The structure as…as is used to compare things that are of similar proportion.
In this case the first as acts as an adverb modifying the adjective or adverb that goes after it. The second as can act as a preposition or conjunction. If it is used as a preposition, it will be followed by a noun or pronoun. If it is used as a conjunction, it will be followed by a clause.
Read the sentences given below.
He is as cunning as a fox. (Here the first as in this construction modifies the adjective cunning. The second as modifies the noun fox.)
He drove as fast as he can. (Here the first as modifies the adverb fast and the second as modifies the clause ‘he can’.)
More examples are given below
You can eat as much as you want.
She is as tall as her brother.
He is as good a cook as his wife is! (NOT He is as a good cook as his wife is.)
When we use adjective + noun after the first as, the article should go before the noun.
In negative constructions, we can use not so…as…
She is not so successful as her brother. OR She is not as successful as her brother.
In a more formal style, we use a structure with less than.
She is less successful than her brother.
In English, we use a large number of idiomatic expressions with as…as.
Common examples are given below.
Her hands were as cold as ice.
She is as hard as nails. She will do really well in business.
I didn’t dare to go down to the cellar. It was as black as night down there.
She is as deaf as a post.
Please get here as soon as possible.
These stories are as old as the hills.
Remember that the structure as…as cannot be used to measure things of unequal proportion. In this case, we have to use comparative + than.
She is taller than her brother.