by 引起的时间状语表示了动作的截止点，其意思为"不迟于某一时刻将工作做完"，所以主句一般是完成时态。当然可以有将来时态，如：I'll be there by five o'clock.而till则表达其一动作一直持续到某一时刻，但句中的动词一定要用持续性动词，而瞬间的截止性动词应用其否定句式，如：I won't finish this work till(until) next weekend.
［误］ Till the end of next week. I will have finished this work.
［正］ By the end of next week. I will have finished this work.
［析］ by 引起的时间状语表示了动作的截止点，其意思为"不迟于某一时刻将工作做完"，所以主句一般是完成时态。当然可以有将来时态，如：I'll be there by five o'clock.而till则表达其一动作一直持续到某一时刻，但句中的动词一定要用持续性动词，而瞬间的截止性动词应用其否定句式，如：I won't finish this work till(until) next weekend.
