In Rivendell, Gandalf was called "Gandalf," (by Frodo, Sam, Elrond, Aragorn, Merry, Pippin, Gloin, etc.), and since, as far as we know, Gandalf and Boromir never really interacted before meeting in Imladris, it seems only logical that he would be called Gandalf.
__________________
...where the instrument of intelligence is added to brute power and evil will, mankind is powerless in its own defence.
|