The Big Bang Theory - Back to the Future Grammar

A recent episode of The Big Bang Theory shows Sheldon, Leonard, Raj, and Howard watching Back to the Future, Part II and discussing the appropriate tense to use when talking about something that happened in an alternate past timeline.

There isn't a real tense in English to say "something that would’ve happened in the future of a past that was affected by something from the future," probably because no one has ever encountered such a situation. There's no grammatically correct way to combine tenses in this way.

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