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Hi, experts, I need your advise.
What is the difference between when and at which in this case ? Both in this case describe the time, the ealiest date.
Scientist have dated sharp-edged flakes of stone to between 2.52 and 2.6 million years ago, pushing back by more than 150,000 years the earliest date at which humans are known to have made stone tools (Correct)
Scientist have dated sharp-edged flakes of stone to between 2.52 and 2.6 million years ago, pushing back by more than 150,000 years the earliest date when humans are known to have made stone tools (is this wrong?)
An informal definition/general rule of thumb is that "when" emphasizes the period of time in which something occurs and not the time period itself, whereas "at which" refers to the specific point in time, but not necessary the actions occuring in that period.
Remember the time when we went to the store? <- refers to the time when something happens, namely the period when you are at the store, emphasis on the action happening in the tore
The time at which you will go to the store is 9:00pm. <- refers specifically to the time you must go to the store
The second sentence - the earliest date when humans are known - sounds a bit odd
Re: [time] when vs at which
12 May 2009, 16:11