for 有“为期多久”的意思,后面加一段时间,如:I haven't seen you for 3 years.(我有三年没有见到你了.) until 表示“直到什么什么时候为止”,后面加具体时间点,如:we shall be together until death do us part.(我们会永远在一起直到死亡将我们分开)
for后接一段时间,比如two years,three minutes. until后接时间点,比如yesterday, last year.另外,until 后还可以接从句。 We haven't seen each other for 10 years. He didn't see her foreign friend until last year. He won't leave the station until his sister comes.