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# [time] when vs at which

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Intern
Joined: 18 Apr 2009
Posts: 8
[time] when vs at which [#permalink]

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25 Apr 2009, 09:31
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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?)

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Senior Manager
Joined: 11 Dec 2008
Posts: 459
Location: United States
GMAT 1: 760 Q49 V44
GPA: 3.9
Re: [time] when vs at which [#permalink]

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12 May 2009, 17:11
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.

e.g.

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

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This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

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Re: [time] when vs at which   [#permalink] 12 May 2009, 17:11
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