Grade 12, English, Unit 12, 1 C - Grammar (Modal Auxiliaries - Can, Should, and Must)
Presentation: Modal Auxiliaries — Can, Should, and Must
Good morning everyone.
Today, I am going to give a presentation about modal auxiliaries, especially can, should, and must.
These three modal verbs are very common in English. They help us express ideas such as ability, permission, possibility, advice, obligation, necessity, and prohibition.
By the end of this presentation, we should be able to understand their forms, uses, and differences, and use them correctly in sentences.
1. What Are Modal Auxiliaries?
First, what are modal auxiliaries?
Modal auxiliaries, or modal verbs, are helping verbs that express the speaker's attitude toward an action or situation.
Some common modal verbs are:
can, could, may, might, should, must, will, would, and shall.
Today, we will focus on:
CAN – SHOULD – MUST
One important rule is that a modal verb is followed by the base form of a verb, also called the infinitive without "to."
For example:
I can swim.
You should study.
We must leave.
We do not say:
❌ I can swims.
❌ You should studied.
❌ We must to leave.
The correct forms are:
✅ I can swim.
✅ You should study.
✅ We must leave.
2. CAN
Let's begin with can.
The basic structure is:
Subject + can + verb-infinitive
For example:
She can speak English.
The negative form is:
Subject + cannot/can't + verb-infinitive
For example:
She cannot speak French.
The question form is:
Can + subject + verb-infinitive?
For example:
Can you swim?
There are four important uses of can in the lesson.
3. CAN — Permission
First, can can be used to ask for or give permission.
For example:
Can I take your umbrella?
Here, the speaker is asking for permission to take the umbrella.
We can also use can to give permission:
You can use my computer.
This means:
You have permission to use my computer.
4. CAN — Physical Ability
Second, can expresses physical ability.
For example:
He can lift that heavy box.
This tells us that he has the physical ability to lift the box.
We can also say:
She can run very fast.
I can swim.
They can carry the table.
5. CAN — Acquired Skill
Third, can can express an acquired skill or learned ability.
For example:
Madan can play the piano very well.
This means Madan has learned the skill of playing the piano.
Other examples are:
She can speak three languages.
He can drive a car.
My brother can play the guitar.
6. CAN — Possibility
Fourth, can can express possibility.
For example:
The solution to the problem can be found.
This means that finding the solution is possible.
Another example:
Accidents can happen at any time.
So, remember that can can express:
Permission + Ability + Skill + Possibility
7. SHOULD
Now let's move to should.
The basic structure is:
Subject + should + verb-infinitive
For example:
You should study every day.
The negative form is:
Subject + should not/shouldn't + verb-infinitive
For example:
You shouldn't waste your time.
The question form is:
Should + subject + verb-infinitive?
For example:
Should I study tonight?
8. SHOULD — Necessity and Advice
The first important use of should is to say that we think an action is necessary, appropriate, or a good idea.
For example:
You should eat a healthy breakfast.
This means eating breakfast is considered beneficial or advisable.
Another example is:
Students should respect their teachers.
Here, the speaker believes that respecting teachers is the appropriate thing to do.
9. SHOULD — Obligation and Advisability
The lesson also uses should to express obligation and advisability.
For example:
You should get up early to study for your exam.
This can express advice or something that is considered necessary for a particular purpose.
Another example is:
You should work hard if you want to get distinctions.
This is mainly advice.
We can remember:
SHOULD = advice, recommendation, or what is considered appropriate
Examples:
You should exercise regularly.
You should drink enough water.
You should revise before an examination.
10. MUST
Now let's discuss must.
The basic structure is:
Subject + must + verb-infinitive
For example:
You must arrive two hours before your flight.
The negative form is:
Subject + must not/mustn't + verb-infinitive
For example:
You mustn't enter the meeting room without permission.
The question form is:
Must + subject + verb-infinitive?
For example:
Must I complete this assignment today?
11. MUST — Necessity and Obligation
The first important use of must is to express necessity or obligation in the present.
For example:
You must arrive two hours before your flight.
This means arriving two hours early is necessary.
Other examples:
Students must wear their school uniforms.
You must submit your assignment on time.
All applicants must take an entrance examination.
The word must generally expresses a stronger requirement than should.
12. MUST — Negative Consequence
The lesson also gives another use of must.
For example:
You must nourish yourself emotionally as well as physically and mentally, or else you will get sick.
