Advanced grammar

English Power Verbs: How to Master Can, Could, Should, and Must

Hello everyone, it's Alex! Today, I want to talk about some of the most powerful words in the entire English language. I call them the "Power Verbs." You might know them as Modal Verbs. For a long time, I was so confused by them. What's the real difference between 'Can' and 'Could'? When should I use 'Should' and when 'Must'? It felt like a complicated secret.

But then I realized they aren't complicated. They are like a team of superheroes! Each verb has its own special power that changes the meaning of a sentence. One gives you the power of Ability, another gives you the power of Advice. Once you understand their powers, using them becomes easy and fun. Today, I'm opening my personal files and sharing the "secret profile" of each of these heroes, one by one. Let's get started!

📜 The 3 Golden Rules 📜

Before we meet the heroes, you MUST know their three unbreakable rules. These rules apply to ALL of them!

• Rule #1: They Never Change. They never add '-s', '-ed', or '-ing'. (We say "He can swim," not "He cans swim.")
• Rule #2: They Are Followed by the Base Verb. The verb that comes after them is always the simple, "infinitive" form (like 'eat', 'go', 'play'). (We say "You should stop," not "You should to stop.")
• Rule #3: They Are Special Helpers. To make a question, you just invert them with the subject. (e.g., "Can you swim?")

Okay, now that we know the rules of their universe, let's meet the first and most famous hero!

Meet the Heroes: Official Profiles

🦸‍♂️ HERO PROFILE: CAN

This is the "Superman" of the group. His main power is making things possible. He is all about ability and opportunity.

POWER #1: ABILITY (What you *can* do)

This is his most famous power. Use 'can' to talk about skills and what you are physically or mentally able to do.

• I can speak two languages.
• A bird can fly, but a dog can't.
• He can run very fast.

POWER #2: PERMISSION (What you are *allowed* to do)

You can also use 'can' to ask for or give permission in a friendly, informal way.

• Asking: Can I go to the bathroom, please?
• Giving: Yes, you can borrow my pen.
• Refusing: No, you can't have another cookie.

Hero Weakness (Negative Form): The negative form is cannot (one word) or, more commonly, the contraction can't.
Example: I can't understand this problem.

🧐 HERO PROFILE: COULD

Think of 'Could' as the older, more polite, and more thoughtful version of 'Can'. He is a master of time and possibility.

POWER #1: PAST ABILITY (What you *could* do)

This is his primary power. 'Could' is the past tense of 'Can'. Use it to talk about abilities you had in the past.

• When I was young, I could climb trees.
• She could play the piano when she was five.
• I couldn't swim last year, but now I can.

POWER #2: POLITE REQUESTS (The "Gentleman" Power)

This is why he's a gentleman! Asking with 'Could' is much more polite and formal than asking with 'Can'.

• Could you please pass the salt? (More polite than "Can you...")
• Could you help me for a minute?

POWER #3: POSSIBILITY (What *might* happen)

Use 'Could' to talk about something that is possible, but not 100% certain. It shows a weak possibility.

• Be careful, you could fall. (It's a possibility)
• It could rain tomorrow, so bring an umbrella.

Hero Weakness (Negative Form): The negative form is could not (two words) or the contraction couldn't.
Example: I couldn't find my keys this morning.

👨‍🏫 HERO PROFILE: SHOULD

This hero is the team's advisor. He is not a boss, but he is very wise. His power is giving good advice and talking about what is "right" or "correct".

POWER #1: ADVICE (What is a *good idea* to do)

This is his main job. Use 'Should' to give someone advice or to suggest what you think is the best action.

• You look tired. You should go to sleep.
• It's a great movie. You should watch it.
• He should study more if he wants to pass the exam.

POWER #2: EXPECTATION (What is *supposed* to happen)

You can also use 'Should' to talk about something you expect to happen.

• I sent the package last week. It should arrive today. (I expect it to arrive)
• He left an hour ago. He should be home by now.

Hero Weakness (Negative Form): The negative form is should not or shouldn't. It's used to give advice *against* doing something.
Example: You shouldn't eat so much fast food.

💪 HERO PROFILE: MUST

This is the strongest hero on the team. He is not for gentle advice; he is for power, rules, and certainty. He is the boss!

POWER #1: STRONG OBLIGATION (What you *have to* do)

Use 'Must' when something is a rule, a law, or a very strong command. It's not optional.

• You must wear a seatbelt in the car. (It's the law)
• Students must finish their homework. (It's a strong rule)
• I must stop smoking. (A strong personal decision)

POWER #2: LOGICAL CONCLUSION (What is *almost certain*)

This is a very smart power. You use 'Must' when you look at a situation and make a conclusion that you are 99% sure is true.

• He has been working for 12 hours. He must be tired. (It's a logical conclusion)
• She didn't answer her phone. She must be busy.

⚠️ A CRITICAL DIFFERENCE! ⚠️

This is the most important trick to learn. The negatives of 'Must' are tricky!

• Mustn't = It is forbidden! Do NOT do this. (You mustn't smoke here.)

• Don't have to = It is not necessary. You have no obligation. It's optional. (You don't have to come if you're busy. You can if you want.)

This is a very common mistake for learners, so remember this difference!

Bonus Level: The Hero Sidekicks

You've met the main team! Now let's quickly meet their "sidekicks" or partners. These are also modal verbs and they are very useful.

Partner: MAY (The Formal Twin of 'Can')

'May' is used for **formal permission**. It's much more polite than 'Can'. Use it with your boss or a professor.

• May I ask a question, professor?

Partner: MIGHT (The Weaker Twin of 'Could')

'Might' is used for **weak possibility**. It's even less certain than 'Could'.

• I don't know, I might go to the party, or I might just stay home. (It's 50/50)

Partner: WILL (The Hero of the Future)

You already know this one! 'Will' is used to talk about the **future** and to make promises.

• I will call you tomorrow. (A promise)
• It will be sunny this weekend. (A prediction)

Partner: WOULD (The Hero of Imagination)

'Would' is a bit more advanced, but it's used for **polite offers** and **imaginary situations** (hypotheticals).

• Would you like a cup of tea? (A very polite offer)
• If I were rich, I would buy a big house. (An imaginary situation)

Test Your New Powers!

Okay, hero-in-training! Let's see if you've mastered these new powers. Choose the best modal verb for the sentence. Click to see the answer!

1. You look sick. You ______ go to the doctor. (can / should)

Answer: should (This is strong advice!)

2. My grandfather ______ run a marathon, but now he can't. (can / could)

Answer: could (This is an ability in the past.)

3. You ______ be quiet in the library. It's a rule. (must / should)

Answer: must (This is a strong rule/obligation.)

My Final Encouragement

See? These "Power Verbs" aren't so scary after all. Once you learn their personalities and their special powers, you can use them with so much confidence. You now have the tools to give advice, talk about your abilities, and be extra polite. Practice using one new power every day, and soon you will be a modal verb superhero!

Your Turn! 💬

Which "Power Verb" do you think is the most useful? Write one sentence in the comments using Can, Could, Should, or Must. I would love to see your examples!