What first drew you to composing?

When I was 11, my parents divorced. My mother had custody and bought a place in Pennsylvania. I went to boarding school, but on the non-school days she, as a working woman, had to get rid of me. She had a passing acquaintance with the family of Oscar Hammerstein [II, the lyricist and playwright]. They had a son my age; we became fast friends, and the Hammersteins became my surrogate parents. I'd taken piano lessons when I was seven, so I had some musical instincts, but I really just wanted to follow in Oscar's footsteps. It was under his tutelage that I learned to write songs for the theatre.

What was your big breakthrough?

A show called West Side Story: I wrote the lyrics for it in 1957. I had written a show before that, for which I also wrote my own music, called Saturday Night. We were giving auditions for backers, and had raised about a third of the money, when the producer, who was only 40, suddenly died. The show went into limbo, and wasn't produced until many years later.

Which comes first: the music or the lyrics?

Oh, they come together. Always.

Is it true that you find whisky a help when writing?

No – I don't drink whisky, I drink vodka. And actually now I rarely drink at all, but if I do, it tends to be wine. I've always sipped something when writing lyrics, because it's the words that are difficult. Writing music is hard, too, but you can always just sit at a piano and move your fingers around the keys – even if you're not writing, you feel like you are. Lyric-writing is all sweat.

What changes have you seen to Broadway?

Just what's happened in the whole country: a dumbing-down. You don't get much in the way of straight plays; it's all musicals, and anything with daring and ambition will be done off-Broadway.

So had you been launching your own career now, would it have been more difficult to get started?

Yes, absolutely.

Which of your songs or shows are you most proud of?

I like them all for different reasons; it's like asking, "Who's your favourite child?" There's only one show I really think was a waste of time: Do I Hear a Waltz? I did it as a favour for some people; I wrote the lyrics, and Richard Rodgers wrote the music. It's an ugly metaphor, but I always compare it to a dead baby: it looks perfectly fine, but it does not have one moment of life.

What work of art would you most like to own?

[Georges] Seurat's drawings are among my favourite things, and I love a painter named Georges de La Tour. But when it comes to visual art, my feeling is that the works should be available for everybody to see. Owning art for oneself is not something I approve of.

What's the worst thing anyone ever said about you?

I remember a sentence from a British review of Sweeney Todd by a man named James Fenton, which went something like "Sweeney Todd is a tissue of bullshit from beginning to end". But hey, if you're going to have a thin skin, you're not an artist that's going to be reviewed. I try not to read my reviews, but there's always some friend who'll come along and, under the guise of trying to comfort you, let you know that you've been speared.

Is there an art form you don't relate to?

That's very interesting. I don't relate to classical ballet, though I do to modern ballet. And I'm impressed by architecture, but it's a bafflement to me.

Do you have any regrets?

Yes. I'm sorry I didn't have children.

Is there any truth in the adage that art is 1% inspiration and 99% perspiration?

That was said by Thomas Alva Edison, and there's some truth to it, absolutely. I'm old-fashioned – I believe in craft – and craft takes enormous amounts of sweat, whether you're building a table or writing a tune. All Edison was saying was that to have an idea is one thing, to carry it out is another. And the carrying out – the execution – is where it's difficult, and where it matters. That's what made the Seurat painting [A Sunday on La Grande Jatte, the inspiration for Sunday in the Park with George] such a lesson. He's got 500,000 dabs of paint in that thing, and each one is a decision.

In short

Born: New York, 1930

Career: Stage musicals include Company, Follies, Into the Woods, Sunday in the Park with George and Sweeney Todd. Has also composed scores for several films, and the lyrics for West Side Story and Gypsy. A new production of his show Merrily We Roll Along is at the Menier Chocolate Factory, London SE1 (020 7378 1713), until 23 February.

High point: "The first orchestral reading of any new score."

Low point: "The reviews of Merrily We Roll Along [in 1981]. They were very sneering and hostile; for a few months, I thought, 'I really don't want to be in this game any more.' But, like a cold, it passed."