I write songs for singers. Rather, I write lyrics for composers to use for making songs - but, in my head, there is almost always an ideal performance of the lyrics by an ideal singer. Backing this up, giving it shape and rhythm, there is ghost music I can hear but couldn't ever write down, strum on the guitar or even hum for you.

The singers for whom I most often write are Dusty Springfield, Chet Baker and Billie Holiday. Holiday is a dangerous singer to dream of writing songs for. She was just too exquisite. How she sang "cry"; how she sang "time"! She could take shabby lyrics and break every heart in the room: "Love is like a faucet/It turns off and on/Sometimes when you think it's on, baby/It has turned off and gone." She could also take generalised lyrics and make them her own, while reinventing the melody as swingingly tenderly as her hero Louis Armstrong.

There are lots of songwriters who have had a bigger influence than Holiday on the lyrics that I write - Leonard Cohen, Paul McCartney, Elvis Costello, Jacques Brel. But, in a strange way, to have their voices in my head as I write would be an embarrassment and would probably cramp whatever style I have. These great writers don't need my words and theirs are best delivered in their own voices.

This is particularly true of Jarvis Cocker, another wonderful writer, whose book of selected lyrics, Mother, Brother, Lover, is published by Faber on 20 October. Most of the time, Cocker's words would suffer badly from being covered. I can't think of any other singer who could pull off the magnificently clumsy gabble of: "She told me that her dad was loaded/I said, 'In-that-case-I'll-have-a-rum-and-Coca-Cola.'" I can't imagine ever writing that couplet, partly because I don't drink rum and Coca-Cola but mainly because, to exist, it needed to come out of the excruciating experience of Jarvis.

The singers I dream I am writing for were all defined by cover versions - songs that they inhaled as someone else's and exhaled as their own. In writing lyrics, I don't want to steal the words from the singer before I have even handed them over. They have to be my sentiments exactly but they also have to be shareable, breathable.

For me, usually a lyric starts with something that I want to say but can't, or wanted to say but couldn't. I blurt it out on to the page, as directly as possible. This is the only way it might become emotionally useful to other people - which is what I believe songs should be.

The most popular pop songs are those that allow people to say something that they need to say - either to themselves, or to a particular person, or to the world: "My Way", "I Will Survive", "Someone Like You", "One Moment in Time". These are karaoke classics for very good reason: they connect, usefully. However, there's a point at which magnificent connection tips over into cynical manipulation - the natural home for which is Steve Wright's Sunday Love Songs (on Radio Two-ooo-ooo). Because it's so relentlessly cosy, my partner has developed a bizarre liking for this mawkfest. Yet she allows me to turn the radio off whenever Steve stoops to Luther Vandross's and Richard Marx's "Dance With My Father". If it's merely "Wind Beneath My Wings", I can inoculate myself by thinking of Brian Potter in Phoenix Nights, singing his tender version - "You Are the Wind Beneath My Wheels".

Beyond even these anthems are the songs, such as "Happy Birthday to You", which become ubiquitous. (An aside: a musician friend observed that even though most people aren't keen on contemporary microtonal music, if you listen to any group of ten non-musicians singing "Happy Birthday to You", it's about as extreme as atonality gets. What he hates even more than this, though, is professional musicians who harmonise the whole way through.) The greatest songs are those in which the words and music seem indivisible. If you asked me what my grandest ambition was, in co-writing songs, it would be to come up with "Twinkle, Twinkle, Little Star".

The nearest I've come, in terms of simplicity and inevitability, is in the lyrics for a song called "No Longer". (I co-wrote this with Chantal Acda of the Belgian band True Bypass. They're recording an album using my lyrics.) It's a song in the persona of a beautiful, ageing woman facing the mirror: "I knew the light and how to play with it/I'd take the night and spend all day with it."

There are trace elements of Cole Porter here, I am aware. And I'll admit to being a sucker for the cupcake cuteness of "Let's Do It, Let's Fall in Love", the sincere insincerity of "You're the Top" or the utter bonkersness of "My Heart Belongs to Daddy" - in which, having deliberately saddled himself with the "-addy" rhyme, Porter winds up rhyming it with "caddy" and "finnan haddie". This overstretching into the delightfully unexpected is a trick that everyone picked up from Byron's Don Juan. If a lyric writer isn't going for comic effect, they're best not picking a rhyme word that they're going to have to cheat on. Cohen worked this out years ago ("Hallelujah"); Bob Dylan occasionally struggles ("Shelter from the Storm").

Buried even deeper than Porter in verbal frippery is Noël Coward, although "Mrs Worthington" is redeemed by its bitchiness and "Mad Dogs and Englishmen" by the sheer tongue-twisting achievement of Coward getting through it without tripping up once. These are what I would call "numbers", though, rather than straight songs. And, as far as I'm concerned, the king of numbers is Brel: "Jacky", "Amsterdam", "Mathilde". Mon Dieu! No one else can whip words into such a frothing frenzy. I have had one serious go at the chanson that leaves the singer's life upon the stage.

It's a song called "What Haven't I?":

What haven't I known that I shouldn't
have known?
What haven't I dirtied? What haven't
I shamed?
What haven't I dreamt as I lay all alone
and my thoughts were untamed, and my
thoughts were untamed?

This is a long way from the simplicity of "Twinkle, Twinkle, Little Star". When a work of art is truly great, it becomes almost impossible to imagine it not existing. This, I think, is what nagged at McCartney after he'd written - or thought he might have written - "Yesterday". "For about a month, I went round to people in the music business and asked them whether they had ever heard it before. Eventually, it became like handing something in to the police. I thought if no one claimed it after a few weeks, then I could have it."

It's not cool to side with McCartney over John Lennon. In terms of the lyrical-musical pas de deux, however, there is no competition. Lennon was a heavy-footed hoofer whose ancestor was Carl Perkins and whose successors were Slade and Oasis - straight lines over a sludgy trudge.McCartney, coming out of a packed radiogram of music hall, musicals, the great American songbook and Buddy Holly, is far more of a Fred Astaire. His syncopations are delicious. He spends far more time in the air. Occasionally, this is because he's peddling fluff such as "Martha My Dear". Yet, at his best, he twinkles a lyrical line over a musical line like no other English songwriter. I have sung "Here, There and Everywhere" as a lullaby to my children for the past three years and it's still fresh to me, still a miracle of melancholy poise. I love and worship McCartney, whose progeny include Costello and Paddy McAloon.

Mostly I write lyrics for the composer Emily Hall. Her background is in contemporary classical music but she has been moving towards a more folky, poppy style. Where we meet is in aspiring to simplicity. One note, one word, not five, not two. So far, we've done a set of love songs and a song cycle - "Life Cycle" - about losing, having and loving a baby. These have been performed at the Purcell Room in London and the Latitude Festival. But as far as I'm concerned, our best success is co-writing a song that has become one of my children's lullabies.

Lightning over the sea.
Won't you dance a waltz with me?
Lightning over the sea.
Won't you dance a waltz?

Not "Twinkle, Twinkle", maybe, but something emotionally useful. And I can just imagine Billie Holiday swinging it.

Toby Litt's most recent novel is "King Death" (Penguin, £8.99)