Dominant Ni: Sherlock is wired for problem solving, He frequently makes logic jumps to pinpoint future occurrence and then works his way backwards to develop a strategy to prevent the outcome. His talent for reading people is almost supernatural, and because of his quickness to anticipate other people’s actions, he is able to adjust his plans accordingly. Though he loves problem solving, he isn’t overly fond of surprises because he’s used to being able to accurately predict everything. For instance, when Magnussen turns out to be far more dangerous than Sherlock originally deduced, he doesn’t have a backup plan to account for the surprise, and does the only thing that he can think of in the moment (this is Se acting up to foil Ni) and shoots him. Sherlock is incredibly focused on his work as a consulting detective and does not waver for anything. He thinks long-term, considering the consequences of his decisions before moving forward and allowing him to remain ten steps ahead of everyone else. He recognizes absurd, but totally logical patterns, but can’t always understand why no one else can see the things that he thinks are so obvious.
Auxiliary Te: Sherlock has a sarcastic tongue and rarely filters his words to make others feel comfortable. He corrects people’s grammar and choses his own words carefully (though not regarding how it will make others feel). He is quick to devise strategies for getting from Point A to Point B, and works through each step in detail without so much as stopping to explain his plan to anyone. Certain tasks seem menial to him in comparison to the wider problem (such as sending texts, or getting his own phone out of his jacket) and so he delegates them. Sherlock is usually comfortable with deadlines, but doesn’t like to keep to anyone else’s schedule. Most of his decisions are made without the input of his emotions, and he views the world through a logical lens. He perceives the universe as a maze of interlocking systems that can be navigated definitively “What do we say about probability?” “The universe is rarely so lazy.” Sherlock subconsciously views most of his opinions as fact (and he’s usually right), but this makes him come off seeming arrogant and rude.
Tertiary Fi: Sherlock is facially expressive at home when in the company of only a few people, but the moment you put him in a crowd, he assumes an awkward poker face. He’s embarrassed to feel fear and views most emotion as a hindrance, which must be eliminated at all costs. At the same time, we can’t deny that he is extremely emotional. He has very few friends, but he would do anything for them, even sacrifice his life and reputation so that they could live. He would rather they think badly of him than allow them to come to any harm. At the same time, he’s sensitive about becoming emotionally dependent on anyone, so he deliberately makes few connections with people. “Alone is what I have. Alone protects me.” Though he has a vast understanding of how people think, he’s a non-conforming thinker who doesn’t understand social rules at all. At parties, he doesn’t know how to behave and he often experiments with social taboos just for the fun of it. His principles are immovable. He refuses to kill unless he sees no alternative solution, and when Mycroft opts to let him walk away naked, he chooses not to.
Inferior Se: When focused, Sherlock is incredibly perceptive to his external environment. This allows him to make wild and accurate deductions because he notices all the minute details that the police miss. When external evidence is lacking however, he is less accurate in his assumptions. Moriarty deliberately leaves a mass of external clues in his wake, which is why Sherlock is so quick to unearth his schemes. Magnussen on the other hand, leaves no trace, and thus, Sherlock’s presumptions about his nature are regrettably wrong. When under too much stress, Sherlock acts in the moment, rather than thinking long term, and almost ends up going to jail as a result of an impassive decision to shoot Magnussen. Too much external noise and people overstimulate Sherlock. We can visibly see his dislike for being in front of cameras, and he leaves John’s wedding early because he doesn’t know what to do with himself there. At times, he can literally zone out of the physical world altogether, living inside the internal world of his mind palace.
I’ve seen him typed quite a bit as an INTP, however, he’s a clear Te user.