And和But不能放在句子开头吗？
一些同学在读书的时候英语老师可能教过不能将and以及but等连词放在句子开头，比如不能写：The telephone isn’t working. And that’s not the only problem.
但实际上这一说法是错误的，英语语法和惯用法中并没有规定and以及but这些连词不能放在句首。不少主流写作指南都指出，连词的这一用法是可以接受的。比如the Chicago Manual of Style（芝加哥格式手册）就有这样的说法：
There is a widespread belief—one with no historical or grammatical foundation—that it is an error to begin a sentence with a conjunction such as and, but or so. In fact, a substantial percentage (often as many as 10 percent) of the sentences in first-rate writing begin with conjunctions.
经典写作指南The Elements of Style（风格的要素）一书中也出现过这样的句子：
But since writing is communication, clarity can only be a virtue. And although there is no substitute for merit in writing, clarity comes closest to being one.
那么，为何一些老师会认为and不能出现在句首呢？英国语言学家David Crystal在他的著作The Story of English in 100 Words当中给出了一个解释：在19世纪的时候一些学校老师注意到小孩在写作中容易滥用and这一单词，于是就禁止学生在句子开头使用该词。但这一做法并不科学，正确的方法应该是引导学生用好连词，而不是完全禁止。
英语中像and以及but这样的连词称为并列连词（coordinating conjunction），并列连词还包括for, nor, or, yet, so，人们也因此将这些词统称为FANBOYS (For, And, Nor, But, Or, Yet, So)。这些词都可以出现在句首。
不过并列连词直接放在句首与它们放在句子中间确实存在一些区别，最主要的一点是可以用于强调。比如这两个句子：
(1) Many people fear crashing in an airplane. But riding in a car is actually more dangerous.
(2) Many people fear crashing in an airplane, but riding in a car is actually more dangerous.
第一个句子表意会比第二个句子更加强烈，将But置于句子开头可以强调"riding in a car is actually more dangerous"这一部分的内容。
又比如这两个句子：
(1) Susan wasn’t feeling well. Yet she still attended the meeting.
(2) Susan wasn’t feeling well, yet she still attended the meeting.
第一句将Yet放在句首，这样可以加强语气，让读者将注意力放在“苏珊带病参加会议”这一件事上。
参考资料
https://www.quickanddirtytips.com/articles/can-i-start-a-sentence-with-a-conjunction/
https://www.merriam-webster.com/words-at-play/words-to-not-begin-sentences-with
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