Dominant Te: Mycroft is all about order and organization. He evidently “is the British government” and has a large compendium of people to whom he delegates tasks. His plans tend to be expansive, detailed and always quickly put into action. He hates it when Sherlock’s snooping interfere with any of the long-term plans he’s put into place and comes to his apartment directly tell him to stop. He likes to be in control of everything, and that often includes taking charge of his brother’s life as well (much to Sherlock’s loathing). Mycroft dislikes his emotions and seems almost to take pride in dismissing “sentiment.” He pretendsnot to love, even when it comes to family. Mycroft doesn’t only feel the need to organize the world, but feels the same compulsion toward his environment –enough so that Sherlock deliberately messes things up just to annoy his “OCD” side.
Auxiliary Si: Mycroft is continually looking at the past and even has a difficult time recognizing when Sherlock has changed so that when he looks a Sherlock, he sees him as the same frightened little boy that he saw growing up. In general, Mycroft prefers to observe tradition, and as a result, he has an extremely difficult time understanding his brother’s radical behavior. Mycroft is much more of a traditional than Sherlock is, and he tends to view Sherlock’s non-conformity as childishness. Mycroft doesn’t want his parents to refer to him by nick-names, but somewhat rudely asks his mother to “struggle all the way to the end” of his name.
Tertiary Ne: Mycroft isn’t particularly intuitive, and when he isn’t observing logical evidence, he tends to come to incorrect assumptions about people –thus, ease understanding John and complete inability to understand Sherlock. Though he’s known Sherlock for years, admits that he still finds him unpredictable. With this in mind, he plans for anything, making sure to have all his exits covered in case of disaster. Mycroft finds Sherlock’s games childish because he would rather devote his time to more serious endeavors. Mycroft is always viewing everything in terms of the big-picture, and is often frustrated when Sherlock deviates to follow a trail of details.
Inferior Fi: Mycroft likes to pretend that he isn’t emotionally attached to Sherlock, yet through his actions we see that this isn’t the case at all. He feels the need to monitor and protect him, but does so in a controlling sort of way, such that Sherlock shuts him out. Mycroft is good at hiding his emotions, to the point that takes a drugged drink of punch to get him to openly share his feelings with Sherlock. He doesn’t think that he needs other people in his life (insisting that he’s not lonely). His work is primarily aimed at benefiting the world at large, but he often places more importance on this work than he does trying to secure a true relationship with his brother.
Most people seem to see Mycroft as either an INTP, ISTJ or INTJ, however, I differ. If you’re wondering about the I vs E thing, just remember that not all extraverts are social, just like not all introverts are recluses.
Mycroft just happens to show far more Te than he does Si.