Is there any difference in meaning between the modal verbs in these examples? Do only "may" and "might" express prediction, while "could" expresses that something is not impossible? Is there any difference in meaning between them?

  1. "It could rain tonight."

  2. "It may rain tonight."

  3. "It might rain tonight."

In Betty Schrampfer Azar's "Understanding and Using English Grammar" the degrees of possibilities are expressed by percent. For example, less than 50% certainty is expressed by "might" and "may" and "could". "Where's John?" He could/may/might be at the library." Is there any difference in meaning between them in this example too?


There's no real difference in meaning among those verbs, either in your example or Azar's.

The tone of the speaker's voice would communicate better how certain they think it is than their choice of modal verb.

  • But are there other cases where there is a difference in meaning between modals? For example; "The phone is ringing. Can/could it be Tim?" And in other examples too, "Can/could learning a language be difficult?" "Could/can I take a train here?" Do "Can" and "could" have the same meaning? Jul 27 '21 at 9:14
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    I see a slight difference - 'Can [it] be difficult?' = 'Do some people find it difficult?' / 'Could [it] be difficult?' = 'Is it likely I would find it difficult?'. Jul 27 '21 at 9:36
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    @AntoniaA In most cases, modal verbs have different meanings. It's outside the scope of this site, let alone the comment section, to detail them all
    – gotube
    Jul 28 '21 at 4:23
  • Thank you both very much for your answers. Could you please recommend a book which deals with them in detail? Michael Swan's book is great, but most nuances native speakers taught me on this forum were not mentioned. Jul 28 '21 at 6:40
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    @AntoniaA Swan's Practical English Usage is the best reference book I'm familiar with for grammar nuances. I've never seen one just for modal verbs. Swan does have a series of grammar course books, but I'm not familiar with them
    – gotube
    Jul 28 '21 at 15:17

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