Let's find out Narrator's type through analysing how he starts processing after his attention catches a stimulus, then how he proceeds in it, what kind of aid he takes, and the enclosure of the processing (interruptions are exception). We will take three situations for him, first one being with the start of the movie from the climax, second from when plane banks too sharply, and third from when he notices another faker Marla in his group. I won't be mentioning his interactions with Tyler because he is his own alter ego and thus the actual stimulus would be unknown to us. First situation, narrator is sitting tied to a chair with gun in his mouth. This stimulus triggers him to process the situation and he says, "For a while I completely forgot about Tyler's mass demolition plan and wondered how clean the gun was. With gun between your teeth you speak only vowels. All this, the guns, the revolution, the army, reminds me of the girl named Marla Singer." There is a clear use of a perceiving function, sensing to be precise. His focus being on sensory details without evaluating anything in the situation - The clean gun barrel, hearing how voice is when speaking with gun in your mouth, and then moving to next scene after mentioning Marla, to explain whole backstory, keeping the processing loop open. But there were clear signs for sensing. Second situation, he just finished up talking about accidents from car failure in his company with someone, and now when about to have his cuisine the plane banks sharply left. He says, "Whenever a plane banked too sharply on take-off or landing, I prayed for a plane crash, or a mid-air collision. Anything. When you die in an accident while being on a company trip, the travel agency pays you three times your last month's salary as life insurance." Again his processing is about sensation, but this time about inner temptation and alternative to boring life. Having heavy sensory experience of how crashing of a plane feels like to escape from mundane reality. And he mentions about the company's travel agency policy factually to explain audience how they work. Its a judging function of thinking to explain the mechanics and procedure of a policy, but not ridiculing it in terms of values. So there is a thinking function that is supporting the sensation. He is again interrupted as his sleep snaps. Third situation, he notices Marla who also just like our Narrator, fakes to have diseases and attends same support groups which Narrator does. How he processes it? He starts with explaining who Marla is. He says, "This chick Marla Singer did not have a testicular cancer. She was a liar. She had no disease at all. I have seen her at my melanoma Monday night group. And at Free & Clear, my blood parasites group Thursdays. And again at Seize The Day, my tuberculosis Friday night. Marla, this big tourist, her lie reflected my lie. And suddenly, I felt nothing. I couldn't cry, so once again I couldn't sleep." While initial sentences were common sense that a women can't have diseases specific to male. Though we can say they are being drawn from what he has observed. He proceeds to explain how she has been to different groups too to deduct why she is a liar. And closes the argument by referring to how he was again unable to sleep with his insomnia returning, and how he felt. "I felt nothing, I couldn't cry, and thus I couldn't sleep." A combination of sensing and thinking is noticed again. His dominant attitude appears to be of introverted type, which is flow of libido inward in reference to a subjective standpoint that filters information. And his monologues throughout has been about how his new experiences relate to what he is already familiar with, often backed by numbers, reports, and statistics (company policies, number of car accidents, and in general how the external systems function). This provides us an introverted sensing type with extroverted thinking auxiliary function i.e., ISTJ. "The smell from paper mills were like that of farts", "When I visited the fight club again, the floor was still hot from last night's fight. The aroma there felt like fried chicken." Auxiliary feeling wasn't a valid function in his case because there were no sufficient or strong instances where adjusting to external values helped him in sensory perceptions. Rather he was more factual, detached, and cold with his perceptions. So ISFJ as an argument fits less than ISTJ. An alternative to this perspective exists saying that Narrator could be an introverted intuitive type, mostly INFJ being argued. But introverted intuition being an intuition is about perceiving underlying meaning, development, potential, and trajectories. While most monologues by Narrator were about his sensory perception and not the underlying meaning behind his observation in abstract form. An INFJ Narrator if we have to consider, would have a natural orientation towards intuition and thus would have seek direct meaning in daily observation. And introverted intuition makes those meaning singular in form for being referred to internal impressions filtered through subjective factor. While our Narrator was not seeing the inevitable or single meaning. Instead he was perceiving concrete sensory observations and integrating them or aiding them with external logic and systems.