Richard Rodgers: With a song in his heart

Big events demand big statements. Here's one: Richard Rodgers was the greatest, the most naturally gifted, the most versatile popular melodist that ever lived. For more than six decades, he blessed the musical theatre with some of its sweetest sounds. He wrote more than 900 published songs – that's 300 up on Schubert (with generally smarter lyrics) – and 40 Broadway musicals. With Lorenz Hart, his first enduring partnership, he perfected the sound of regret, a bitter-sweetness that owed much, as Rodgers himself once put it, to the clash between "sentimental melody and unsentimental lyric". Hart's caustic rhymes tugged away at what Cole Porter once described as the "holiness" of Rodgers's tunes. Rodgers, in turn, gave Hart's more capricious lyrics shape; he made them sing. Together, they were modern-day Savoyards. They had wit, wisdom, and countless ways of saying "I love you" in 32 bars.

With Oscar Hammerstein II came a whole new deal – an open-heartedness with stars in its eyes. But something else: an ability to build character into storylines and storylines into drama. Oklahoma! (1943) changed the way people thought about musicals. The play – the "book", as it's known in the trade – was the thing; the music gave it a reach and an exuberance hitherto unimaginable in this most popular of genres. For Rodgers, for Hammerstein, it was a beautiful morning and most everything was going their way.

That great show returns to Broadway next year in the revelatory Trevor Nunn/ National Theatre production that so startled Mary Rodgers, the composer's daughter, with its freshness and dramatic truth that she was convinced Nunn had added things to the book. He hadn't, of course. He and his stellar cast just knew how to unlock it.

Mary was the first of two daughters born to Richard and Dorothy Rodgers. She grew up to the sound of her father's piano. As a little girl, she was convinced that he wrote every song she ever heard. He didn't lock himself away when he worked. The door was open, the melodies wafted through it. Finding them wasn't an agonising process for Rodgers. They came as naturally to him as to us. "With a Song in My Heart" (a favourite of mine from the show he wrote with Hart in 1929 – Spring Is Here) might be his signature tune. The uplift and elation of the melody can be attributed, we're told, to his first aeroplane flight. Anything might trigger the inspiration. Writing tunes was what he did; he adored it, it was a constant high for him. Mary remembers how the songs seemed to sit quite naturally under his fingers.

Her son Adam Guettel – composer of the masterly Floyd Collins (good genes in this family) – remembers the prominence of his grandfather's right hand, melody not harmony leading the ear. "A great melody," Rodgers told him, "implies its own harmony." Significant words. Lesser melodies hide behind the harmony. Rodgers' melodies don't need to. The next note is somehow inevitable the second after you hear it. But what makes one simple Rodgers phrase so utterly distinctive and memorable where another's is just simple? Sometimes it's merely a question of one or two unexpected notes, a displacement, an inversion, a quirk of rhythm. Rodgers could look at his work afterwards and identify the musical processes at work, but the creative process was much more intuitive. Says Mary: "He couldn't tell you why he did something, just that he did it."

She recalls how Stephen Sondheim once asked her if she could fix up a meeting between her father and himself. Easily done. But if Sondheim was hoping for an illuminating private seminar (and, of course, he was), that's not what he got. In answer to every question as to how or why he did certain things, Rodgers would reply: "I haven't the faintest idea." The bridge passage or "release" of "People Will Say We're in Love" from Oklahoma! is a simple inversion of the opening phrase (to give the melody symmetry), but when Sondheim excitedly drew his attention to this fact, Rodgers denied that the thought had ever crossed his mind.

He often denied the concept of inspiration, claiming that even a score as inspirational as Carousel (his personal favourite) was merely the product of hard work. For a man who, by all accounts, so successfully concealed his emotions during childhood, this of all his scores was a release. A song like "What's the Use of Wondrin'?" has very little to do with hard work. The ache in the melody comes from somewhere deep inside, and the payoff – "You're his girl and he's your fella/ And all the rest is talk" – is as simple and profound a line of lyric as Hammerstein ever penned.

But such feelings are always easier to recognise than to describe, especially when they are your own. Rodgers surely underestimated just how finely tuned and highly developed his "gift" was; his critics did, too. Consider a much-maligned and oft-parodied song like "My Favourite Things" from The Sound of Music. Merrily we sing along with the first four-bar phrase, merrily we repeat it, but don't anyone tell me that there isn't a touch of genius in what happens to the melody when we spy the "brown paper packages tied up with string". A lesser talent than Rodgers could labour from here to eternity to tie it up so memorably and so effortlessly. But it's easy to snipe. Kenneth Tynan described Rodgers and Hammerstein's 1958 show Flower Drum Song as "the world of woozy song". Clever line, cloth-eared response.

Mary Rodgers – in London for previews of Trevor Nunn's South Pacific, which opens tonight at the National Theatre – is a great ambassador for her father's work because, as a composer and writer herself, she knows where it's come from. Being Richard Rodgers' daughter was never an inhibition for her. Being a woman was. All of which made the success of her own 1959 Broadway show, Once Upon a Mattress, that much sweeter. Her father, who was never falsely encouraging about her work, was genuinely enthusiastic about it. Except for one song – "Yesterday I Loved You" – which she played him in the early stages of writing. "I wouldn't have changed tempo in the bridge," he said. And she said: "An alarm went off in my head. I thought, if I don't cut this off at the pass right now, then I will never know – and neither will anyone else – who is writing my music." It was the last time she played anything for her father until it was ready to be heard.

She doesn't compose any more. "I know exactly where I hang in the firmament. I'm not disrespectful of my ability, but I know that I'm not my father nor my son." She once found herself giving Adam advice, rather as her father had given her. "It's nice to come home," she said to him, "to get back to the original key." But even as she said it she realised that he was so far beyond her that he could never come back.

Right now, she is full of South Pacific. Trevor Nunn won her trust with Oklahoma!. She's confidant he'll do it again. There are things that have been restored to Act II that she has always loved, but whether they will still be there tonight, she cannot say. As a parting shot, she shares with me one of her father's favourite opening-night gambits: "How do you think it went?" Trevor Nunn should be ready for that.

'South Pacific' opens tonight and runs until 27 April, Olivier, National Theatre, South Bank, London SE1 (020-7452 3000)