4
Google gives you 0 results so I'm a bit skeptic.
Example sentence:
Speaker A: "My husband has never lied to me."
Speaker B: “You wouldn’t know if he did.”
(Meaning that Speaker A wouldn't know her husband was lying even if he lied to her. Because he wouldn't have told her.)
4Yes, it's fine. The complement of the auxiliary verb "did" is ellipted, but understood as "Lie to you". This is perfectly normal in such constructions – BillJ – 2017-03-24T15:19:26.667
2The two alternatives are *You wouldn't know if he did [lie to you at any time in the past, present, or future]* and *You wouldn't know if he had [lied to you in the past]*. Which in principle do mean slightly different things. – FumbleFingers Reinstate Monica – 2017-03-24T15:48:31.820
There are trillions upon trillions of possible English sentences, and it is easy to make a new one that no one has ever spoken before, so it's not surprising that you can't find any results for one particular sentence. – stangdon – 2017-03-24T16:51:59.833
@stangdon Yes, but I for one am very surprised indeed. The sentence only involves function words (auxiliaries and pronouns) apart from the verb know. It's like getting no results for "He didn't know it". – Araucaria - Not here any more. – 2017-03-24T16:57:26.727
Try instead googling "you would know if you did". 2.5 million results. – Andrew – 2017-03-24T21:19:38.947
How about "You wouldn't know it if he did"? In this sentence, I take "if he did" to be the direct object of "You wouldn't know," anticipated by dummy "it." The original sentence without "it" could sound like a conditional, which it is not. – Gustavson – 2017-03-25T02:12:43.463
It's very common and you can find plenty of attestations. For example, https://books.google.com/books?id=w1y9cXLrkyQC&pg=PA58&dq=%22not+know+if+he+did%22&hl=en&sa=X&ved=0ahUKEwik0vv6mPLSAhUE44MKHfi3AfYQ6AEILzAD#v=onepage&q=%22not%20know%20if%20he%20did%22&f=false
– Tᴚoɯɐuo – 2017-03-25T17:38:04.057