snow! It `must be` freezing outside.

¡Mira toda la nieve! Debe de hacer un frío tremendo afuera.

Deducción Lógica con 'Must' (Epistémico)
4

He's wearing a doctor's coat. He `must be` a doctor.

Lleva una bata de médico. Debe de ser médico.

Deducción Lógica con 'Must' (Epistémico)
5

She **may well pass** the exam; she studied all week.

Es muy probable que ella apruebe el examen; estudió toda la semana.

Potenciador de Probabilidad: May Well & Might Well
6

The package **might well arrive** tomorrow, as it shipped yesterday.

Es muy probable que el paquete llegue mañana, ya que fue enviado ayer.

Potenciador de Probabilidad: May Well & Might Well
7

That pizza place `can't be closed` already, it's only 8 PM!

¡Esa pizzería no puede estar cerrada ya, solo son las 8 PM!

Imposibilidad Lógica (¡No puede ser!)
8

My internet `couldn't have gone out`. I just paid the bill yesterday.

Mi internet no pudo haberse caído. Acabo de pagar la factura ayer.

Imposibilidad Lógica (¡No puede ser!)

Consejos y trucos (4)

💡

Usa para sugerencias amables

Usa 'might' para hacer sugerencias de forma amable. Es como endulzar un consejo para que suene menos exigente y más colaborativo:
You might want to consider this
.
frontend.learn_grammar.from_rule: Posibilidad en Inglés: May y Might
💡

¡Busca la evidencia!

Antes de usar 'must' para adivinar lógicamente, siempre asegúrate de tener pruebas sólidas. Cuanta más evidencia, más confianza puedes tener al usar 'must'.
The lights are off, so he must be asleep.
frontend.learn_grammar.from_rule: Deducción Lógica con 'Must' (Epistémico)
💡

Aumenta la fuerza de tus predicciones

Estos modales le dan confianza a tus pronósticos. Úsalos cuando tengas una buena razón para creer que algo pasará, haciendo que hables con más información:
The train may well be delayed due to the snow.
frontend.learn_grammar.from_rule: Potenciador de Probabilidad: May Well & Might Well
💡

Piensa en el opuesto

Si usarías must be para una deducción positiva fuerte (ej.,
He must be rich
), entonces can't be es su contraparte lógica negativa (ej., "He can't be poor"). Esto ayuda a reforzar la conexión lógica.
frontend.learn_grammar.from_rule: Imposibilidad Lógica (¡No puede ser!)

Vocabulario clave (6)

Evidence facts or signs that show something is true Likelihood the chance that something will happen Certain completely sure about something Possible able to be done or happen Impossible not able to occur or exist Predict to say what will happen in the future

Real-World Preview

coffee

Solving an Office Mystery

Review Summary

  • Subject + may/might + base verb
  • Subject + must + base verb
  • Subject + can't + base verb

Errores comunes

In English, we do not use 'must not' for logical deductions. We use 'can't' to say something is logically impossible.

Wrong: It must be not true.
Correcto: It can't be true.

Modal verbs like 'might' never take an 's' in the third person singular.

Wrong: He mights come to the party.
Correcto: He might come to the party.

Adverbs of probability like 'probably' usually go after the first auxiliary verb or before the main verb.

Wrong: Probably I will see you later.
Correcto: I will probably see you later.

Next Steps

You've unlocked a new level of English! Being able to speculate and deduce makes your conversations much more interesting. Keep practicing those 'must be' moments!

Look out the window and make 5 'must be' and 5 'might be' observations about people you see.

Continue to: Collocations and Word Partnerships

Práctica rápida (10)

Elige la forma correcta

She's always late, so she ___ miss the bus.

✓ Correct! ✗ Not quite. Correct answer: may well
May well expresa una fuerte probabilidad basada en su constante tardanza. May as well es para sugerencias, y well may es un orden de palabras incorrecto.

frontend.learn_grammar.from_rule: Potenciador de Probabilidad: May Well & Might Well

Choose the correct sentence.

Which is correct?

✓ Correct! ✗ Not quite. Correct answer: I will probably go.
Probably before verb.

frontend.learn_grammar.from_rule: Probability: Likely, Unlikely, Bound To, Definitely, Probably

Encuentra y corrige el error en la deducción lógica negativa.

Find and fix the mistake:

He must not be hungry; he just ate a huge burger.

