English, as an Indo-European Language, comes from an original language with eight distinct cases: Nominative, Genitive, Dative, Associative-Instrumental, Ablative, Accusative, Locative, and Vocative.
There is a vestige of the "Associative-Instrumental" case in the frozen idiom "the more the merrier." Here, what appears to be the definite article "the" is actually a demonstrative pronoun in the instrumental case: "by the amount more, by that amount merrier".