Modals Lesson: Learn Must, Can’t, and Might! 

Lesson Overview

• What Are Modals? 
• Why Do These Modals Matter?
• Using Must to Express Certainty
• Using Can't to Express Impossibility
• Using Might to Express Possibility
• Comparing Must, Can't, and Might
• Practical Exercises

If you've ever been unsure whether to use "must," "can't," or "might" in a sentence, you're not alone. These three modal verbs can be tricky because they each express a different degree of certainty or possibility. Understand exactly how to use must, can't, and might when making guesses or deductions in English, choosing the correct modality.

What Are Modals? 

Modals are helping verbs (like can, could, will, must, might, etc.) that give additional meaning to the main verb. They don't take "-s" in third person, and they're followed by the base form of the main verb (no "to").

Why Do These Modals Matter?

Imagine you're guessing about something: is it true, not true, or maybe true? English has special helping verbs (modals) to express how sure or unsure we are about something. For example:

• "Where is Steven?"
  – *He might be in a meeting. (You're not sure – it's possible.)
• "Lucy has a name like ‘Luc' and a French accent."
  – *She must be French. (You're pretty sure – it's very likely true.)
• "That man looks way too short to be the basketball player we saw on TV."
  – *He can't be the one. (You're very sure he's not – it's almost impossible that he is.)

In each case, the bold words (might, must, can't) change the meaning of the sentence, telling us how confident the speaker is about the statement. These are modals of deduction or possibility, and mastering them helps you sound more natural and think critically in English.

Take This Quiz:

Modals 1 - for English 3 students

A Quick Overview of Meanings

Before diving deep, here's a quick snapshot of what each modal generally means in this context:

• Must = You feel sure something is true (based on evidence or logic).
• Can't = You feel sure something is NOT true (it's logically impossible, given the facts).
• Might = Maybe true, maybe not (it's possible but you're not sure).
  
  Keep these in mind-now let's explore each one with examples and explanations!

Using Must to Express Certainty

Use must when you have strong evidence or logical reasoning to conclude that something is true.

Structure: Subject + must + base verb

Examples:

• "I hear music from John's room. He must be home." (Music is evidence.)
• "He has a French accent and name. He must be French." (Strong logical assumption.)
• "You passed the test? You must be happy!" (Logical emotional response.)

Common Mistakes

• Avoid using "must" for slight suspicions: If you're not confident, use might. ("He must be the thief" is strong; if unsure, say "He might be the thief".)
• No past form of "must": Use must have + past participle for past deductions. ("She must have left already.")

Using Can't to Express Impossibility

Use can't when you are confident that something is not true.

Structure: Subject + can't + base verb

Examples:

• "Jill can't be in Italy; I just saw her in town." (Contradictory evidence.)
• "That can't be Diana's bag; hers is brown." (Logical deduction.)
• "You can't be serious!" (Common expression of disbelief.)

Common Mistakes

• Don't confuse "can't" with "must not": Mustn't usually means prohibition, not impossibility. ("You mustn't touch that!" means "You are not allowed to touch it", not "It's impossible to touch it.")
• Use "can't" for present deductions: "He can't be the thief." (Right) vs. "He mustn't be the thief." (Wrong.)
• Past deduction: Use can't have + past participle ("He can't have done it; he was with me.")

Take This Quiz:

Modals for English 3: Possibility and Probability

Using Might to Express Possibility

Use might when something is possible, but you are not sure.

Structure: Subject + might + base verb

Examples:

• "He might be in a meeting." (Possibility, but not sure.)
• "Be careful, you might fall!" (Warning about a possible event.)
• "I thought you might like to borrow my DVD." (Polite assumption.)

Common Mistakes

• "Might not" vs "Can't": Might not means uncertain, can't means impossible. ("She might not know." = Maybe she knows, maybe not. "She can't know." = We are sure she doesn't know.)
• No future form of "might": Use "might" for future possibilities: "I might go to the party tomorrow." (Not "I will might go.")

Comparing Must, Can't, and Might

Choosing between must, can't, and might depends on how confident you are about your statement and what evidence or context you have. It helps to ask yourself: "Am I sure it's true? Sure it's not true? Or unsure?" Here's a handy comparison:

Practical Exercises

1. Fill in the blanks with must, can't, or might.

1. You ______ be exhausted after running 10 miles!
2. That ______ be the answer. It doesn't make sense.
3. She ______ be at home, or maybe she went shopping.

2. Identify the modal:

• "He can't be the thief; he was with me all day."
• "She must be the new manager."
• "It might rain later."