In one of my compositions I wrote the following sentence:
Alla fine, lo scrittore dell'articolo crede che il ministero della salute e l'Alfa devano informare i consumatori.
My teacher considered "devano" a mistake and corrected it by using the second form "debbano". Why is it a mistake although both forms are found in my grammar books?
presente (Congiuntivo)
io deva, debba
tu deva, debba
lui, lei, Lei, egli deva, debba
noi dobbiamo
voi dobbiate
loro, Loro, essi devano, debbano
As an Italian, devano is a rare, old-fashioned form, and I myself had to check whether it was recorded in a dictionary. So, yes, it's technically admissible but nowadays it sounds quite unusual. Presumably, your teacher aims at teaching you contemporary, usual Italian.
As an illustration, here is a graph comparing the occurrences of debbano and devano in Google Books Ngram Viewer corpus from 1800 to 2000:
(Debbano itself appears to be declining: this is possibly due to a general decline in the use of the subjunctive mood in some registers of Italian.)
