Emanuela, I do beleive you are right, but with a BUT! The in + flammare is the break up of the LATIN word and the 'in' is therefore the prefix in Latin, albeit in the 'starting to' or 'into' context. The Latin word thus becomes inflammare and the ENGLISH word inflammable is derived from this word. Whereas, with inobservable, the division is, in = observable and the prefix is an english one.