but 是連詞,連接兩個(gè)并列句,中間用逗號隔開.表示轉(zhuǎn)折
如： I wanted to buy a book, but I don't have enough money.
though 是副詞,但在句中的成分相當(dāng)于連詞.引導(dǎo)從句,不能與but 連用,可以放句首或者句中.意思是盡管
如：Though it is so hot I have to go outside.
I have to go outside though it is so hot.
however 也是副詞,劇中成分相當(dāng)于連詞.可以放在句首或句中,后面一定要用逗號.表轉(zhuǎn)折.放句首時(shí),與前面的句子是轉(zhuǎn)折的連接.放句首時(shí),前后用逗號隔開
如：I wanted to buy a book, however, i do not have enough money.