by經常是與完成時聯系在一起,具體什么完成時取決于by之后的時間,例如by 2013是過去完成時,by now是現在完成時,by 2015是將來完成時
by＋時間”與動作性強的動詞連用時,主句多用于完成式.by 后的時間可指現在、 過去或將來時間點.如：By the time he was fourteen years old,he had learned maths all by himself.到14歲的時候,他就已經自學了數學[SB 2B p.2].I shall have finished it by the time you come back.你回來以前我就把它做完了[1].By the end of the match,they had kicked two goals and we had kicked four.[JB p91] 比賽結束時,他們踢進了2分我們踢了4分.They must have finished their work by this time.他們現在一定已經完成工作了[2].但是,上述情況中當時間為將來時,主句動作發(fā)生在從句動作之后時,主句動詞可用一般時態(tài).如：If you're not better by then,I'll take you to see the doctor.[JB3 p.85] 如果到那時還不好些,我就帶你去看病.Can you finish this by tomorrow?在明天以前你能做完這件事嗎[1]?間或有用進行式的.如：By the end of the first week the head of the department was saying very nice things about me.第一周末時系主任給我多多美言了幾句 [3].