The conductor said we might take the dog along

Permission in the past is expressed by the verbs allow, permit and let:

The teacher allowed us to use dictionaries. He didn't let us enter.

2. May with non-perfect infinitive expresses polite request in interrogative sentences if the subject is the personal pronoun 1^st person:

May I trouble you? May I sit here for a while?

3. May with non-perfect infinitive expresses an offer in interrogative sentences if the subject is the personal pronoun 1^st person:

May I help you?

4. Might with non-perfect infinitive is also used to express suggestions:

We might start right now. There is an earlier train, I’m sure.

5. May with non-perfect infinitive is used to express possibility due to circumstances (absence of obstacles to the action):

It isn't late and he may still come.

The form might is used according to the rule of the sequence of tenses:

I thought he might still come.

6. The form might is used to express hypothetical possibility and the form of the infinitive of the notional verb shows the time reference, i.e. whether it refers to the present or to the past:

If it were not so late he might come.

If it hadn't rained yesterday, we might have gone out of town.

7. The form might is used to express criticism or reproach and disapproval;

a) ‘might + indefinite infinitive’ expresses a request made in the tone of disapproval:

You might help me to carry this bag. Don't you see it's heavy?

b) ‘ might + perfect infinitive ’ expresses reproach for failing to do what was in one’s power:

He might have helped you; he saw that you needed help.

8. Both may and might are used in statements to express the meaning of supposition (speculation) implying doubt or uncertainty. Might means the higher degree of doubt. The form of the infinitive of the notional verb shows the time reference:

He may (might) come in the evening. He usually does.

He might be happy, but he doesn't look it.

9. Phrases ‘ may as well’, ‘ might as well’ are used to show that you will do something you do not really want to do:

I may as well watch TV if there is nothing more to do.

MUST

The modal verb must has only one form that refers to the present. The verbs have to, be to, and be obliged are used to supply the missing forms:

We'll have to look through these papers again. They had to admit the truth. We are to meet tomorrow. She was obliged to do it this way.

The modal verb must has the following meanings:

1. It is used to express obligation, necessity, and duty implying no freedom of choice. In this meaning, it is followed by the indefinite infinitive only:

Children must obey their parents,

The verb have to is more commonly used to express necessity and obligation arising out of circumstances, while must expresses obligation imposed by the speaker:

I have to hurry, or I'll be late.

You must hurry. I'm not going to wait for you forever.

The verb must is replaced by the verb have to in the indirect speech according to the rule of the sequence of tenses:

He said we had to go immediately.

In public notices must expresses an obligation imposed by some authorities:

Passengers must cross the railway line by the footbridge.

The verb must denotes necessity arising out of the nature and consequently inevitable. The same meaning can be also expressed by the verb be to:

Bad seeds must produce bad corn.

The absence of obligation or necessity is expressed by the negative form of the verbs need, have to and have got to: