I wish I could write English with more freedom than is at present possible.
I am confused about the function of “is” in this sentence. Could you explain the grammar in this sentence?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
The sentence is equivalent to
I wish I could write English with more freedom than the amount of freedom which is at present possible.
Than can be followed by a clause with or without a subject. The implied object of comparison may take different roles in that clause:
There was more food than I wanted. (object of "I wanted")
It seems that there were faults in more places than we looked. (prepositional phrase, even though the preposition "in" is in the matrix clause, not the complement clause)
When the implied object is the subject of the clause, it is usually omitted, as in your example.
Another possibility is "than that which is at present possible": people might write that, but hardly anybody would say it.
Grammatically, it means that than can take a predicate: a clause