✓ Correct! ✗ Not quite. Correct answer: He can't be hungry; he just ate a huge burger.
Para deducciones lógicas negativas, usamos 'can't' o 'couldn't', no 'must not'. 'Must not' implica prohibición.

frontend.learn_grammar.from_rule: Deducción Lógica con 'Must' (Epistémico)

Fill in the blank.

It is ___ to rain.

✓ Correct! ✗ Not quite. Correct answer: likely
Likely takes 'to'.

frontend.learn_grammar.from_rule: Probability: Likely, Unlikely, Bound To, Definitely, Probably

Encuentra y corrige el error

Find and fix the mistake:

If you don't save, you might as well run out of money.

✓ Correct! ✗ Not quite. Correct answer: If you don't save, you might well run out of money.
Might well indica una fuerte probabilidad de quedarse sin dinero como consecuencia de no ahorrar, mientras que might as well sugiere hacerlo como una opción.

frontend.learn_grammar.from_rule: Potenciador de Probabilidad: May Well & Might Well

Selecciona la frase que usa 'may' o 'might' correctamente.

Choose the correct sentence:

✓ Correct! ✗ Not quite. Correct answer: He may not understand the instructions.
'May not' va correctamente seguido de la forma base del verbo ('understand'). Las otras opciones tienen formas verbales incorrectas.

frontend.learn_grammar.from_rule: Posibilidad en Inglés: May y Might

Elige la forma correcta para completar la deducción lógica.

The lights are off and the door is locked. She ___ asleep.

✓ Correct! ✗ Not quite. Correct answer: must be
Para una deducción lógica en presente, usa 'must' seguido de la forma base del verbo 'to be'.

frontend.learn_grammar.from_rule: Deducción Lógica con 'Must' (Epistémico)

Encuentra y corrige el error en la frase.

Find and fix the mistake:

They might to forget about our meeting.

✓ Correct! ✗ Not quite. Correct answer: They might forget about our meeting.
Los verbos modales ('might') van seguidos directamente por la forma base del verbo principal ('forget'), sin 'to'.

frontend.learn_grammar.from_rule: Posibilidad en Inglés: May y Might

Elige la forma correcta para expresar imposibilidad lógica.

He's only 16, so he ___ a licensed driver yet.

✓ Correct! ✗ Not quite. Correct answer: can't be
Como tiene 16 años, es lógicamente imposible que sea un conductor con licencia (en la mayoría de los lugares). 'Can't be' expresa esta imposibilidad.

frontend.learn_grammar.from_rule: Imposibilidad Lógica (¡No puede ser!)

Fix the error.

Find and fix the mistake:

He is bound that he wins.

✓ Correct! ✗ Not quite. Correct answer: He is bound to win.
Bound to + infinitive.

frontend.learn_grammar.from_rule: Probability: Likely, Unlikely, Bound To, Definitely, Probably

Score: /10

Preguntas frecuentes (6)

La idea principal es expresar que algo es posible o probable, pero no totalmente seguro. Te permiten especular o suponer sin comprometerte con una afirmación definitiva, como 'It may rain later' o 'She might be busy'.
En la mayoría de los contextos modernos para expresar posibilidad, sí, son en gran medida intercambiables. Aunque 'might' a veces puede implicar una probabilidad ligeramente menor, la diferencia suele ser muy sutil y no se observa de forma consistente en el habla cotidiana.
Se trata de hacer una deducción fuerte y segura basada en la evidencia que tienes. Estás diciendo: 'Dado X, Y must be true' porque es la única conclusión lógica posible.
My phone is gone. I must have left it at home.
¡Muy seguro! Piensa en una probabilidad del 95-99%. Usas 'must' cuando la evidencia es tan fuerte que la conclusión parece casi innegable.
The lights are off, so he must be asleep.
(Las luces están apagadas, así que debe de estar dormido.)
May well significa que algo es muy probable o tiene una alta probabilidad, más que solo may. Implica una razón lógica para esa mayor probabilidad. Por ejemplo,
It may well rain later
(Es muy probable que llueva más tarde).
Ambos son bastante intercambiables para expresar alta probabilidad. Might well a veces puede ser un poco más tentativo o usarse para situaciones hipotéticas, pero el significado central de fuerte probabilidad permanece.
She might well be at home now
(Es muy probable que esté en casa ahora).
Capítulo anterior
The Second Conditional
Siguiente capítulo
Collocations and Word Partnerships
Volver a la hoja de ruta