Sometime around the 7th century, a grammarian got fed up and started collecting all the annoying mistakes that people kept making in Latin. He wrote them up in the Appendix Probi, a straightforward list of the “say this, not that” variety. The most interesting thing about the Appendix Probi is not that it shows that people have always been making usage errors, but that the errors people made in Latin show the specific ways that Latin turned into its descendants, the Romance languages, including Spanish, French, and Italian.

1. FEBRUARIUS NON FEBRARIUS

The advice in the Appendix is not so different from what you might see on the same kind of lists for English today. Where our lists warn us to use “dependent not dependant” and “February not Febuary,” the Appendix tells the Late Antiquity Era Latin user that it’s “aquaeductus non aquiductus” and “Februarius non Febrarius.” Despite that advice, the syllable that Latin speakers kept leaving out of Februarius stayed left out in what eventually became Spanish (Febrero), French (Février), and Italian (Febbraio).

2. AURIS NON ORICLA

In many places where Latin had a diphthong vowel /au/, the descendant languages have /o/. For example, in Spanish, Latin paucus (a little) became poco, causa (cause) became cosa (thing), and taurus (bull) became toro.

You can see evidence of this change beginning in the Appendix Probi when the author complains that is should be auris (ear), not oricla. People were already swapping out /au/ for /o/, and that continued to the point where the word for ear in Romance languages became oreja in Spanish, orecchia in Italian, and oreille in French.

3. CALIDA NON CALDA

Another change from Latin to the Romance languages was the loss of unstressed vowels in the middle of a word. The Appendix says it should be “calida non calda,” and “viridis non virdis.” These days the words for warm and for green in Italian (calda, verde) and French (chaud, vert) are still missing that internal extra syllable.

4. EXEQUIAE NON EXECIAE

Some widespread changes in Latin’s descendants, like the change from a /kw/ to a /k/ sound, make frequent appearances on the list, (exequiae non execiae, equs non ecus, coqus non cocus, coquens non cocens, coqui non coci) even when they don’t address specific surviving words that changed. There’s no complaint about quomodo (how) becoming comodo, but that’s what happened when it turned into como (Spanish) and comment (French) in the descendant languages. The Appendix is evidence that that particular sound change was already well underway.

5. TABULA NON TABLA

Many of the annoying mistakes in the list nearly directly represent current-day correct words. Some exactly represent them. The advice that the word for crowd should be “turma non torma” is perfectly ignored by the fact that the Italian word for crowd turned out to be torma. The complaint about tabla for tabula is perfectly ignored by the Spanish word for board, tabla. With a few additional changes, that same mistake reaches all the way into English (through French borrowing) with table. Centuries of language change between late Latin and modern languages mean that mistakes have been piled upon mistakes. That, essentially, is what modern languages are. Really, it’s what all languages are. The same will be true for your descendants, though by then, they may be descendents.