According to Nielsen Media Research, the episode was seen by an estimated 0.750 million household viewers and gained a 0.4 ratings share among adults aged 18–49.
A narrator (Jemaine Clement) in an undisclosed location, welcomes the audience, stating that the intention is to show a five-act story that encapsulates fear and empathy.
With David (Dan Stevens) still trapped inside his mind, the team concludes that he created an astral plane that blends reality and fantasy.
Ptonomy (Jeremie Harris) suspects David may have attacked Dr. Poole (Scott Lawrence) while trying to destroy the recorder but Syd (Rachel Keller) refuses to recognize it.
Melanie (Jean Smart) decides to visit a cryogenic room, where her husband Oliver lays frozen inside a diving suit.
Back in the astral plane, David is taunted by Lenny, who shows him an image from the real world where Ptonomy, Kerry and Syd (unaware that is Walter), are being driven in a van.
In January 2017, it was reported that the fourth episode of the season would be titled "Chapter 4", and was to be directed by Larysa Kondracki and written by co-producer Nathaniel Halpern.
[2] In its original American broadcast, "Chapter 4" was seen by an estimated 0.750 million household viewers and gained a 0.4 ratings share among adults aged 18–49, according to Nielsen Media Research.
The site's consensus states: "The strangest, most gripping Legion episode to date, 'Chapter 4' still moves the show's storytelling forward in a more traditional and illuminating way.
"[7] Alan Sepinwall of Uproxx wrote, "Tonight's Legion may be the weirdest, most abstract hour of TV I've seen since Twin Peaks ended.
"[9] Oliver Sava of Vulture gave the episode a perfect 5 star rating out of 5 and wrote, "The Legion creative team has to perform a challenging balancing act as the series splits time between mind-bending psycho-drama and X-Men-influenced superhero storytelling, and 'Chapter Four' is the most successful example of this dynamic yet.
"[11] Ron Gilmer of TV Fanatic gave the episode a perfect 5 star rating out of 5 and wrote, "I don't think we're ever going to get a purely linear show as far as plot goes, and that's great, but they moved the needle more towards standard storytelling, and that can only help.
Where exactly it got lost is hard to say, but the lighthearted quirkiness that has helped balance the show's darker, more philosophical themes isn't really featured — a bit surprising, as David and company's exploration of the astral plane should create more opportunities for surrealism, or just plain weirdness, than any plotline that takes place in real world.