An interesting function of using a superlative + than is that than accepts a comparative object, such as a noun/noun phrase or a wh- interrogative clause the way a preposition normally accepts an object, even though it is NOT a preposition. It can also accept a verb clause, and when it does, that clause is called a comparative subclause.
In a sentence with a superlative + than (this indicates that a comparison is being made), this subclause may be called the hinge element of the comparison. Leech & SvartvikLeech, G. N., & Svartvik, J. (2002). A communicative grammar of English. London: Routledge, Taylor & Francis Group. describes the hinge element as follows:
The hinge element is the phrase that contains the comparative word. The following than-clause modifies the hinge element. It is called a “hinge” because it belongs, in terms of meaning, both to the main clause and to the comparative subclause.(p. 270)
The hinge element can be modified by a nominal relative clause that has been reduced via Whiz-deletionAccording to John Lawler, a Whiz-deletion “is one of the most common and important types of ellipsis in English.” (the complementizer that + to be have both been deleted). It is this reduced structure that is now the comparative phrase (coloured):
*A head-determiner noun phrase (the ones) with an appositive phrase (in the more modern parts of the city): the complementizer (that) + the verb (to be) have both been deleted: the ones [that were] in the more modern parts of the city.
The subordinate clause contains a complementizer (a relative pronoun, such as that, or a wh- interrogative pronoun) that functions as an object that modifies the hinge element:
NOTE: The verbs in each example is transitive. Each proposition implies a question, in that the speaker does not know what what is.
A subordinate clause begins with a subject followed by a verb modifies the hinge element:
SUMMARY/OBSERVATIONS: When superlative + than is followed by a comparative object (noun/noun phrase or a wh- interrogative clause) or a verb clause (comparative subclause), each modifies the hinge element (“the phrase that contains the comparative word,” i.e., more than, less than).
NOTE: While a noun/noun phrase can be an object of than, a comparative subclause, by contrast, must be a verb clause (namely, the wh- interrogative clause or comparative subclause). That a subclause must contain a subject and a verb is reinforced by the fact that the suffix “-clause” appears in the name: a “phrase,” conversely, never contains a subject or a lexical (tensed) verb.