Sense

Base form

Negative

Past tense

Passive

1- Permission

Single word

You may use a pen.

You may not use a pen.

We could use a pen.

A pen may be used.

Phrase

You are allowed to use it.

You are not allowed to use a pen.

We were allowed to use a pen.

A pen is allowed to be used.

2 - Ability

Skills, talents

Single word

I can swim.

I cannot swim.

I could swim.

Novels can be written.

Phrase

I am able to swim.

I am not able to swim.

I was able to swim

Novels are able to be written.

3 - Advice

Suggestion, recommendation

Single word

You should run.

You should not run.

You should have run.

The letter should be mailed.

Phrase

You ought to run.

You ought not to run.

You ought to have run.

The letter ought to be mailed.

3.5 - Serious advice

+ stronger than “should”

Single word

Phrase

You had better take the test.

You had better not miss the test.

You had better go to class.

The test has better be taken.

4 – Necessity – requirement

Single word

You must wear boots.

You must not turn right.

Insurance must be bought.

Phrase

You have to wear boots.

You do not have to go. (choice)

You had to buy insurance.

Insurance has to be bought.

5 – Preferences

(no single word)

Phrase (1)

I prefer to eat at home.

I do not prefer to eat at home.

I preferred to eat at home.

To eat at home is preferred.

Phrase (2)

I would rather eat at home.

I would rather not eat at home.

I would rather have eaten there.

6 – Past custom

When I lived in a dorm…

Single word

I would eat lunch every day.

I would not eat lunch every day

(always past)

Lunch would be eaten.

Phrase

I used to eat lunch every day.

I did not use to eat lunch every day.

(always past)

Lunch used to be eaten.

7 – Inference, educated guess, logical conclusion

Single word

It must be Peter.

It must not be Peter.

It must have been Peter.

My keys must be lost. (pres.)

They must have been lost (past)

Phrase

8 – Expectation

I believe it will happen

Single word

The bus should arrive early.

The bus should not arrive early.

The bus should have arrived.

The letter should be sent. (pres.)

It should have been sent. (past)

Phrase

The bus ought to arrive early

The bus ought not to arrive early.

The bus ought to have arrived.

Polite request

+

-

+ Polite

Would you mind writing?

Wouldn’t you mind writing?

…

Would you like to write?

Wouldn’t you like to write?

…

Would you write?

Wouldn’t you write?

Would it be written?

…

Could you write?

Couldn’t you write?

Could it be written?

- Polite

Do you think you could write?

Don’t you think you could write?

Do you think it could be written?

Informal

Can you write?

Can’t you write?

Can it be written?

Possibility

+

-

+ Probable

It must be raining.

It must not be raining.

It must have rained.

It must be written in Chinese.

It should rain.

It should not rain.

It should have rained. (no rain)

It should be written in Chinese.

It may rain.

It may not rain.

It may have rained.

It may be written in Chinese.

It might rain.

It might not rain.

It could have rained.

It could be written in Chinese.

- Probable

It could rain.

It could not rain.(impossible 100%)

It might have rained.

It might be written in Chinese.