can't (或cannot) but 和can't (或cannot) help but 后面的动词不定式不能带 to ,其中 can't (或cannot) but 很正式,can't (或cannot) help but 在美国英语中尤为常用。如:
One cannot (help) but admire his courage. (= One has to admire ...)人们不禁钦佩他的勇气。(摘自《牛津英语用法指南》413.3)
but 的前面有do 以外的动词时,but 后面的动词不定式 应该带 to。