根据牛津词典的说明，however 可以在句子中作为副词(adv)用，通常有 3 种用法
- 修饰形容词和副词，表示“无论到什么程度，不管多么”。 used with an adjective or adverb to mean “to whatever degree”.
- He wanted to take no risks, however small.
- She has the window open, however cold it is outside.
- However carefully I explained, she still didn’t understand.
- 引导一个从句，表示”不管怎样，无论如何” in whatever way.
- However you love her, she is not going to marry you.
- 连接两个句子，表示转折, “然而；不过；仍然” used to introduce a statement that contrasts with something that has just been said.
- We thought the figures were correct. However, we have now discovered some errors.
分析以上几种情况，其实可以得出如下结论：
1. however 用来修饰(强调)形容词和副词，这时它作为修饰词，和它所修饰(强调)的中心词之间应该是不能间隔开的，或者说，however 和它所修饰(强调)的词必修是连在一起的。当 however 提到句首时，它所修饰(强调)的词也要跟在however 的后面提到句首。however 的这种用法，和 how 是一模一样的， however 本来就是 how 加上 ever 合成的嘛。例如我们说 How beautiful she is， 这个句子， how 修饰(强调) beautiful, 当 how 提到句首，beautiful 也就跟在 how 后面到句首了。
2. however 可以引导一个从句，此时它的含义是“不管怎样，无论如何”。这种情况下，however 是作为它所引导的句子的一个内部成分的，这种情况下，however 实际上可以被认为是修饰它所引导的整个句子的，或者看作是修饰句子中的 verb phrase 的。 例句 However you love her, she is not going to marry you. 这个句子， however 可以被看作是修饰 整个句子 you love her 的，也可以被看作是修饰 love her 这个动词词组的。在这种情况下，however 所引导的从句是一个非独立从句(dependant clause), however 和它所引导的从句之间不可以有逗号(,)或者分号(;)隔离开。
3. however 可以作为一个连接副词，连接两个句子，表示转折关系。这时它所连接的两个句子不存在主从关系。例如 We thought the figures were correct. However, we have now discovered some errors. 这个句子就是这种情况。
注意，当 however这样用的时候，它的位置比较灵活。
- 它可以放在一个句子的最前面，此时，它后面需要一个逗号把它跟它所引导的句子隔离开。例如：We thought the figures were correct. However, we have now discovered some errors.
- 它也可以放在句子的主语后面。例如："I can't make it to lunch. You, however, are going to love that restaurant.”，这种情况下，however 的前后都要有逗号。
- 它还可以放在两个动词之间。例如："I can't make it to lunch. I could, however, join you next week.”，这种情况下，however 的前后都要有逗号。
- 它还可以放在句子的最后。例如："I can't make it to lunch. I could join you next week, however.”，这种情况下，however 的前面要有逗号。
4. 要特别注意 however 的后两种用法在涵义上的区别。比较下列两个句子：
- I am going to go to climb mountains with you however I am busy. 不管我多忙，我都会陪你去爬山。
- I am going to go to climb mountains with you; however, I am busy. 我想陪你去爬山，但是我很忙哎。（所以去不了咯。）