however,yet这两个词都含 “而、然而、却” 等转折的意思。
however:“然而、可是” 语气较弱, 联接也较少松弛。 因此常被用来插人句子中间。
例如:
You ask me to do the work I am afraid however that I amnot equal to it. “你请我做这事,然而,我恐怕不能胜任。”
yet:“而、然而、可是”,正式用语,让步转折的语气较强烈,而且多指付出了努力,却与预期结果或主观打算相违背。常用短语:and yet 然而、可是:but yet 但是还…… 
如:His speech was almost unintellgible , ( and ) yet for some unknown reason I enjoyed it very much. “他的演讲虽有些莫名其妙,但不知为何我却非常愿意 (喜欢) 听。”
yet(用于疑问句和否定句)
还,尚,仍
如:He has not come yet.
他还没有来.
She is yet a child.
她还是个孩子.
He was poor,yet happy.
他很穷,可是很快乐.
The driver's not yet conscious after the accident.
驾驶员在出事后,还没有苏醒过来.
The doctors have not yet decided how the woman died.
医生们尚未确定这位妇女的死因.
however
然而,但是
adv.无论如何,可是,仍然,究竟
conj.不管用何种方法,然而,可是
however 更像是“然而”yet比较长用来表达“但是”其实没有什么区别的除了however是比较长用在写作方面,yet比较长用在对话沟通方面。