Which is correct and what is the difference between:"When they used the system they have succeeded"AND"When they used the system they had succeeded"
You're mixing your tenses incorrecty. The first verb in each is in simple past tense. In the first sentence, you have the past and the present perfect. The second has the past and past perfect. It is permissible to mix tenses in some instances, but it doesn't fit here. Simple past tense for both works best, and present perfect could be used too . You need a comma after 'succeeded'.
When they used the system, they succeeded
When they have used the system, they have succeeded.
|link comment||answered Aug 27 '13 at 00:50 Lewis Neidhardt Grammarly Fellow|
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