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I am trying to understand the grammar of the first sentence. Only the first sentence is correct but I don't understand why the other sentences are not.

  1. "If he didn't say "Hello", he couldn't have seen you".

  2. "If he didn't say "Hello", he couldn't see you."

  3. "If he hadn't said "Hello", he couldn't have seen you."

  4. "If he hadn't said "Hello", he couldn't see you."

I used the construction in 3 because in Michael Swan's "Practical English Usage" I read "we use "could have.. to talk about unrealised past ability or opportunities-to say that somebody was able to do something, but didn't do it, or that something was possible , but didn't happen. But in my sentences both actions happened. The person did say "hello" and the other person saw him/her. So it's not what Michael Swan is talking about in "I could have won the race if I hadn't fallen." Is this why only the first sentence is correct? I found a similar construction in the book's another example "I couldn't have won, so I didn't go in for the race." According to Swan negative sentences suggest that somebody would not have been able to do something even if they have wanted or tried. Butit isn't the same as my first sentence, is it? It also gives this example, "I could have won the race if I hadn't fallen." The construction is the same as my third sentence but the meaning is different.

Antonia A
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    I think they probably all mean different things. For example, #1 implies he *didn't* greet (because he didn't see), whereas #3 implies he both saw and greeted. It's a bit harder to imagine suitable contexts for #2 and #4, but #2 might be used to imply we're talking about his habitual interactions in the past, and #4 could be referring to one specific act of greeting in the past, which "explains" why it's possible for him to see you *now*. – FumbleFingers Jun 08 '21 at 18:10
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    Unless I'm much mistaken, exactly the same combinations of verb forms and meanings would apply with simple intransitive verbs. So it might be easier to think things through with, say, If I didn't ask / hadn't asked, I wouldn't know / have known**. – FumbleFingers Jun 08 '21 at 18:15
  • Thank you so much. Thus neither is wrong. But in Swan's examples can "didn't" be used instead of the past perfect and "can" instead of "could"? "I could win the race if I didn't fall." "I couldn't win so I didn't go in for the race." Or is this structure could have done with the past simple is only used when somebody would not have been abe to do something even if he had wanted or tried to? But with conditional sentences "I could have won the race if I hadn't fallen" can I use didn't instead of "hadn't" and "could" instead of "could have"? – Antonia A Jun 09 '21 at 05:21
  • Swan: "I couldn't have won, so I didn't go in for the race." My question sentence: "I couldn't win so I didn't go in for the race." – Antonia A Jun 09 '21 at 05:24
  • Swan: "I could have won the race if I hadn't fallen." My question: "I could win the race if I didn't fall." – Antonia A Jun 09 '21 at 05:25
  • Can the structure you mentioned be used in either : "So it might be easier to think things through with, say, If I didn't ask / hadn't asked, I wouldn't know / have known". – Antonia A Jun 09 '21 at 05:26
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    First pair - Swan: "I couldn't have won, so I didn't go in for the race", You: "I couldn't win so I didn't go in for the race." To me, those are both fine, and mean the same. Te second pair are different. Swan: "I could have won the race if I hadn't fallen" implies I did fall, and thus didn't win. But your "I could win the race if I didn't fall" implies a "narrative reference time" in the past (during or before the race) at which time it wasn't yet known whether I won or not - but at that time I knew I could win, so long as I didn't fall. – FumbleFingers Jun 09 '21 at 10:44
  • Thank you!!! Do these mean the same : "If I didn't ask / hadn't asked, I wouldn't know / have known? Is "didn't ask and I wouldn't know" mixed conditional and is it used instead of third conditional "hadn't asked and wouldn't have known?" – Antonia A Jun 09 '21 at 11:28
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    If I didn't ask I wouldn't know is a *generic / general "truth"* assertion (same as If God did not exist, we would have to invent him - which imply without categorically asserting that I did/will ask, and God did/does exist). As a learner, you should probably forget about If I didn't ask I wouldn't have known (it's "valid", but too complicated and unusual to dissect here). If I hadn't asked I wouldn't have known categorically entails both facts - I *did* in fact ask, and therefore I definitely *did / do know*. – FumbleFingers Jun 09 '21 at 13:08
  • Thank you so much!!! :) – Antonia A Jun 09 '21 at 15:38

1 Answers1

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"He couldn't have seen you" here doesn't mean "he wasn't able to see you" but "I'm sure he didn't see you".

The order of events is: He didn't see you, and so he didn't say "Hello".

At first I don't know whether he saw you, but you tell me that he didn't say "Hello" to you. Because I know he's generally a polite person, I'm convinced that if he had seen you, he would have said "Hello".

So I conclude: If he didn't say "Hello", it means he didn't see you.

Or in other words: If he didn't say "Hello", he couldn't have seen you.

Divizna
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