愚见: 不是吧。。。assumption是两种情况,一种是logical gap - 作者在文章没有明确说出来需要用它来连接premise 和conclusion的,比如My car is red. Thus, it is pretty. 中间的assumption就是red car is pretty.
另外一种情况就是排除其他的objection,比如I drank coffee last night. thus I did not sleep last night. 选项有可能是coffee would make people stay up all night (和第一种类似)或者 I did not homework that would normally make me stay up all night. 排除它因。