Here, must expresses a strong necessity.
The idea is:
If you do not take care of yourself, there may be a negative consequence.
Another example:
You must follow the instructions, or you may make a mistake.
13. MUST NOT — Prohibition
One of the most important points is the difference between must and mustn't.
Mustn't means something is prohibited or not allowed.
For example:
You mustn't enter the meeting room without permission.
This means:
You are not allowed to enter the meeting room without permission.
Other examples:
Students mustn't leave the examination hall without permission.
You mustn't smoke in public areas.
Visitors mustn't touch the equipment.
So:
must = necessary
but
mustn't = prohibited
14. CAN, SHOULD, AND MUST — Comparison
Now let's compare the three modal auxiliaries.
CAN
Expresses:
Permission
Ability
Skill
Possibility
Example:
You can use my phone.
SHOULD
Expresses:
Advice
Recommendation
Advisability
What is considered appropriate
Example:
You should study regularly.
MUST
Expresses:
Strong necessity
Obligation
Requirement
Prohibition when used as mustn't
Example:
You must wear a seat belt.
You mustn't smoke here.
15. CAN, SHOULD, MUST — Strength
We can also think about the strength of these modal verbs.
CAN
It is possible / allowed.
SHOULD
It is advisable.
MUST
It is necessary or required.
For example:
You can attend the meeting.
This means you are allowed to attend.
You should attend the meeting.
This means attending is recommended.
You must attend the meeting.
This means attending is required.
This difference is very important.
16. Exercise from the Lesson
Let's look at the exercise in the lesson.
We need to choose the appropriate modal verb: must, can, or should.
1. All applicants ______ take an entrance examination.
The correct answer is:
must
Because taking the examination is a requirement.
All applicants must take an entrance examination.
2. ______ you ride a motorcycle?
The answer is:
Can
Because we are asking about ability.
Can you ride a motorcycle?
3. You look pale and sick. You ______ go and see a doctor.
The answer is:
should
This is advice.
You should go and see a doctor.
4. The elders of this generation ______ teach their children to be polite.
The appropriate answer is:
should
It expresses what is considered appropriate or advisable.
The elders of this generation should teach their children to be polite.
5. You ______ not smoke in public areas.
The answer is:
must
Because smoking is prohibited.
You must not smoke in public areas.
6. The police have done as much as they ______ to find the missing boy.
The answer is:
can
This means they have done as much as they are able to do.
The police have done as much as they can to find the missing boy.
7. Students ______ not leave the examination hall without permission.
The answer is:
must
Students must not leave the examination hall without permission.
It expresses prohibition.
8. Although she is young, she ______ speak three languages.
The answer is:
can
Because this expresses ability or skill.
Although she is young, she can speak three languages.
9. All passengers ______ wear seat belts when they are in a car or plane.
The answer is:
must
Because wearing a seat belt is presented as a requirement.
All passengers must wear seat belts when they are in a car or plane.
10. If you are disturbed by this ringtone, you ______ change it.
The answer is:
can
Because the person has the option or ability to change it.
If you are disturbed by this ringtone, you can change it.
17. Six Example Sentences
Now, let's make our own sentences using these three modal auxiliaries.
CAN
I can speak English.
Can I use your dictionary?
SHOULD
You should review your lessons every day.
Students should respect one another.
MUST
You must complete your homework.
Students mustn't cheat in examinations.
18. Important Grammar Rule
Finally, remember one very important grammar rule:
After can, should, and must, we use the base form of the verb.
For example:
can go
should study
must work
Not:
❌ can goes
❌ should studied
❌ must working
Also, modal verbs do not change according to the subject.
We say:
I can swim.
He can swim.
She can swim.
They can swim.
Not:
❌ He cans swim.
The same applies to should and must:
He should study.
She must leave.
We do not add -s to the modal verb.
19. Conclusion
To conclude, today's lesson has focused on three important modal auxiliaries: can, should, and must.
CAN is mainly used for:
permission, ability, skill, and possibility.
SHOULD is mainly used for:
advice, recommendation, and advisability.
MUST is mainly used for:
necessity, obligation, and requirements.
And remember:
MUSTN'T means prohibition — something is not allowed.
The basic structures are simple:
Subject + can + V-infinitive
Subject + should + V-infinitive
Subject + must + V-infinitive
If we understand the meaning and strength of these modal verbs, we can use them accurately in both speaking and writing.
Thank you for listening.
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