I was translating the english to latin exercise 189.
"There will be no danger, if we are (shall have been) careful".
When I noticed my translation was slightly incorrect compared to the key you guys here at textkit wrote. I think my problem lies in understanding the declination of adjective Attent-
Erit non periculum, si attentum fuerimus
Non erit periculum, si attenti fuerimus
I wasn't entirely sure how to decline the adjective as it seemed to have no corresponding noun. I therefore decided it could be used substantively as a noun and rested on the neuter nominative -um.
I've seen adjectives used substantively before, but I can't explain how and why the key declines it as: Attenti ; Except perhaps if it is agreeing with the copula verb fuerimus, which is plural in number; thus declining as nominative plural -i . Although that doesn't explain the assignment of a masculine gender.
Perhaps someone more experienced than me can explain my confusion?