however = 但是 但為什麼它不是 連接詞 而是adv

However是個助動詞(adverb), 亦是個連接詞(conjunction).
助動詞可用作形容動詞(verb), 形容詞(adjective)或另一個助動詞(adverb).
先不要說however這個字,你先看我下列淺句便會明白助動詞是怎樣用的了：
1) He finished his homework quickly.
助動詞quickly就用以形容動詞finished了.
2) These flowers are very pretty.
助動詞very 就用以形容形容詞pretty了.
3) She can dance quite beautifully.
助動詞quite就用以形容另一助動詞beautifully了.
however 怎去形容形動詞呢? 請看以下例句：
(1) However you like her, she doesn't like you.
助動詞However 就用以形容動詞like了
(2) However he looks at it, it is going to be very expensive.
助動詞However 就用以形容動詞looks了
however 怎做連接詞呢? 請看以下例句：
1) She shouted at her younger brother loudly, however, she meant to
teach him to behave himself.
你說得對, 正如我上述所講, adverb除了用以形容動詞,還可以形容形容詞及另一個adverb.但請留意並非每個助動詞adverb也可用作連接詞。
你最後的問題答案是however和助動詞有關係的,如上述(1)(2)例句,however
本身就可用作助動詞adverb了。

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However解作「但是」、「不過」時，當然是連接詞，能說說哪處說這個用法不是當連接詞用？

However is an adverb of concession It is not like an ordinary adverb which is used to describe/ modify a verb. It is used as a connective, to state that the idea stated in the second sentence is not the same as that in the first one. It is used to link two ideas together. It is a connective or an adverbial.