I have a question, I have read this sentence:

the Western powers now yielded when they should have resisted

but I do not understand why they use the present perfect at the end of the sentence 'have resisted' after the auxiliary verb should.

  • 1
    That is not a present perfect. The expression "they should have resisted" uses a non-finite perfect "have resisted", and that "have" is not tensed. The tensed verb is the verb "should".
    – F.E.
    May 17, 2015 at 23:41
  • 3
    Mohammad, please allow at least a day or two before accepting an answer. For info about why this is helpful, see “Not so fast! (When should I accept my answer?)”. This question really deserves an in-depth response.
    – Ben Kovitz
    May 18, 2015 at 2:06

1 Answer 1


Here is the best answer to your question:

We can use 'should have' to talk about past events that did not happen.

  • I should have let her know what was happening but I forgot.
  • He should have sent everybody a reminder by email.
  • They should have remembered that their guests don't eat pork.
  • Good reference. :)
    – LawrenceC
    May 17, 2015 at 22:57

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