Student or Learner
I'm having some trouble with grammar and I'm not sure if the sentences below are correct.
She can sing well as I.
He can't run fast as I.
I'd prefer to write it as 'he can't run as fast as I' but someone has pointed out that since we can say 'it is white as snow' it is also possible to write a sentence without 'as' in front of an adjective. I'd appreciate your help on this topic.
You need the first "as" in your two sentences.
"We use as...as... to say that two people or things are equal in some way." --See Swan's Practical English Usage.
Although I can't find a definitive source for you, I do believe there are going to be times when expressions or idioms without the first "as" are possible. For example, "It's good as gold," "It's right as rain," and "She's white as snow" may be fine in informal writing and speech.
See Right as rain - Idiom Definition - UsingEnglish.com for a definition of "right as rain."
Teaching ESL to Adults
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
Isn't true that 'as+adj+as' is used when the main verb of the sentence is positive, & when the verb is negative, 'so' is used instead of 'as' ?
-Fred works as hard as Jane.
-Fred doesn't work so hard as Jane.