4-D (The X-Files)

The episode's villain, Lukesh, was inspired by Alfred Hitchcock's 1960 film Psycho.

Writer Steven Maeda had previously written the eighth season episodes "Redrum" and "Vienen"; due to their success, Maeda was asked to pen a ninth season standalone episode. His efforts were hampered by the fact that, due to the departure of David Duchovny, the show had changed considerably. Maeda was inspired to write the episode after learning the story of a French journalist named Jean-Dominique Bauby, who had been paralyzed and could only communicate by blinking his left eyelid. Maeda thought the ailment was interesting and initially wanted to give it to a guest character for this purpose. However, he eventually felt it would be more successful if it affected a regular character, such as Doggett. Maeda employed the theory of parallel universes in order to explain the logistics of the episode. The character of Lukesh was in part inspired by Alfred Hitchcock's 1960 film Psycho. Maeda later noted that he wished to create a villain that would be as memorable as other antagonists in The X-Files, such as Eugene Victor Tooms and The Flukeman.[3]

"4-D" expounded upon the budding relationship between Doggett and Reyes. Most of the two's romantic interactions were limited to "flirtatious undercurrents" because, according to Annabeth Gish, series creator Chris Carter "was never big on the flamboyant big performances."[4] Robert Patrick later claimed that he came up with the scene in which Reyes shaves a wounded Doggett. He noted, "I'd read The Diving Bell and the Butterfly, and I believe there's a part of that in the book where the character gets shaved, and I thought, 'Wow, that's really an intimate kind of moment.'"[4]

Effects expert Mat Beck was instructed to create a visual sequence that showed Doggett and Lukesh traveling between the different universes.[3] Various effects were tested, including characters disappearing into black holes as well as phasing through the air in a more "exaggerated" and "watery" way.[5] Beck ultimately decided to use a combination of both effects. Separate shots of a morphing scene were taken: one of the actors, and one of the background. Beck then used software to morph the two together to make it appear as if they had vanished. Later, artistic touches were added in post-production editing to give a more futuristic effect.[3]

To create the effect of a parallel universe, every scene in the episode's teaser was flipped so that the mirror image was shown. In order to render words correctly, letters had to be re-written backwards so that they yielded the correct spelling. Monica Reyes' Georgetown apartment address is 67 Bennett Avenue. This is a reference to Rod Serling's address in Binghamton, New York. Furthermore, her apartment number 6, is a reference to Patrick McGoohan's number in the 1967 television series, The Prisoner.[6]

"4-D" first aired in the United States on December 9, 2001.[7] The episode earned a Nielsen household rating of 5.1, meaning that it was seen by 5.1% of the nation's estimated households and was viewed by 5.38 million households.[8][nb 1] "4-D" was the 62nd most watched episode of television that aired during the week ending December 9.[8] The episode was later broadcast in the United Kingdom on BBC One on November 25, 2002.[7]

"4-D" received mixed to positive reviews from critics. Robert Shearman and Lars Pearson, in their book Wanting to Believe: A Critical Guide to The X-Files, Millennium & The Lone Gunmen, rated the episode four stars out of five. The two noted that, while the episode's premise "doesn't seem as well thought through" as Maeda's past efforts, "4-D" is "worth it".[9] Shearman and Pearson concluded that the episode "earns its stripes by at last restoring to the series a pulse."[9] Furthermore, they praised Gish's performance, noting that she "finally [is] given a showcase that makes Reyes so much more than a New Age fanatic".[9] Christina Urban, in an editorial review of the ninth season for Barnes & Noble, praised the episode, calling it "by far the best of the season".[10] Jessica Morgan of Television Without Pity awarded the episode a "B". Morgan slightly criticized the episode's resolution, writing that it "explained nothing. I mean, how do these other universes work?"[11] In a season review, Michelle Kung from Entertainment Weekly wrote that "4-D" was one of the few ninth-season episodes "worthy" of praise, but that it was overshadowed by the show's "ludicrous conspiracy plots".[12]

Other reviews were more mixed. Zack Handlen of The A.V. Club gave the episode a "C" and called it a "mediocre to bad hour of television", but one that could have been better had more effort been applied to it.[13] Handlen was particularly critical of the editing, structure, and sense of urgency. He wrote that "'4-D' shows what happens when this creative team has a legitimately cool concept: it wastes the opportunity."[13] M.A. Crang, in his book Denying the Truth: Revisiting The X-Files after 9/11, felt that the interactions between Robert Patrick and Annabeth Gish were the "highlights" of the episode, but he was critical of the ending for wrapping things up "far too conveniently."[14]