[ID: youtube comment from Hal Sawyer:
My favorite relic English still used everywhere is the word "the" used in phrases like: "the more I look at this, the stranger it seems, or "the bigger they come, the harder they fall". This "the" is not the article of any noun, it is a different word, a conjunction descended from the old English "þā", pronounced "tha" which means either "when" or "then". Back in early Middle English the structure "if - then" had not taken over and if you wanted to express an if - then relationship you said "þā whatever, þā whatever", meaning "when such-and- such, then such-and-such". "þā" sounds almost the same as "the" and the spelling of the two converged, but the meaning remained totally different. "the more, the merrier" literally means "when more, then merrier" or "if more, then merrier'; same as centuries ago.
update, correction to this:
[image description: tweets from user Matt (official) that read, "this is not quite accurate. this 'the' comes from þȳ, the old instrumental case of the definite article. so it's like 'whereby x, therefore y' or 'by how much x, that's how much y.'
þā ... þā does indeed mean 'when ... then' in Old English, but this temporal correlative is not where we get 'the more the merrier' construction. i'm afraid someone took an OE class and mixed a few things up.
so it doesn't originally mean 'if more, then merrier' as suggested in the comment. it has always meant 'by how much more, that's how much merrier' i.e. double or triple the quantity leads to double or triple the merriment." end id.]
