Because the line of One State is a straight line. The great, divine, precise, wise straight line – the wisest of all
(from Chapter 1, Page 1 of the book, We by Yevgeny Zamyatin: Clarence Brown, 1993 edition)
Is the word ‘wisest’ a noun or adjective in this sentence? It may be an adjective as it is describing the line (and One State, metaphorically). Or a noun, because of the definite article ‘the’ before wisest.
My reasoning for why it can be a noun:
Determiners don’t have to be exactly next to the noun, but they can be. In my example there is clearly lots of determiners but in the subordinate clause of the second sentence… The ‘the’ is modifying ‘wisest'(and hence a noun). If it is treated as a noun then it makes a noun phrase with the ‘the’ being an adjective. The second determiner ‘of’ is modifying the noun ‘lines’ and are not to each other, therefore ‘of’ is solely a determiner and the noun phrase is “all lines”.
The great, divine, precise, wise straight line – the wisest of all
“Wisest” is an adjective functioning as a ‘fused modifier-head’. It’s called this because the single word “wisest” combines, or fuses, the roles of modifier and head, where it heads a noun phrase in a partitive construction. The meaning is “the wisest line of all lines”.