英语列举时，and前面要不要加逗号？
She has been to France, Italy and Spain.
这句话的标点对吗？and前面要加逗号（comma）吗？
这就是今天的话题了。这个用在and和or前面、有三者及以上并列时的逗号叫做serial comma，或者series comma、 Oxford comma、Harvard comma。
基本原则
简单来说，加不加这个逗号，主要是习惯和地域问题。绝大部分的美国出版写作规范（style）都会要求加上这个逗号；而大部分的英国出版写作规范则反对使用serial comma或者认为它可有可无。对于个人日常写作来说，那就更多地取决于习惯了，无关对错。
凡事总有例外
然而，有的时候，如果不加这个逗号，可能会出现歧义。比如：
The interviewees(被采访者) were his two ex-wives(前妻), Mary and Anna.
请听题：被采访者一共有几个人？
这个问题在于，Mary and Anna到底是他的ex-wives（同位语），还是与“ex-wives”并列的另外两个被采访者？
这时候加上serial comma就可以避免被理解Mary and Anna为同位语了：
The interviewees were his two ex-wives, Mary, and Anna.
（被采访者是他的两个前妻、玛丽和安娜）（一共四人）。
当然也有其他的处理方法，比如调换语序：
The interviewees were Mary, Anna and his two ex-wives.
当然，如果确实只采访了他的两个前妻的话，那就应该改成：
The interviewees were Mary and Anna, his two ex-wives. （注意只有两者并列时，and/or前不能加逗号）
美国缅因州曾经还有过一个案子，因为法律条文里缺少serial comma导致歧义。（这个例子比较难，英语一般的朋友可以跳过）
法律原文说对特定货物的以下活动中，货运公司不需要支付加班费：
canning, ... , storing, packing for shipment or distribution(经销/送货给零售商)。
请问：货车司机进行distribution能不能拿到加班费？
货车司机：当然能啊，原文说的免加班费活动是：packing for [shipment or distribution]，只有打包（packing）是没加班费的。而且distribution用的是名词，前面列的canning、storing、packing都是动名词，明显不是和它们并列的。
公司：当然不用付啊，原文说的是：[packing for shipment] or [distribution]，运送给零售商（distribution）也没加班费。shipment和distribution不是一回事吗，怎么可能写两遍。
最后法院根据当地规定，如果有歧义，那么按保护弱势群体一方理解，所以认定公司需要支付加班费。不过后来这一条法律被修改成了“canning; ... storing; packing for shipment; or distributing”。
有人可能想说，既然serial comma能避免歧义，那我每次都加上不就好了？别高兴太早！看下面这个例子：
She went to China with her mother, Mary, and John.
请问：她跟几个人一起去了中国？
是和她名为Mary的母亲（同位语）以及John两个人，还是她母亲、Mary和John三个人？
这个时候去掉serial comma反而能避免歧义：
She went to China with her mother, Mary and John.
（她同她的母亲、玛丽和约翰一起去了中国。）（一共三人）
或者调换顺序：
She went to China with Mary, John and her mother.
如果确实是和母亲与John两个人一起去的话，那就是：
She went to China with John and Mary, her mother.
更尴尬的情况是，有的时候，不管加不加serial comma，都会产生歧义，比如：
They went to China with Betty, a maid and a cook.
They went to China with Betty, a maid, and a cook.
老问题：到底是和几个人一起去的？换句话说，Betty是单独的一个人，还是他们的女仆，还是他们的女仆兼厨师？
这种情况下只能想别的办法了，比如：
一个人（Betty是女仆兼厨师）：
They went to China with Betty, who was a maid and a cook.
They went to China with Betty, both a maid and a cook.
They went to China with Betty (a maid and cook).
They went to China with Betty, their maid and cook.
两个人（Betty是女仆，还有一个厨师）：
They went to China with Betty (a maid) and a cook.
They went to China with Betty – a maid – and a cook.
They went to China with Betty, a maid, and with a cook.
They went to China with the maid Betty and a cook.
They went to China with a cook and Betty, a maid.
三个人（Betty是女仆兼厨师）：
They went to China with Betty, as well as a maid and a cook.
They went to China with Betty and a maid and a cook.
They went to China with Betty, one maid and a cook.
They went to China with a maid, a cook, and Betty.
They went with Betty to China with a maid and a cook.
如果对你有所帮助，请你点个赞，谢谢(づ￣ 3￣)づ
参考资料：
Serial comma. (n.d.). Retrieved March 21, 2020 from Wikipedia: https://en.wikipedia.org//wiki/Serial_comma
