French author says that Italian and French do not come from Latin

I just noticed a link to this blog on Interlng an hour or so ago. It's a French author named Yves Cortez who has published a book called “Le français ne vient pas du latin” ("French doesn't come from Latin") on his view that Latin did not diverge into the Romance languages of today, but that rather the Romans wrote in Latin but spoke in Italian, and that Italian is actually a separate branch of the Indo-European spectrum, and thus not diverging from Latin but always existed alongside it.

The blog is in French but there is an English page here explaining the book's premise:

However linguists, who are aware of substantial divergences between Latin and the Romance languages both in terms of syntax and glossary, have taken a first step towards supporting a different theory. They had to appeal to the concept of “Vulgar Latin”, which is supposed to be the spoken language resulting from Classical Latin. It is the former that is purported to have given rise to the Romance languages.

I agree with these linguists on one single point, namely that Classical Latin could not have evolved into the Romance languages, but I disagree on the rest:

- What we wrongly call “Vulgar Latin” is none other than Italian

- This Italian did not develop from Latin, but is a distinct Indo-European language

- So the Romans were bilingual, speaking Italian and writing Latin

- The Romans gave their Empire two languages: a spoken language which was Italian and a written one, Latin

I see there's also a fairly long thread here about his view on the origin of the words "guerre" and "guerra".