The part of no I don't understand

Watching a French movie the other day--I think it was White, the middle part of Kieslowski's Blue, White and Red trilogy--I was reminded of a question I've had for a long time about French: Why does "pas" mean "no"? This isn't something I was taught when I studied French, but it's hard to miss in contemporary usage. As far as I know, there's nothing in other Romance languages resembling "pas" which has the sense of negation. There's the possibility that it comes from another language group, but it would be weird for that to happen with such an important part of speech.

A little investigation revealed that "pas" was not, in fact, an import.The basic negative form in French, of course, is "S ne V pas". For example., "je ne sais pas," ("I don't know"). The negation "ne" is reinforced by "pas" because the preverbal position doesn't emphasize the negation sufficiently. (The equivalent in English, without the reinforcement, might be something like "I no know"--but we don't say that, of course.)

It turns out that in French "pas" ("step") originally was a noun that matched the verb--something like "I won't go another step." But the specificity of the reinforcer got lost, and for the most part, "pas" came to be used for just about every verb. And eventually, it became the principal signifier of negation. Now, as anybody who watches contemporary French films knows"je sais pas" is commonly used to say "I don't know."

As it happens, this sort of thing isn't a rare occurence in language. It's been observed in many and even has a name: the Jespersen cycle. The fact that the English "I no know" is not considered correct English, is in fact another example of this. The cycle goes like this: over time the normal grammatical negation loses its strength, a reinforcement is added, eventually the reinforcement is perceived to be the negation, and the original negation is dropped. Then the cycle begins all over again.

(I won't get into the English example beyond this: the Jespersen cycle introduced the verb "do" as an obligatory reinforcer, hence "I do not know" => "I don't know".)

Getting back to my question, then: "pas" does not mean "no," per se--at least not in etymological terms. Instead it's a meaning that it's acquired in a pattern that is common in many languages, including English. And I wasn't taught that in school because L'Académie française, the conservative authority in all matters of the French language, has not accepted this linguistic reality. The discontinuous negatives, ne...pas, ne...rien, etc. remain the official form of negation in French.