It's not a silly question. These forums (fora?) are full of reports by people who booked two seats for this reason, only to find that they were assigned seats across an aisle from each other or separated by a fixed armrest. Watch out for exit rows that way: they often have tray tables in the armrest, because the next row forward is too far away or to prevent a tray table from obstructing the exit, so their armrests don't raise out of the way. (Seatguru.com would have details for specific seats and aircraft types.)