Modals of necessity - 1

These three verbs are modal verbs:

• must
• have got to
• have to

Modal verbs are auxiliary verbs that express ideas like ability, necessity and prohibition.
Many modal verbs have more than one meaning.
They are always followed by the simple form of a verb (infinitive).

Example: Andrew has to pay his rent every month.
(This shows that Andrew has no choice. He has an obligation to pay his rent. He will be in trouble if he does not pay his rent.)

Let's read about how to express necessity or obligation. The modal verbs “must,” “have to” and “have got to” show that something is not optional; it is necessary.

• Must is the strongest and most serious modal verb of the three and is most common in writing.
  It is unusual to use “must” in questions.
  Example: I must study tonight.
• Have got to is most common in informal speech. It is not used in questions.
  Example: I have got to study tonight. = I must study tonight.
• Have to is the most commonly used modal of obligation. It is useful for forming questions and negatives.

Be careful! The subject and verb must agree for he/she/it subjects AND the question form requires “Do/Does/Did”.