You’d think, after four hugely successful albums, that Florence Welch would know her own voice. Yet the Florence + the Machine singer’s first lyrics and poetry collection is all about learning to speak. “What would I say / If it was just me / Not full of choirs, singing fucking constantly,” asks Song, its tricksily named keynote poem.

It makes sense. “Force of nature” is a cliche that Welch’s powerful voice often inspires, but it has a grain of truth: a song, for her, is something that blows through her from elsewhere. “I am a conduit but totally oblivious to its wisdom,” she says in her preface.

That sense of sublime submission to external powers prevails in the manic lyrics of her debut album, Lungs – here intercut with paintings by Waterhouse and prints by Morris, and Biroed scrawls on Chateau Marmont notepaper – in which love is a cosmic cataclysm, a werewolf possession, a train hurtling towards you. Rabbit Heart (Raise It Up) catches her quivering on the brink of global fame, “a rabbit-hearted girl / Frozen in the headlights”, sacrificing herself to a power that transforms her, only too aware that “it comes with a price”.

In Honeymoon, she feels the shells of those she’s hurt rattling behind her like Marley’s chains

On her second album, Ceremonials, she’s reconciled herself to that bargain, and become a semi-mythical persona, a floaty-gowned high priestess of catharsis (unlike many of pop’s posh set, the endearingly unedgy Welch has never tried to look like anything other than a privately educated art-school dropout whose middle name is Leontine). Oceanic feeling overflows in the likes of What the Water Gave Me, named after the Frida Kahlo painting, and making reference to Virgina Woolf’s suicide in the line “pockets full of stones” (Welch’s literary references led her fans to form their own book club).

By the time of her more naked third album How Big, How Blue, How Beautiful, she’s reined in the recklessness hinted at in Lungs’ Hurricane Drunk, and, on songs such as Ship to Wreck, is beginning to acknowledge that rather than being at the mercy of a vengeful sea, she may be the shipwright of her own self-destruction. Her most recent lyrics, on High As Hope, move even further from abstractions: instead of devils, demons, saints and stars, there is a frank admission in the opening lines of the lead single Hunger: “At 17, I started to starve myself / I thought that love was a kind of emptiness”.

Yet writing poems, Welch says, “has in many ways turned out even more exposing”. The first poem here, Song Continued, immediately begins to interrogate the difference. “This new voice, this ‘me’ voice / Is it conversational/ Confessional?” The poem debates which stories to give away, what face to present. Blackout-drunk tales for the addiction memoir age? An “aborted threesome”? She’s not entirely comfortable with these “muddy trinkets”, and mostly these poems find a more personal voice without trading revelations, continuing the movement towards the human scale charted in her lyrics. In Honeymoon, which makes reference to her song Shake It Out, she feels the shells of those she’s hurt rattling behind her like Marley’s chains. Catharsis, it seems, isn’t without collateral damage.

The new voice, in the end, emerges analytical, cooler, starker. Some of the final poems in the collection are entitled I Guess I Won’t Write Poetry and I Cannot Write About This, playing self-referentially with the strange, novel tone with a spare confidence.

Welch’s mother is a professor of Renaissance studies at King’s College London who worried about her daughter skipping university to focus on her musical career, lamenting “what a waste of a brain!” Both the lyrics and the poetry in Useless Magic validate Welch’s choice, offering a chance to appreciate on the bare stage of the blank page the fineness of her words. And like fellow poet-musician Nick Cave (thanked for “inspiration and encouragement” here), Welch has found a way for the song and the voice of the rabbit-hearted girl to coexist. As she says herself: “you can have everything”.

• Useless Magic: Lyrics and Poetry by Florence Welch is published by Fig Tree (£20). To order a copy for £17 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99