Dive in mars as TV tropes - The Freudian Trio
Freud defined the human psyche as consisting of three parts: the Id, which represented emotional and instinctual desires; the Superego, which represented the logical and intellectual reasoning; and the Ego, which reconciled the Id and Superego. Likewise, the Freudian Trio consists of three characters: one who acts emotionally and instinctively, one who acts with cold, passionless logic and one who reconciles the two conflicting ideals.
River Thompson: The McCoy - The McCoy is emotional and humanistic. He cares about others deeply; for him doing the right thing is not a question of convenience or moral relativity, but about the concrete reality right now. Which is to say, someone like The Kirk cares about saving people; the McCoy cares about making things right. In Freudian psychology, this character represents the concept of The Id.
The McCoy still functions as an admirable character, however, due to his absolute devotion to his Moral beliefs and his refusal to give in to what others may tell him. For him, the only acceptable losses are those that are offset in the long run. In the McCoy's mind, every life matters and everyone deserves to be saved. While The Spock sees people as numbers in the greater picture, The McCoy sees people with real lives and emotions.
Diana Morgan: The Kirk - Rounding out the archetypal Freudian Trio with The Spock and The McCoy, The Kirk must balance these opposing personalities while being able to take their advice and choose between them without being overcome either by emotion or dispassionate logic, representing what in Freudian psychology is called the ego.
They usually share a lot of the traits of the Reasonable Authority Figure, but depending on the slant of the series he might lapse into less than heroic decisions, or end up choosing one of his two friends over the other more often. That said, the burden of deciding what course of action to take can be heavy, while the task of bringing his friends around to accept said decision is complicated as well.
Daniel Mars: The Spock - The Spock is an archetype that can be loosely summed up as the tendency to apply rules, reason and the greater good to all of his/her decisions. This character can exist by themselves, but more often, they will have a more emotional and humanistic counterpart to contrast his/her decisions. The main difference between the two archetypes is that while The McCoy will leap before looking, The Spock's solution to problems will have a balanced and well-thought out approach.
The Spock's relationship with his crewmates/comrades is often tense, because this character type is willing and able to ruthlessly consider ethically troubling situations without batting an eye — especially situations where people might be ordered to die. While his counterpart The McCoy is interested in doing the right thing regardless of cost to one's self, The Spock is only interested in the end result. For Him, everyone is expendable, especially himself, and he has no problem treating people as such.
