- Don't buy more books than are necessary.
- Don't buy more books than necessary.
- We have three more doctors than are necessary.
- We have three more doctors than necessary.
What is the difference between the two constructions?
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Sign up to join this communityBoth structures are correct but, for the past fify years, "more than necessary" has come to be used more often than "more than is/are necessary". See Ngram below.
Both forms are grammatical, there being no need for the verb 'is' or 'are'.
I guess, it is the form of 'ellipsis' which omits the subject of the following clause, so it's used as 'than is necessary' rather than 'than it is necessary'. ...than (it) is necessary.