Via @JessZafarris on birdsite, I learned a dark and terrible truth about English's favorite definite article.

See, the 'the' in "the apple doesn't fall far from the tree" is not the same word as the 'the' in "the more the merrier."

THAT word isn't a definite article at all.

Quoting Jess, as she explains that it's even more complex than I first thought...
>>>
þā … þā does mean "when… then"

but it's not what you see in the "the more the merrier."

That word is actually þȳ, the instrumentive case of "that" (þæt), implying utility or causing something to happen. (more people = merrier times)
<<<

þā is a precursor for 'the.'
þȳ is ALSO a precursor for 'the.'
Both words ended up as 'the' in modern English, and apparently NEITHER ONE is the definite article.

I'm still trying to sort this out. I'm not the expert here, but
*sunglasses*
the more I listen to experts, the smarter I get.
*guitar riff*
*explosion of more and merry*

@howardtayler "the more the merrier" encodes that very thing in my head (more = merrier)

What actually made my brain do a mindquake was the "thy kingdom come, thy will be done" line from the lord's prayer. Apparently that was also a when... then... construction originally, but it collapsed into some weirdness in english

@my @howardtayler I would be surprised if that were the case. It is not an if/then in German:

"10Dein Reich soll kommen.
Dein Wille soll geschehen.
Wie er im Himmel geschieht,
so soll er auch auf der Erde Wirklichkeit werden."
https://www.die-bibel.de/bibeln/online-bibeln/lesen/BB/MAT.6/Matth%C3%A4us-6

"Dein" is "thy" in English, the familiar form of "your".