Modal and semi-modal verbs

Past tense of will

Would

Is used to express advice or regret

Should

To express obligation or certainty

Must

Express the future

Will and shall

May/might express speculation

May and might

Can/Could ability and permission

Can and could

Modal verbs

Meaning: are used to express modalities like obligation, permission, necessity, ability, advice and speculation

Could describe general ability

Could/can't express speculation

May is also used to request or give permission

Shall is only used with I and We

Express expectations

Would also used to make polite requests

To express advice

Ought to and had better

To express ability, particularly on a specific occasion

Be allowed to, be permitted to

Be able to

Have to

Don't have to, don't need to, needn't

Be supposed to

To express a lack of obligation

Express obligations and expectations

To express obligation

To express permission

In the negative form it's weaker than be allowed to

Also used to express regret

Be permitted to is more formal

Semi-modals

These semi-modal verbs don't change their form, they are more like main verbs