在意思上它们是不一样的,在否定句中既可以用not as ...as...也可以用not so...as,而在肯定句中只能用as...as.．．
He is as clever as you.(He is not as/so clever as you.)
但下面的句子要特别注意：
1) I'll come back as soon as possible.
2) The clouds are as white as snow.
3) He is so strong as to lift a big stone.(so...as to do:那么．．．．．．以至．．．．．．）