Alright, let's start with the obvious: "i" and "The Blacker The Berry" sound almost nothing alike. The instrumentals, produced by Rahki and Boi-1da, respectively, reflect very different eras and genres of music, with the former being built around an almost completely un-doctored sample of The Isley Brothers' big hit "That Lady", and the latter featuring a trendy beat (that somewhat resembles 1da's "5AM In Toronto" beat for Drake) and a chorus from Jamaican dancehall artist Assassin. This stylistic disconnect means that "i" is something you could envision baby boomers dancing to, as it hearkens back to an earlier era of music and isn't very aggressive or abrasive. "The Blacker The Berry", on the other hand, features militaristic drums and a squall of distorted guitars, not to mention Assassin sounding like he's foaming at the mouth on the hook -- basically, not something you'd expect 60-somethings to love.
The there's the timbre of Kendrick's voice -- something that he's been known to alter within individual songs, sometimes even from one line to the next. Both of the new singles are no exception to this rule, as they both feature several of Kendrick's "voices," but if you had to make a cut-and-dry assessment, there's no question that he sounds angrier and rawer on "The Blacker The Berry". For the most part, "i" has him adopting a softer, more childlike tone when he raps and sings, which definitely adds to its uplifting vibe.
It's not everyday that a rapper follows up a positive track like "i" with a song that contains lines like "Sometimes I get off watching you die in vain" in its first 45 seconds. Yes, Kendrick adopts a much more nihilistic, biting tone ("I'm black as the heart of a fuckin' Aryan") on "The Blacker The Berry," no longer dreaming "of reality's peace" like he was on "i". Sure, plenty of negative things are mentioned on "i", but Kendrick walks away from them, preaching, "lift up your head and keep moving" as a method of coping and/or survival. With this and the unforgettable refrain of "I love myself" in mind, the internal struggle apparent in "The Blacker The Berry" is all the more shocking. Here, we see Kendrick falling into the depression and self-doubt that's only mentioned in passing on "i" ("I've been with depression ever since an adolescent"), with each verse opening with the line "I'm the biggest hypocrite of 2015" and Kendrick focusing in on the very issues he seems to ignore in favor of loving himself on "i". This time, he hones in on those who hate him and the fact that they made him a killer, asking them to "curse" him while admitting that he's also part of the problem at hand.
"i" opens with a monologue that sounds like a preacher declaring Kendrick something of a savior for his generation -- not unlike the "Black Messiah" described by a late Black Panther chairman on D'Angelo's recent track "1000 Deaths". It goes on to wrestle with many other religious themes -- the devil, holy water, Psalm 23:4 (AKA the "valley of the shadow of death" passage that Kanye's also referenced), "the good book", "the glory to the feeling of the holy unseen". In contrast, "The Blacker The Berry" deals with explicitly secular imagery, and makes no appeals to a higher power, presenting a grim portrait of life much more grounded in realism.
Whereas "i" deals with global and urban chaos exclusively in vague terms ("It's a war outside and a bomb in the street", etc.), "The Blacker The Berry" alludes to many current events. The concepts of the prison-industrial complex and the school-to-prison pipeline are hinted at, as is tribal warfare in Africa, and most auspiciously, the murder of Trayvon Martin. The mention of Martin, which appears in the penultimate line, is highlighted by author Michael Chabon as a "surprise revelation" that reveals the song's true meaning: Kendrick's hypocrisy stems from weeping for Trayvon while himself once being responsible for the death of a young black man. By painting in less broad strokes on "The Blacker the Berry", K Dot creates a contrasting effect between the two songs, which has its parallels in the work of other social justice-minded songwriters. If we imagine Kendrick as Bob Marley, "i" is his "So Much Trouble In The World" (an overarching, non-specific anthem for peace) and "The Blacker The Berry" is his "Buffalo Soldier" (a song that uses a well-defined historical moment as a symbol of black resistance).