‘Eppur si muove’ — And yet it moves. Galileo’s defiant insistence that the Earth revolves round the Sun, his refusal to submit to the Inquisition, is a familiar one. It’s the battle cry not of a reformer but of a revolutionary, a passionate teller of truths.

It’s a credo he shared with composer Claudio Monteverdi. Born barely three years after the astronomer, Monteverdi faced his own inquisition. Defying those who would make music an immoveable sphere, bound in place by harmonic proprieties and structural conventions, he made works that rejected tidy formalism in favour of messy, fleshy humanity. His was music that moved in every sense, that lived as vividly as those who inspired it. He may celebrate his 450th anniversary this year, but Monteverdi was the first modern composer.

‘It solicits the ear and roughly, harshly strikes it… those dissonances are crude, ugly and insupportable.’ Provoking critical scorn with his experimentation long before Stockhausen or Boulez, Monteverdi’s musical prescience cannot be overstated. If Wagner is the father of contemporary music, then Monteverdi is its grandfather, transforming music from a beautiful act of artifice into one rooted in human truths and emotions, from a language that spoke only in smiles and affirmatives to one capable not only of mirroring but of challenging the world around.

‘The aim of all good music,’ Monteverdi wrote, ‘is to affect the soul.’ This agency took many forms — the expansive variety and soaring beauty of his 1610 Vespers, the deft character-portraits of his late operas — but nowhere is it more richly explored than in the composer’s madrigals, a sequence of secular works of unprecedented emotional breadth, a musical rival to the sonnets of Petrarch or Shakespeare.

When we think of a great composer we think of symphonies — large-scale works that carry the weight of moral and social conflict; of heroic struggles against authority, and of strength in adversity. In short, we think of Beethoven. It’s his model we see echoed in Tchaikovsky, Berlioz, Mahler, Shostakovich, even Wagner — composers of big, troubled works whose musical conflicts in turn mirror those of their complicated lives. It’s a Romantic archetype that struggles to assimilate composers who operate at their best on a smaller scale. Schubert’s lieder carry all the weight of a symphony but enjoy little of its stature; the compact scope of Byrd’s motets belies the intensity of their spiritual and political struggle; Haydn’s string quartets are treated indiscriminately as tuneful coffee-concert affairs.

And so it is with Monteverdi. His three surviving operas are masterpieces — some of the very earliest in the genre still regularly performed today — but they are part of the problem, distracting us from the true revolutionary heart of his music. Monteverdi’s eight books of madrigals span more than 40 years of his life, and condense the emotions of that lifetime into a sequence of miraculous miniatures that hit the ear with shocking force. A narrative in thrall to greatness, which cannot forget the operas, sees these madrigals as apprentice pieces, growing in sophistication and innovation until they graduate to the late, great works — Il ritorno d’Ulisse in patria and L’incoronazione di Poppea. But this is writing history backwards.

The word ‘madrigal’ is not a fashionable one. These secular songs have been thoroughly debased by the Victorians, who drained their rich colours into consumptive pastels, beribboned their melodies with coy fa-la-la-ing. Monteverdi’s madrigals couldn’t be further from this anaemic genre. Part of their strength lies in the difficulty of identifying precisely what they are. The composer’s madrigal books contain everything from duets to dramatic scenas, scored for forces from a single solo voice and continuo to eight voices. And they are far from being isolated miniatures. Many are strung together into dramatic sequences that offer contrasting snapshots of a single relationship or situation — a montage before its time.

It’s precisely this flexibility of form, its endless adaptability, that gives the madrigal its power. The quality of the texts is also far higher than in opera, where libretti often represent awkward compromises or multi-author composites. The madrigal allowed Monteverdi to work with his artistic equals — to let poetry by Tasso, Petrarch and Guarini become the ‘mistress’ of his music.

But where to start? The early Books I–III belong to the stylistic world Monteverdi inherited, while the Ninth is a posthumous collage of trifles. The real interest begins in Book IV. Craving a new expressive freedom, the composer frequently breaks off from polyphony, ripping through these carefully woven textures with freely declaimed text. The effect is electrifying — just listen to the erratic beauty of ‘Sfogava con le stelle’, in which a lover pours out his heart to the same stars that watch over his beloved. The arresting breaks in the texture pull the ear back again and again with their direct, unmediated appeal. This is emotion flayed raw.

But if Book IV fires a warning shot across the bow, Books V and VIII launch an all-out musical assault on convention. For the first time an instrumental basso continuo part appears, providing continuity that allows voices to falter, stop altogether or even sing alone. Suddenly, musical emotion is less a matter of symbolism than of imitation; sighs, moans and shouts of joy can all be rendered truthfully, with each voice unshackled from its fellows. Harmonically, too, things are very different. The knife-twisting dissonances that famously angered the theorist Artusi in ‘Cruda Amarilli’ (‘A tumult of sounds, a confusion of absurdities, an assemblage of imperfections’) turn the poem’s cardboard lover into something of flesh and blood, someone whose thoughts alternately gallop and linger, whose emotions ebb and flow naturally, if unpredictably.

Book VIII is the greatest and widest-ranging volume of secular music of its age — perhaps of any. Composed over a 30-year span, the madrigals tackle not only the erotic charge of love and sexuality, but also for the first time its warring conflicts — the restlessness, agitation and rage that go hand in hand with its pleasures. No single work can represent such a collection, but perhaps the ‘Lamento della Ninfa’ comes closest; if you listen to just one work, make it this one.

Instead of setting this story of a nymph’s despair over her faithless lover as a strophic madrigal, mirroring the verses of the original poem with descriptive music, Monteverdi instead dramatises it. The nymph’s impassioned first-person speech runs continuously through the middle of the texture, a stream of freewheeling, recitative-like grief that winds and coils itself around the choric music of the three shepherds who narrate her story. The music unfolds with breathtaking spontaneity, eschewing the confines of an orderly musical form. Although ragged and at times uneven, the effect is profoundly modern, its shifting uncertainties held together by the musical thread of the inexorably repeating bassline. We close in an eerie tranquillity; despair has given way to sobbing silence, and circling harmonies to stasis. All is still. And yet, it moves…

If Wagner is the father of contemporary music, then Monteverdi is its grandfather

I Fagiolini perform a selection of Monteverdi madrigals on 22 February at Sir Jack Lyons Concert Hall, York. Les Arts Florissants’ latest Monteverdi recording, Madrigali, Vol. 3, is now available on Harmonia Mundi. John Eliot Gardiner and his Monteverdi Choir and Orchestra will perform a complete cycle of Monteverdi’s operas at Bristol’s Colston Hall from 12 April.