Must – Logical Conclusion

LBCC ESL Online Learning

Introduction

This lesson introduces the modal “must” and how it’s used to make logical conclusions. This lesson includes two interactive quizzes.

“Must” is a modal or helping word. “Must” can be used to mean several things but only making logical conclusions is covered in this lesson. “Must”, like all modals, follows two main grammatical rules.

· Modals are never conjugated.
I must …
He must …
She must …
It must …
You must …
They must …
We must …

· The verb that follows the modal is always in simple form.
I must be …, I must not have, I must think
He must be…, He must not have, He must think
She must be …, She must not have, She must think
It must be …, It must not have, It must think
You must be …, You must not have, You must think
They must be …, They must not have, They must think
We must be …, We must not have, We must think

Must & Must Not

The modal “must” can be very confusing. Must, as well as must not, are usually used as modals of expectation or obligation. When must, or must not, is used as a modal of probability, it means that the speaker is not absolutely certain (he or she might be wrong). Must means that the speaker is about 90% certain. Must not means that the speaker is about 95% certain. Must and must not can be used in the simple present tense, the present continuous tense, the present perfect tense, and the present perfect continuous tense. The best way to demonstrate these uses is with examples.

Simple Present Tense
Must and must not are used with the simple present tense to show probability of a current situation. Grammatically, must and must not are followed by the simple form of the verb. *Please remember that the simple form of am, is, and are is be!

Teacher: Where is Maria?
Student: Maria must be sick. She always comes to school.

The student is saying that Maria is probably sick. The student does not know for certain if she is ill.
Boss: Why haven't we received the equipment?
Employee: It must not be ready yet.

The employee does not know that the equipment is not ready. This is just one possibility. It is also possible that the shipping company has lost it. The employee just does not know.

Present Continuous Tense
Must and must not are used with the present continuous tense to show probability of a situation that is happen right now. Grammatically, must and must not are followed by the word "be" and than the -ing form of the verb.

Friend One: Why isn't Bob answering the door?
Friend Two: He must be sleeping.

Friend Two does not know for that Bob is sleeping. Friend Two is guessing. It is also possible that Bob is listening to music with headphones or any other number of things.
Friend One: Why isn't Raul's car in the parking lot?
Friend Two: He must not be working today.

Once again, Friend Two does not know for certain why Raul's car isn't in the parking lot. It is possible that his car wouldn't start and he took the bus.

Present Perfect Tense
Must and must not are used with the present perfect tense to show probability of a situation that has already happened. Grammatically, must and must not are followed by the word "have" and then the past participle form of the verb.

Student One: Where are your books?
Student Two: I must have left them in the classroom.

Student One and Student Two are talking about a past action. Student Two is not certain. Student Two thinks that he/she left his/her books in the classroom.
Teacher: Why did Fusae fail the test?
Student: She must not have studied.

The student is saying that Fusae probably did not study. The student does not know this. This is just one possibility. It is also possible that Fusae was not feeling well when she took the test. The student just does not know.

Present Perfect Continuous Tense
Must and must not are used with the present perfect continuous tense to show probability of a situation that has happened in the past at the same time as another event. Grammatically, must and must not are followed by the word "have" and then the word "been" and then the -ing form of the verb.

Friend One: Why wasn't Julia at home last night when we stopped by her house.
Friend Two: Her grandmother hasn't been feeling well. She must have been visiting her.

Once again, Friend Two isn't certain. Friend Two doesn't know for certain where Julia was.
Friend One: Why wasn't Vincent at your party last weekend?
Friend Two: He was sneezing a lot Thursday. He must not have been feeling well on Saturday.

Friend Two thinks that Vincent was sick. Vincent may not have been sick but this is the most probable answer.

Quizzes

· Multiple Choice Quiz

· Fill-in-the-Blank Quiz

Created June 14 by Harold Foot

Page Last Updated On June 15, 2005 by Harold Foot