Agreed that logic isn't a branch of mathematics (even today, my experience has been that logic classes tend to be offered by philosophy departments, not math). My only quibble was the implication that logic is somehow much newer than mathematics (/Euclid). It's not like people suddenly woke up one day in the 20th century and thought for the first time: "huh, I wonder what separates correct arguments from incorrect ones?" But point taken that Aristotle was not as formalist in his time.

If you have some sources to read more about this:

> I get the impression that a lot of more traditional philosophers of logic hated the formal turn.

I would be very interested! (Don't doubt it at all, just sounds like an interesting period I don't know as much about as I'd like.)