EED 对介词 by 的释义是: If something happens by a particular time, it happens at or before that time. 对介词 until 的解释是: If something happens until a particular time, it happens before that time... If something does not happen until a particular time, it does not happen before that time and only happens after it. 由此可见, by 1997 和 until 1997 都可理解为 1997 年前。这是不是意味着它们在语义和用法上没有什么区别呢?
虽然介词 by 和介词 until 都表示句子所描述的情景发生在 by 短语和 until 短语所指的时间之前,但是它们所指的具体时间和用法却是不相同的。by twelve o'clock 是指 9 点、10 点、11 点或 12 点,而 until twelve o'clock 则是指 12 点。在用法上,until 用在肯定句中时,要求谓语动词必须是持续动词(be, live, like, love, wait),而 by 却不是这样。因此,下面使用 until 的句子都是错误的(应将 until 改为 by)
You'll have to leave until Monday midday at the latest.
× I will have finished this book until tomorrow.
Until the middle 1960s, the national networks were broadcasting most of their programs in color.
从表意上看, until 表示主句的情景在时间上持续到某个时刻为止。因此, 在肯定句中 until (till) 只能与持续动词连用。而 by 则表示句子的动作发生在某个时刻或某个时刻之前。因此, 它只与瞬时动词 (momentary verbs) 连用。
请对比：
(a) The troops remained there until midnight. 部队在那里一直停留到午夜。
(b) × The troops remained there by midnight.
(a) My girlfriend worked there till Christmas. (CGEL) 我的女朋友一直工作到圣诞节。
(b) × My girlfriend worked there by Christmas.
(a) She arrived by Christmas. (CGEL) 她圣诞节前到达。
(b) × She worked by Christmas.
类例：
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I will have retired by the year 2020. 到 2020 年我将退休。
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I have to keep writing until the end of next year. 我得一直写到明年年底。
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My book will be finished by the end of next year. 我的书明年年底前写完。
[附注]在某些特殊的情况下，by短语也可以与持续动词连用：
By Friday midday, they will have been working on it for seven days. (NCE) 到星期五中午，他们在这个工程上就干了7天了。