1. good 只用作形容词，不用作副词，其副词形式用 well。如：
He speaks good English. 他的说得好。
He speaks English well. 他的英语说得好。
2. well 既可用作副词，也可用作形容词。用作形容词时，其用法很有限，只表示“的”“恰当的”或“令人满意的”等。如：
She is very well. 她身体很好。
Things are well with us. 我们事事如意。
注：一般说来，well 用作形容词时，只用作表语而不用作定语(如上例)，但在美国英语中，well 表示“身体健康”时有时也可用作定语。
二、从相关短语用法上比较
be good at 与 do well in：两者均可表示“擅长”。如：
He is good at languages. 他擅长学语言。
She is good at telling stories. 她擅于讲故事。
They all did very well in the examination. 他们这次都考得很不错。
注：表示擅长某一学科时，也可用be good in。如：
He is good at [in] maths. 他擅长。
2. as good as 与 as well as：用于本义时，两者均可表示“与……一样好”，但 good 是形容词，而 well 是副词。如：
他说英语说得跟她一样好。
正：He speaks English as well as her.
正：His English is as good as hers.
但是，用于引申义时，两者的意思很不相同：as good as 意为“几乎”“差不多”(=almost)，as well as 意为“而且”。如：
The work is as good as finished. 差不多干完了。
He as good as said I’m a liar. 他无异于说我撒谎。
She’s clever as well as beautiful. 她不但漂亮，而且。
As well as breaking his leg, he hurt his arm. 他不但摔断了腿, 而且还伤了胳膊。
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