谁说都有逗号呀?
You use but to introduce something which contrasts with what you have just said, or to introduce something which adds to what you have just said.
`You said you'd stay till tomorrow.'—`I know, Bel, but I think I would rather go back.'...
Place the saucepan over moderate heat until the cider is very hot but not boiling...
He not only wants to be taken seriously as a musician, but as a poet too.
参考资料:collins字典第5版