We get hints throughout the book that Jack, who thinks he has extreme insomnia, in fact has Dissociative Identity Disorder, and that Tyler is in fact his alternate “nighttime” self.
Whenever someone else enters a room, Tyler disappears; when members of fight club see him, they obviously recognize him as Tyler; Jack himself talks about being Tyler’s mouth and his hands.
Instead it’s best seen as a neo-Situationist satire about the pitfalls of consumerism and about how our economic system pacifies and alienates its citizens.
Our hero in the book is an unnamed narrator who I shall call Jack, following the critical tradition surrounding the film.
Tyler Durden is Jack’s alter ego in the both the book and the film, a manifestation of Jack’s freer self.
As Jack himself admits, Tyler is brave, smart, funny, charming, forceful and independent.
The obvious theoretical influence on Fight Club is the situationism of Guy Debord and the Situationist International, a group of radical theorists and artists who published the journal International Situationniste and engaged in various radical artistic and political activities in France between the late 1950s and the early 1970s.
Their heyday was 1965-1968, when they had a strong influence on the student movement in France, leading up to the anti-Gaullist revolt in 1968.
In their focus on the sheer number of male bodies and on the violence seen in both the book and the film, they miss its more subtle critical message and the black humour that Palahnuik obviously intended.
David Fincher’s 1999 film version of the book is very true to this central message, though the immediacy of the image, with its depiction of copious quantities of semi-nude male bodies (notably Brad Pitt’s), has lead critics such as Lynn Ta and Henry Giroux to read its “real message” to be an attempt by white men to reclaim their masculinity within an emasculating, feminized consumer society and thus reinforce “patriarchy.” In other words, the film is a “regressive” moment within the late capitalist gender wars.