I am really confused with the following sentences.

• I could do my work earlier.
• I could did my work earlier.


•I would do exercise if I was in your place.
•I would did exercise if I was in your place.

From both, which one is correct? And if both are correct, then what's the difference between them? Please answer timely because I am having the exam of English grammar tomorrow.

  • 1
    We only inflect one element of a "multi-word composite verb" form, and that's already been done with the "auxiliaries" would, could. So any "main" verb must simply be left in the infinitive form do ("unmarked"; we don't include the infinitive marker to). – FumbleFingers Feb 10 '20 at 15:50
  • Did, like all past tense forms (and like all modal auxiliaries), can only occur as the first verb in a verb phrase. Only that first verb can have tense; all following verbs in a verb chain are untensed infinitives or participles. – John Lawler Feb 10 '20 at 17:06


can could shall should will would may might must

are followed by the infintive form of the verb.

The book can be read. "be" is the infinitive form, we do not say "is" or "are" or "was" or "were" here.

I could do my work. "do" is the infinitive form, we do not say "does" or "did" or "done" here.

I could not do the work last week but I can do the work this week.

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