Modal Verbs of Deduction

modal verbs

Modal verbs are a category of verbs and modal verbs for deduction is a subcategory. Here are all the modals:

I must go now.
I should go now.
I may go now.
I might go now.
I can go now.
I will go now.
I shall go now.

Preposition “to”

Note that there is no “to” between verbs. Compare these phrases:

I want to go.
I must go.

“Want” is not strictly speaking a modal because it takes “to”.

Many Functions

Modal verbs have many functions. If you try to study all the verbs together, it will be confusing. The best way to learn vocabulary (including modals) is in context. Look for a real situation. In this lesson, we will analyse several situations.

Deduct versus Deduce – two different verbs

The word deduction is a noun which has two important nuances. One is the verb “deduce” and the other one is the verb “deduct”.

Deduct means to subtract. Look at the four common mathematical operations:

Subtraction (deduction)

Zero Conditional

If you deduct four from sixty-five, you get sixty-one.


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The Other Meaning of Deduction – to deduce

The other meaning of deduction is the meaning in “deduce”. It means to “infer” or “guess” or “think”.


The best way to understand language is to look at the situation which it is used in. Here is a situation:

You sent a friend to stay in a room with your uncle in London but you have not heard from him and you ring to ask if it is ok, but his wife answers. The question is:

Is that room ok?

Present Deduction

That room is ok
That room must be ok
That room might be ok
That room could be ok
That room may be ok

The first one “will” is one hundred per cent certain. The second one “must” is about ninety per cent. The other three “may”, “might” and “could” are less certain, about thirty per cent.

Future Deduction

Here is a situation for future deduction. You sent a job application without original documents. You used copies. You ring to ask the HR manager if it will be ok.

Your question is:

Will that be ok?


That will be ok
That should be ok
That might be ok
That may be ok
That could be ok

The first one “must” is a hundred per cent certain. “Should” is ninety per cent. The other three, “might”, “must” and “could” are less certain, perhaps thirty per cent.

Past Deduction

You ask the advertising manager if the report you submitted was long enough. He gives one of the following answers:

That was long enough.
That must have been long enough.
That could have been long enough.
That might have been long enough.
That may have been long enough.

The first one is certain. The second one is ninety per cent certain. The remaining three are about thirty per cent certain.

He must be in Italy by now
He should be in Italy by now
He may might could be in Italy by now

That should have been ok is an expression of past regret
That should be ok can be an expression of present regret or complaint

It must be 430
It might could may be 430

It should be ok

Link to More Lessons

Verbs – an overview of the tenses

Three Common Ways to Express the Future

Link to Academic Vocabulary Lesson

Deduction – Deduce – Deduct

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