Functional Order: Fe/Si/Ne/Ti
Dominant Function: Fe
Boromir tends to see himself as an extension of a greater whole, the representative for the nation of Gondor and an extension of all the men of their kind. It offends him that Aragorn would set himself up as in any way morally superior, or would refuse to even consider taking the Ring through Gondor, because it might prove a temptation to mortal men. The idea of writing off everyone in such a manner, and not giving them a chance, is offensive to him, because it contradicts his own experience of the men of Gondor as valiant, brave, and determined. Though a competent soldier easily able to rouse his men to victory and control their outer cities, Boromir is also actively attempting to please his father in every way and hold together the family unit. That his father excludes Faramir and looks down on him for being more of a dreamer than a warrior bothers him, so he tries to include his brother in his victories.
Auxiliary Function: Si
Once within the Fellowship, Boromir focuses on engaging with the hobbits and looking after their best interests. Teaching them how to fight, carrying them through snowstorms, and suggesting they find another route for their physical welfare. He has great respect for the traditions of old…
Tertiary Function: Ne
but also an idealistic lower intuitive belief that yes, the Ring can be used for evil, but it can also be used for good.
Inferior Function: Ti
Others’ refusal to accept or believe this frustrates him, and he spends a great deal of time attempting to convince them to share his point of view (EFJs want an emotional consensus) and give him a chance.
Note: This argument has been taken from Funky MBTI in Fiction.