Functional Axis: Te/Ni/Se/Fi
Dominant Function: Te
Tom was methodical and systematic. His logic was objective, get things done logic. In this case, it took steps to achieve his goals. He started exercising his Te in school to systematically unearth his bloodline, then to extract Marvolo’s ring. From that point on, he calculatingly continued to frame people like Marvolo, Hagrid and Hokey. He took a job in the Borgin and Burkes, because it would give him access to powerful magical artifacts. His logic takes form of strategies and empirical plans that he executes, rather than subjective/‘unorthodox’ Ti.
Auxilliary Function: Ni
Tom’s Ni started showing when he was only a child. He already had a deep ingrained vision of his own specialty even before he knew he was a wizard. At the chapter ‘the Secret Riddle’ of the Half-Blood Prince, kid Voldemort was already well aware of his superiority and already had a clear sense of purpose. He intuitively found out his capability to converse with snakes. He went to Hogwarts and quickly had another vision, to investigate his lineage and to prove his superior bloodline. Then ultimately he had the grandest vision of them all: the ultimate superiority, immortality. His Ni left stamp everywhere, the Horcruxes he made were from objects that meant a concept to him. His internal symbolism was not ‘conventional’ but subjective. He had no trouble making an old diary and a living snake Horcruxes along with Slytherin’s locket: because in his mind, they all underscore Slytherin connection. He came up with the idea of 7 Horcruxes because of what 7 symbolizes (the most powerful magical number). His Ni shaped his entire worldview- everything he did later on only served to fulfill his grand vision-his superiority over mankind, both in evading mortal fate and in dominating the world.
Tertiary Function: Se
Voldemort’s Se seems to me baby Se, he is not quick on feat, every time he improvised, (like at the end of the Goblet of Fire, the Order of the Phoenix and the beginning of the Deathly Hallows) it backfired. In his moments of triumph, he can lose focus and fall prey to self-gratification (like after he was reborn, he dedicated an entire hour to monologue and theatricality).
Inferior Function: Fi
The number of times we are inside his head via Harry’s, we see him repeatedly consulting his own personal values, which are pretty well defined to himself. His morality is subjective and very unique, with no trace to his upbringing in Hogwarts or the orphanage (he developed bigotry and obsession with the purity of blood when he himself was half-blood and did not grew up in that kind of social settings). He views the world in a very black-an-white way. His Fi is unhealthy, so it caused him to take blunt actions over his ‘hurt’ feels (killing his entire paternal family). He is immune to criticism. And consistently relying on own morality/ethics resulted in him ignoring other people’s agendas, like Snape’s and Narcissa’s motivations for lying to him.
Note: This argument isn‘t from me. Look up the original source here: https://funkymbtifiction.tumblr.com/post/159201101778/harry-potter-tom-marvolo-riddle-lord-voldemort