How are modal verbs used in English?

Modal verbs are a subgroup of auxiliary verbs. They express modality and thus denote desires, abilities, obligations, or possibilities. Due to their subjective meaning, they are an essential part of the English language and are used very frequently. Since modal verbs can usually only appear in few tenses and not in combination with other modal verbs in a clause, they all have a substitute form, which is then used in such cases. For details about the use of the present tense, take a look at modal verbs in present simple.

Now, compare the following possibilities in terms of appearance in example sentences (an overview can be found under verb forms of modal verbs):

• English modal verbs are commonly employed to express the following characteristics and meanings:
  • can/could:
    • permission:
      • “Can I borrow your car, please?”
    • ability:
      • “I can speak French, but I can’t speak Greek.”
    • possibility:
      • “This can’t be possible.”
    • request:
      • “Could you call me back later?”
    • substitute form or paraphrase with ‘to be able to’:
      • “I’m not sure if I will be able to come to the party.”
      • “Will I be able to borrow your car when I have my driver’s license?”
    • Attention: ‘could’ and ‘to be able to’ have a slight difference in meaning; for details, have a look at this explanation.
  • may/might:
    • possibility or probability:
      • “I might do that later.”
    • politeness:
      • “May I ask you something?”
    • permission:
      • “You may go out until midnight.”
    • substitute form or paraphrase with ‘to be allowed to’:
      • “Mobile phones are not allowed to be used in the meeting room.”
      • “I don’t know if I will be allowed to go to the concert.”
  • must:
    • obligation:
      • “I had an accident, and now I must go to the police.”
    • probability/assumption:
      • “She doesn’t stop reading. That book must be fascinating.”
    • substitute form or paraphrase with ‘to have to’:
      • “Peter had to go home early last night.”
      • “You will have to show your passport at the airport.”
  • must not / may not:
    • prohibition:
      • “You must not smoke in here.”
      • “You may not park in front of the building.”
    • substitute form or paraphrase with ‘not to be allowed to’:
      • “We arrived too late, so we were not allowed to enter anymore.”
      • “You will not be allowed to feed any animals in the park.”
  • need not:
    • a lack of necessity:
      • “You needn’t do that just because of me.”
    • substitute form or paraphrase with ‘not to have to’:
      • “We don’t have to watch the movie till the end.”
      • “They didn’t have to bring any money as they were invited.”
  • will/would:
    • future:
      • “Our trip to Australia will be very expensive.”
    • question/request:
      • “Would you like some coffee?”
    • possibility:
      • “I would stay longer, but I have to go to work.”
    • substitute form or paraphrase with ‘to want to’:
      • “Sam wanted to help you, but he didn’t know how.”
      • “They had always wanted to travel the world, but then they retired and moved to South Africa.”
  • shall/should / ought to:
    • proposal/suggestion:
      • “Shall I turn on the heating?”
    • advice:
      • “You should get some rest; you look tired.”
    • substitute form or paraphrase with ‘to have to’ or ‘to be supposed to’:
      • “Mike was supposed to go to the doctor’s yesterday.”
      • “I had to close the window because Peter had a cold.”

What are the special rules to consider when using modal verbs?

When using modal verbs, the following particularities need to be taken into account:

1. When conjugating modal verbs in the present tense – in contrast to full verbs – an ‘s’ is never suffixed either to the modal verb itself (cans) or to the full verb, even in the third person singular:
   • “Mike can speak a bit Chinese.”
     • not: “Mike cans speak a bit Chinese.”
     • not: “Mike can speaks a bit Chinese.”
   • “You don’t have to walk; my sister will take you to the station.”
     • not: “You don’t have to walk; my sister wills take you to the station.”
     • not: “You don’t have to walk; my sister will takes you to the station.”
2. Likewise, modal verbs cannot convey the progressive aspect (as the present participle or ing-form does):
   • musting
   • willing
3. When specifying the infinitive, ‘to’ is never used with modal verbs:
   • to can
   • to would
4. As modals are also auxiliary verbs, no additional auxiliary verb, such as ‘to do’ or ‘to have’, is used in questions and negations (Do you can …):
   • “Will you be here when I come back?”
     • not: “Do you will be here when I come back?”
   • “Can you tell me the way to the post office?”
     • not: “Do you can tell me the way to the post office?”
5. As mentioned above, modal verbs cannot appear with other modal verbs in the same clause:
   • “If I study hard, I will be able to speak French soon.”
     • not: “If I study hard, I will can speak French soon.”

Further explanations related to ‘Modal verbs’

The following explanations relate to the topic ‘Modal verbs in English’ and may be helpful:

• Use of verbs in English
• What are main/full verbs?
• What is modality?