[1.] "If I would have known about the party, I would have gone to it."

This is INCORRECT, although commonly used, especially in American English.

The correct form is: [2.] If + had + past participle, would + have + past participle

[For the above example:] [3.] "If I had known about the party, I would have gone." This is CORRECT.

I accept that [2] is correct, but exactly how and why is 1 wrong? I've never heard it before, because this is an argument from personal experience, which can be a fallacy. If the apodosis is a 3rd cdtl (abbreviation for 'conditional'), why must the protasis also NOT be a 3rd cdtl?

  • I can't get past Karen's "issues" about grammatical forms that she finds "annoying."
    – user6951
    Nov 5, 2014 at 16:40
  • This is a bit advanced for people who're still learning English. It should be moved to ELU
    – Carl Smith
    Nov 5, 2014 at 16:43
  • 2
    No, it shouldn't. ELL is the perfect place to talk about conditional constructions, something that's challenging for L2 speakers but automatic for L1 speakers.
    – user230
    Nov 5, 2014 at 17:07
  • @CarlSmith If you follow the conditional-constructions tag you will see that questions about this arise constantly here. Nov 5, 2014 at 18:01
  • 1
    “Third conditional”, among those who use the term (mostly teachers of English as a second language) is not a morphological term but a syntactic term. That is, it does not designate a particular form or construction of a verb but a particular sort of IF...(THEN) construction (conditional construction) in which both the IF clause (condition clause, protasis) and the THEN clause (consequence clause, apodosis) employ verbs cast in a form which signifies past tense and irrealis or ‘hypothetical’ mode. Nov 5, 2014 at 18:29

1 Answer 1


What is correct or not in case such as this is largely a convention. In British English, If I would have known you were coming, I would have baked a cake is considered incorrect both because prescriptive writers tell we have to say If I had known and because descriptive writers confirm that that is what we do say in standard BrE (but see the note at the end of this answer).

I don't know what the 'rule' is in American English, but I know from contact with Americans over the last fifteen years that many of them say If I would have known .... Discussion with trainee teachers suggests that many of them believe it is correct.

Note. In British English,

Instead of an ordinary preterite perfect, a non-standard 'double perfect' is often found:

If it had've come yesterday he would surely have told her.

I wish he hadn't've left.

This is largely restricted to speech (or the written representation of speech) It appears to be increasing in frequency and though it is not yet established as a standard form, it is used by many who in general speak standard English

Huddleston & Pullum, 2002.151, The Cambridge Grammar of the English Language

In contracted forms such as If I'd've known ..., one cannot say for certain whether the 'd is a contraction of had or would. However, most British speakers who use this form expand the 'd to had in emphatic and negative utterance.

  • I've gone in to separate out your examples onto different lines. You could either roll back the edit or widdle around with a full stop and my ugly square thingy and name will disappear, as I'm sure you know! Nov 5, 2014 at 21:22

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