What is the difference between "The traffic is running smoothly for past 2 hours" and "The traffic is running smoothly for last 2 hours"
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7They are synonyms in this context, meaning "immediately previous". You need to put "the" before "past/last".– fevFeb 4, 2021 at 17:38
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1The meanings overlap, but there is a possible difference. The past two hours would refer to the two hours before now. The last two hours could refer to the two hours before now or (depending on context) the final two hours of an ongoing event.– TaliesinMerlinFeb 4, 2021 at 17:50
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You could redundantly say... for the last past two hours.– user 66974Feb 4, 2021 at 17:50
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2You can also say the two hours past but you can't say *the two hours last. The constructions have grown together but they're still different. Past is still a participle to some degree, but last has passed that boundary.– John LawlerFeb 4, 2021 at 17:59
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@user 66974 But no one does!– WS2Aug 8, 2023 at 11:50
2 Answers
The important thing to note is that the two words are not true synonyms. You could not say, for example, "I was away past week". But you could say "I was away last week".
It is when you refer to a measured period of time with the definite article, such as "the last hour" or "the past hour" as in your examples, that they are interchangeable and mean the same thing.
While there may be no explainable difference between the two, there is a need to be more specific about certain periods of time which could be ambiguous. For example, "last year" generally refers to the last complete calendar year - so if someone said in 2023, "I went on holiday last year", you would imagine they went away during 2022. But "I've been busy this past year" could mean the most recent 12 months rather than a year on the calendar. Likewise with "this past month", it could refer to a period of roughly 4 weeks rather than a calendar month. And "the last hour" could mean the last 60 minutes rather than an hour marked on the clock. In cases like this where we mean to refer to a period marked on the calendar or the clock we tend to avoid either 'the last [x]' or 'the past [x]' altogether.