A – General Characteristics of Modal Verbs

Modal verbs such as can / could, may / might, must, shall / should / ought to, will / would have special grammatical properties. They are used together with another verb to express ideas like ability, possibility, obligation, permission, or probability.

Unlike most verbs in English, modal verbs follow specific structural rules. They are always followed by the base form of another verb and do not change according to the subject.

• She can speak three languages.
• They could understand the message.
• He can drive very well.

Modal verbs do not take -s in the third person (not: she cans). They also do not have infinitive forms or participles.

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B – Can and Could: Ability and Possibility

The modal verb can expresses ability or possibility in the present. Its related form could can refer to the past or express conditional possibility.

The complete negative form is cannot, but the contracted form can’t is much more common in everyday speech.

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C – Interrogative Forms

Questions with modal verbs are formed without the auxiliary “do”. The modal verb moves before the subject to form the interrogative structure.

• Can we start writing now?
• Could you wait a couple of minutes, please?
• Can’t you pay more attention?
• Couldn’t you come with me?

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D – Short Answers

Short answers repeat the modal verb used in the question. They avoid repeating the entire sentence.

• “Can you ride a horse?” – “Yes, I can.”
• “Can you swim?” – “No, I can’t.”
• “Could you finish the report?” – “Yes, I could.”

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E – Wh-Questions with Can / Could

Modal verbs can also appear in questions beginning with interrogative words such as what, where, when, why, and how. In these cases, the modal verb follows the question word.

• What can I do for you?
• Where could we find a map?
• How could you be so careless?