From restrained flirtation to a glorious shouting match

A programme of Beethoven and Mozart leaves the listener plenty to contemplate and an audience full of appreciation.

What happened to music between the reigns of Mozart and Beethoven? Their joint lifespan was barely more than 70 years. The latter was a devotee and would-be student of the former. And yet, as the London Philharmonia's performance of some of their greatest works on Thursday night made plain, the shift in sensibility could scarcely be more pronounced.

Music as Thought, a recent and fascinating book about Beethoven's symphonic style by Mark Evan Bonds, suggests that the composer's achievement was to break with a conception of music as being, in essence, rhetoric with the words taken out. He quotes Charles Batteaux's The Fine Arts Reduced to One Common Principle, from 1746, 10 years before Mozart's birth: "The word instructs us, convinces us: it is the medium of reason. But tone and gesture are the media of the heart; they move us, win us over, persuade us." And what is music, if not tone and gesture liberated from demands of language?

Well, for Beethoven it is wild nature served up straight. So, at any rate, his contemporary champions liked to suggest. But the great pleasure of a programme like Thursday's, in which Beethoven's Egmont Overture, Mozart's ninth piano concerto and Beethoven's fifth symphony were laid side to side for ease of comparison, is that you can form your own ideas. The Egmont Overture, written to accompany Goethe's play about the Spanish inquisition, is the sort of piece that the Finnish conductor Jukka-Pekka Saraste seems to handle particularly well - full of dizzy chasms of sound and mercurial tempo shifts. The groans of the double bass and delicate skeins of strings build to these great avalanches of timpani. And then, with a flick of the baton, Egmont is dead and free of oppression and his soul is free to exult, racing out of the depths on bright wings of violin and piccolo.

Saraste's dynamic command ensured that, however the passages of mortal terror might have accelerated, they never lost their mortal heaviness until that instant of triumph when the spirit threw them off. Mozart's ninth piano concerto couldn't help but seem like froth after such Manichean drama. But what froth. The piano soloist was a suitably Mozartean prodigy: Kit Armstrong, a straight-backed 17-year-old in a spearmint bow-tie. He played very much the way a straight-backed 17-year-old in a bow-tie might be expected to: polished, but lacking a certain spark of mischief.

If Mozart thought of music as a sort of rhetorical persuasion, there's no doubting what end he had in mind here. The allegro movement is an extended flirtation between piano and strings, the piano full of tickling trills and hyperbolic chains of arpeggios. Alas, in Armstrong's hands it felt rigid, a lecture rather than a frolic. The fluency was there; all that was lacking was a sense of the outrageous.

That rectitude started working rather well in the andantino, however, where the limpid melancholy of the score was somehow heightened by Armstrong's refusal to get carried away by it. The movement is full of wonderful feints where the strings swell and twist towards their home key before melting away, so that the piano steps over the threshold alone, with only a memory of the orchestra's gaiety to warm it. At these times the dignity of Armstrong's playing fitted the pathos of the moment admirably.

As for the rondo, where breezy briskness gives way to passages evocative of smiling reminiscence, his energy and discipline served the mood to perfection. Then it was the Fifth. Coming on the heels of so flamboyant a show of musical eloquence as the Mozart piano concerto, it's difficult not to compare it as another sort of rhetorical display. The famous line from Clauswitz sprang to mind, that war is the continuation of diplomacy by other means. Beethoven, of course, was writing in the shadow of the Napoleonic wars.

In the Fifth, the witty civilities of the classical era are replaced by bellowing, staccato exchanges: one section of the orchestra working in concert to shout down the other. We aren't yet in the realms of Romantic tone poetry: the impression is still of human voices in some half-heard disputation. But those voices are grown giant, carried on martial horns and drums. The orchestra worked with great precision here, most affectingly during those strange gusts of joyous brass that explode the peace of the second movement.

Even at its most pastoral, the Fifth is intent on proving how mighty the many can be when they speak as one. And that's how the audience - a full house, as far as I could make out - replied, standing to applaud and cheer as the musicians left the stage.