not only...but also通常都是连接两个对称的同类词（组），但偶尔也有不对称的情况。如：

I wish to plead with you to join me in, not only serving humanity, but to also benefit in the process.我想请求你和我一道，不仅是服务人类，但也有利于这一进程。

▲另外，并列连词and, but, or有时也连接不对称的“同类词（组）”。如张道真《英语语法大全》例句：

I feel funny and out of sorts.

I declare this seriously and with confidence.

I devote my spare time to music, books, or playing tennis.