Suppose I know he was ill yesterday. Here are two examples referring to unreality.

  1. He behaved as if he was not ill.
  2. if he had not been ill, we would have had a nice time yesterday.

Why we must use "had done" to refer to past unreality in "if” clause while we don't need in "as if" clause.

1 Answer 1


A past perfect is being used in your second sentence due to the fact that your sentence shows that he was ill before you had a nice time, therefore you did not have a nice time. Otherwise a past tense is used.

  • @DialFrost According to your explanation, suppose I know he was ill yesterday and he behaves less energetic now. Which one is correct? If he (had not been)(was not) ill yesterday, he would be more energetic now. Jun 6, 2022 at 8:04
  • Its "had not been", the event that he was less energetic happened after he was ill @Paddington
    – DialFrost
    Jun 6, 2022 at 8:07
  • @Dannielwang What you say here depends on whether he remains ill today. One could say "Had he not been ill yesterday, he would be more energetic today". But if he remains ill - one might say "If he was not ill, he would be more energetic" - but note my further comment below.
    – WS2
    Jun 7, 2022 at 12:32
  • @DialFrost I have changed my mind about my earlier comment (even though someone did upvote it). The "if" clause clearly is influential here. We do not know - as your answer suggests- that his illness preceded the opportunity to have a nice time. The reason for the use of the past perfect is that an "if clause" requires a tense backshift. Hence when talking about the present one would say "If he was not ill, we would be having a nice time now". The "was" in this instance relates to the present moment.
    – WS2
    Jun 7, 2022 at 12:38
  • @Dannielwang And further to that, your first example, "He behaved as if he was not ill" requires no backshifting - because "as if" is an entirely different "if clause" which means the same thing as "as though". This is not, in my revised view, a correct answer that you have received.
    – WS2
    Jun 7, 2022 at 12:48

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