The band halted recording of the first part after lead singer Matty Healy left for a drug rehabilitation clinic in Barbados, seeking treatment for his heroin addiction.

Eschewing metaphors and ambiguity, the album utilises black humour, simple lyrics and straightforward storytelling, covering dark topics such as nihilism, suicide, depression, anxiety, dissociation, trauma, cynicism and death, among others.

In an April interview on Zane Lowe's Beats 1 Radio show, the singer confirmed the title Music For Cars and announced a 2018 release,[5] saying "[the album] has always been called that, and we were always gonna do a trilogy of records".

[7] With Music For Cars, the singer aimed to create the most important pop album of the decade, hoping to achieve the same impact as Radiohead's OK Computer (1997) and the Smiths' The Queen Is Dead (1986).

[8] In August 2017, the 1975 stated they were in the editing process of Music For Cars, having over two hours worth of material,[9] while the band's manager Jamie Oborne said the first recording sessions for the album were planned for September.

[15][17] In September, the singer went on a tirade while under the influence of benzodiazepine, proclaiming he would continue to smoke heroin while telling the band members: "Listen, everyone has to get onboard because I'm the fucking main deal.

[18] Healy spent seven weeks in Barbados between November and December, an experience that inspired several songs on A Brief Inquiry into Online Relationships; he used songwriting as a means of catharsis that allowed him to gain a sense of purpose and wellbeing.

[40] The Daily Telegraph's Neil McCormick observed a "kaleidoscopic" variety of styles that reflects the album's engagement with contemporary culture and noted the presence of aesthetically unifying lyrical, vocal and instrumental factors.

[41] Writing that the record combines a "strange" mix of tones, genres and production into a singular aesthetic, Mike Watkins of Clash opined that it continues the experimental progression of I Like It When You Sleep, for You Are So Beautiful yet So Unaware of It.

[53] Interspersed with ambient interludes, the maximalist songs on A Brief Inquiry into Online Relationships are characterised by spaced-out electronic beats and flourishes,[54] gospel choirs,[46] saxophones,[55] neo-soul horns,[56] light piano, 1980s synths, "jaunty" melodies and downtempo rhythms.

[19] Several overarching narratives connect the record:[31] society's relationship with technology,[46] the millennial experience in the information age, and Healy's commitment to sincerity following the end of his heroin addiction.

[31][62] The record eschews condescension and generalisation in an attempt to embrace contemporary life,[60][35] utilising straightforward storytelling and simple lyrics that omit metaphors and ambiguity.

[43][63] Biddles opined that the album is "ostensibly about the internet's role in our lives", writing it continues the band's exploration of how people connect and what messages are lost through digital communications.

[44] Writing for Atwood Magazine, Sara Santora felt the record reflects the effects of social media addiction and the 24-hour news cycle on youth culture, causing millennials to be "constantly concerned with the state of our world".

[33] A Brief Inquiry into Online Relationships attempts to document the millennial experience in the information age,[61][65] serving as a cautionary political statement about modern society and contemporary existence.

[33][68] Regarding the impact of these events on the album's themes and lyrics, Stereogum's Ryan Leas said it depicts: "The static, the paralysis, the disenchantment, the fury, the dislocation, produced by a world that seems to be falling apart and the way the internet brings that right up to our faces constantly.

"[68] Abandoning postmodern irony and embracing sincerity, A Brief Inquiry into Online Relationships marks a definitive shift toward an honest dialogue about Healy's sobriety and recovery.

[19][31] Although reluctant to speak on his addiction, the singer did not want to romanticise or trivialise it and sought to avoid the "clichéd myth of the countercultural rebel junkie", using the lyrics to deter any fetishisation of his struggle.

[69] Writing for The Irish Times, Louise Bruton described the record as "[wandering] through the various darkened states of isolation until it finds faint glimmers of light to reach out for", covering dark subjects such as suicide, depression, anxiety, dissociation, trauma, disillusionment, self-loathing, cynicism and death.

[75][76][77] Characterised by minimal lyrics which detail how Healy lied to his friends amid his addiction, "How to Draw / Petrichor" is a two-part experimental,[60] electronica,[41] ambient and UK garage interlude.

[90][91][33] Siri performs the album's ambient spoken word intermission,[92] "The Man Who Married a Robot / Love Theme", a satirical poem about society's willingness to sacrifice human connection for virtual gratification.

[35][46] "Mine" is a jazz and lounge ballad which discusses a fear of commitment and fighting crime online,[35][97] featuring brushed drums and a trumpet solo by Hargrove.

[114] The track was certified silver by the British Phonographic Industry (BPI), denoting sales of over 200,000 units in the UK,[115] and earned a nomination for Best Rock Song at the 62nd Annual Grammy Awards in 2020.

[167] In a perfect five-star review, Harris praised Daniel's "beautiful" production and the musical variation present throughout A Brief Inquiry into Online Relationships, ultimately deeming it a "considered, ambitious album from a band who are constantly pushing themselves".

"[80] Pitchfork's Ryan Dombal highlighted the record's "boundless sense of style", writing that Daniel and Healy's production feels "more purposeful" than that of I Like It When You Sleep, for You Are So Beautiful yet So Unaware of It.

[93] Gormely commended the 1975's ability to incorporate retro and contemporary influences to create music that sounds "new and familiar", and said their willingness to "fall flat on their face" distinguishes them from the "inoffensiveness of their pop peers".

[45] Awarding A Brief Inquiry into Online Relationships a perfect five-star review, DIY's Will Richards deemed it a "bombastic, immaculately put together portrait of modern life", writing that the album's themes and lyrics transmit the feelings of youth culture.

[60] McCormick also commended Healy's songwriting, noting that the singer "easily [shifts] from witty sloganeering to tender confessional", while saying a "tone of urgent honesty pulses through the album, a visceral need to connect".

[40] Writing for the Los Angeles Times, Mikael Wood wrote that despite being an "excellent [and] often thrilling" record that demonstrates Healy's understanding of such issues, the singer fails to recognise that he is "also more of a contributor than he likely realizes".

[47][178][99][179] Addressing the similarities in his review of the former album for The Boston Globe, Issac Feldberg felt it does not share the same sense of "doom and gloom" as OK Computer, and instead projects "its vision of life in the information age [as] too textured, too lived-in, to indulge the same shallow sanctimony that's hamstrung recent, analogous efforts by other artists".