有一读者问： 在初中英语教学参考书中有这样两个句子：
(1)The scientist does not only know English very well, but also knows Russian and German very well.
(2)The pianist did not only give them a lot of advice, but also played some wonderful pieces for them.
问这里用助动词do是否有误？
按理说，你所举的这两个句子中的not所否定的并不是谓语动词，而是副词only，所以不应该用助动词do而应分别改为：
(3)The scientist not only knows English very well, but also knows Russian and German very well. （此句用词似嫌重复，建议改为The scientist knows not only English but also Russian and German.）
(4)The pianist not only gave them a lot of advice, but also played some wonderful pieces for them.
但实际上，人们并不完全照章办事，而是往往在not only之前加上助动词do，好像not是否定谓语动词似的。所以，例（1）与例（2）用助动词do并没有错。但请注意，在当代英语里，较为常用的结构是例（3）与例（4），例（1）与例（2）似乎较少见了。
顺便说一下，下面not only与but also不对称的句子也是常见的：
(5)He not only plays the piano, but also the violin.
按理说，not only与but also应该对称，后接同样的词类，例（5）应改为：
(6)He plays not only the piano, but also the violin.
我们中国学生固应遵守这条规则。但实际上，诚如一位语法家所说，人们十之有八成会说出甚至写出例（5）那样的句子，因为人们在说not only时，往往并未同时已想好全句的结构。所以，我们不但学习语法规则，更要学习习惯用法。
