Rasha Assem posted:
1) The tea is too hot to drink.
2) The tea is too hot to be drunk.
3) The tea is too hot for us to drink.
I agree with the gist of Ahmed's reply, but I would like to explain to you more precisely why all three sentences are correct.
At a more advanced level than ESL classes typically reach, infinitive phrases such as "to drink" are actually analyzed as clauses. Sometimes they have overt subjects introduced by the complementizer "for" (as in Ahmed's "for anyone to drink"), and sometimes they have understood subjects, as in (1) and (2).
In generative grammar, the infinitive clause in a sentence like (1) is said to have a phonologically null subject (called "PRO"). You can think of this as a different way of describing that the subject is "understood." Sometimes, however, PRO is co-indexed with another noun phrase in the sentence, and other times it isn't.
In the case of (1), PRO is not co-indexed with any other noun phrase in the sentence. In other words, its referent is not overtly present in the sentence. This PRO is sometimes called PROarb. It basically means the same thing as "for anyone" in this case, so my explanation here is still related to Ahmed's.
In sentence (2), however, the subject of the passive infinitival clause "to be drunk" is present in the sentence. Thus, in (2), PRO is co-indexed with another noun phrase, namely, the subject of the matrix clause ("the tea"). We can represent the sentence like this: "The teai is too hot for PROi to be drunk."
Why, then, does (2) have the same meaning as (1)? It is because, in (1), "the tea" is functioning as the understood object of the transitive verb "drink." The basic syntactic structure of sentence (1) may be represented like this: "The teai is too hot for PROarb to drink the teai." (The tea is so hot that no one could drink it.)
When the subject of such a sentence is animate (human or otherwise), there is the possibility of the matrix subject's function as subject or object of the infinitival clause. For example, the sentence "The turkey was too old to eat" is ambiguous. We can't tell whether "the turkey" is subject or object of "to eat."
- Subject: The turkey was too old to eat. Soon it died of starvation.
- Object: The turkey was too old to eat. So they ate a younger turkey instead.
If what I have said here is too advanced for you, forget about it. Just think in terms of implied subjects and objects, and remember that all three of your sentences are correct. All three of your sentences are correct, and (1) and (2) have exactly the same meaning.