The National Theatre version of A Little Night Music - that nostalgic- astringent valse tragi-comique of misdirected yearnings - gives back a song called "My Husband the Pig" to the betrayed but still besotted Countess, a woman whose dolt of a dragoon spouse actually expects her to help him fight off any rivals for his mistress's bed. In the Countess's song of clear-sightedly incurable humiliation, the romantic cliche of worshipping the ground that someone walks on is acerbically wrenched askew so as to describe a situation resolutely devoid of dignity: "I worship the ground / That he kicks me around / On, the pig".
The analytic wit that can pin down a perversity - of which the singer remains the conscious, hapless and conniving victim - is a gift shared by many of Sondheim's characters. Rather than give vent to inchoate feeling when pressed, his people tend towards mordantly precise self-dissection. It's their way of staying (or seeming to stay) in control. Control is something not easily surrendered in Sondheim's world. One of the reiterated lines in a trio from Night Music sings of "Keeping control, while falling apart" and control is a prerogative which the 35-year-old professional- bachelor hero of Company is starting to feel ambivalent about wanting to preserve.
The first half of Sam Mendes's excellent production, now transferred to the Albery Theatre, closes with the previously deleted song "Marry Me a Little". The title, with its knowingly absurd qualification (equivalent to asking someone to "make me a trifle pregnant") indicates the problem. "Marry me a little / Body, heart and soul / Passionate as hell / But always in control": Adrian Lester's Robert itemises these self-protective provisos ("We'll build a cocoon / Of love and respect / You promise whatever you like / I'll never collect") with a mounting edge of desperation, as if he knows that the more he protests "I'm ready!", the more anxious and hollow his fervour sounds.
You sense that Robert would have no problem identifying with the sentiment expressed in the title-song of a very early Sondheim musical, Anyone Can Whistle (1964): "Maybe you can show me how to let go / Lower my guard, / Learn to be free". There are those who feel that the lines that precede these - "What's hard is simple, / What's natural comes hard" - apply equally to the man who wrote them: he's clever about inhibition because he's an inhibited smart ass. The lyricist Sammy Cahn has said of Sondheim that "he's scared to say I love you", while Leonard Bernstein, a composer never afraid to sport his heart on his sleeve, once spoke of Sondheim's "fear of corniness, or being platitudinous" and of his "reluctance to make a direct subjective statement".
What, you wonder, would they all make of Passion, a musical where the expression of love dispenses (in theory) with the composer's customary strategies of indirection - the prophylaxis of pastiche (as in Follies), or a context of undercutting irony (as in Sweeney Todd, Assassins et al)? This is, indeed, to put it mildly. Based on an 1869 novel by Igino Tarchetti that became Passione d'Amore, a 1981 film by Ettore Scola, the new work, set in the Italy of 1863, focuses on a fixated, unrelenting, unqualified love. "Loving you / Is not a choice / It's who I am," sings Fosca, the ailing, pitiably plain heroine, to Giorgio, the handsome, sensitive young officer who has become the object of her undeviating devotion. From love as something to be dithered over to love as absolute destiny: the change in Sondheim's approach is surely profound?
My own view is that Passion both is and isn't a departure for him. It isn't, because Fosca can be seen as taking her place in the long line- up of obsessives who have featured in his work. Think of Seurat and his pointillist experiments in Sunday in the Park with George or of John Hinckley Jr in Assassins, with its gun-toting chorus of nine people, all of whom have used the president of the United States for target practice; it's a musical which convinces you that these people, far from being incongruous figures in this art-form, simply took the genre's values ("In the USA / You can work your way / To the head of the line") to a dark, lunatic loser's extreme.
It's significant that the only show, before Passion, that Sondheim wrote on his own initiative rather than at someone else's suggestion was Sweeney Todd. It's also significant that, in this latter, the most intense of the love songs is the rapt, hushed hymn of reunion which the hero delivers to his razors, so absorbedly that he doesn't even hear the parallel, potty outpourings of Mrs Loveit, the pie shop owner who is equally monothematic about him. The sequence disturbingly demonstrates how honourable impulses in Todd (anguished love for his daughter and frustration at the injustice she and he have suffered) become warped by obsession and feed into a self- deluded, homicidal moral crusade.
Where Passion differs is that, for the first time, the obsession of a Sondheim protagonist proves to be both amatory and redemptive. In this piece, it's as though the divergent tendencies within the composer's work have been forced into a dream-like, cataclysmic collision. Giorgio, who is having an affair in snatched afternoons with a married woman (Clara), represents the kind of cautious, self-possessed psychology which likes to keep its affective life in safe compartments. Fosca, by contrast, is possessed rather than self-possessed, her ugliness, illness and desperation having pushed her to a point beyond inhibition. An unnerving mix of the selfish and the selfless, she pursues her quarry with a dogged, demanding persistence. Her unconditional love, viewed by him at first as a repellent dependency, eventually works a spiritual transformation on Giorgio, but only just in time. This is not a work that will give false consolation to the unattractive.
The other reason why Passion is not a complete departure is that Sondheim has not abandoned indirectness. Much of the drama is conducted through letters, whose contents are sung by the recipients as often as by the senders. The obliquity this bestows on the proceedings has a dramatic power best exploited in the scene where Fosca dictates to Giorgio the letter she would like to receive from him.
It is she, therefore, who sings wishfully of the awe she is willing him to feel: "For now I'm seeing love / Like none I've ever known / A love as pure as breath / As permanent as death / Implacable as stone..." Sondheim is more renowned for intricate verbal effects than for deceptive simplicity but it's hard to see how he could have evoked Fosca's ambiguous absolutism better than in the stark interplay in those lines between the life-giving and the deathly. "As obdurate as stone" would be the conventional simile: to call it "implacable" is to endow its resisting hardness with an eerie living force.
Sondheim has often had trouble with his endings. As with the willed optimism at the close of the revised version of Follies, unveiled here in 1987, the "Being Alive" conclusion of Company is less true to the logic of what preceded it than is the laceratingly sceptical "Happily Ever After" ending that was dropped. As a lyricist, Sondheim is fond of havering, Janus-faced compounds - "sorry-grateful", "regretful-happy" - but, as a musical dramatist, he has sometimes succumbed to the pressure to stop equivocating at the finish. In Passion, however, where death and breakdown co-exist at the end with the spectral sense of a transfiguring emotional legacy, the material permits him to pull off a conclusion that is heart-stoppingly desolate- radiant.
n 'Passion' now previewing at the Queen's Theatre, Shaftesbury Avenue, London W1 (0171-494 5040), opens Tuesday. 'Company' is at the Albery, St Martin's La, WC2 (0171-369 1730). 'A Little Night Music' is in repertoire at the RNT (0171-928 2252)