Sociolinguistic Artifacts

Video explaining Jespersen's Cycle, in which negation in language starts out as [no]+[phrase], becoming [no]+[phrase]+[no], finally becoming [phrase]+[no]. This specific language change has happened or is in the process of happening several times, and it is not entirely clear why. The video goes over what I think is the most interesting theory at 3:10 - negation is semantically important (failing to hear it completely changes the meaning) but usually formally insignificant (it's short and easy to not hear). This leads to speakers innovating redundancy, like in French where "pas" ([no]+[phrase]+"a step") is added, or potentially in English, with "squat" (didn't [phrase] squat).