Full Idea
Number words are not like normal adjectives. For example, number words don't occur in 'is (are)...' contexts except artificially, and they must appear before all other adjectives, and so on.
Gist of Idea
Number words are unusual as adjectives; we don't say 'is five', and numbers always come first
Source
Penelope Maddy (Sets and Numbers [1981], IV)
Book Reference
'Philosophy of Mathematics: anthology', ed/tr. Jacquette,Dale [Blackwell 2002], p.350
A Reaction
[She is citing Benacerraf's arguments]