In 1788, Bach’s music came to Vienna. His epic choral piece Die Auferstehung und Himmelfahrt Jesu had already been received well in his native Germany – and now the oratorio, vividly evoking Christ’s resurrection and ascension, was to be performed in the music capital of Europe. Mozart himself took up the conductor’s baton, and the piece beguiled both Haydn and Beethoven. Over a career spanning five decades, Bach would win similar plaudits again and again. Beethoven swore by his treatise on keyboard music, while Mozart was even more forthright. ‘Bach is the father,’ he declared. ‘We are the children!’

This praise is striking enough in itself, but the truly extraordinary thing is who it was aimed at. The composer of Die Auferstehung, after all, was not the Bach we know best today, a man of sober wigs and pudding-thick Lutheran faith. Rather, Mozart’s musical icon was the old man’s son, Carl Philipp Emanuel Bach, born when Johann Sebastian was almost 30. Indeed, during their own lifetimes, CPE Bach would prove more popular than his father, dragging music away from the glory of God, towards a sensual individuality many modern musicians would recognise. More than that, his meandering path from fame to obscurity and back again speaks poignantly to the fickleness of fashion, and the difficulty of knowing how you’ll be received once you’re gone.

Johann Sebastian Bach had several musical children — but none was as remarkable as Carl Philipp Emanuel. Unlike his father, who toiled for years in obscure, provincial Leipzig, his son quickly secured work at the cosmopolitan court of Crown Prince Frederick of Prussia. ‘The greatest and noblest pleasure which we have in this world is to discover new truths,’ the future Frederick the Great once proclaimed, and the younger Bach obviously felt comfortable among Berlin’s cultural elite. A frequent visitor to the city’s salons, he met writers such as Karl Wilhelm Ramler and philosophers like Gotthold Ephraim Lessing. This fascination with Enlightenment culture would endure. Later in his career, in Hamburg, he discussed literature with distinguished poets, and by his death had acquired over 400 portraits, each depicting artists and thinkers he admired.

With his austere claim that the point of music was for ‘the glory of God and the refreshment of the soul’ – and the time he told a bassoonist he played like a ‘nanny goat’ – it seems hard to imagine the elder Bach relaxed at an aristocratic salon. And if the two Bachs varied in temperament, so too did they part ways in musical taste. Where the father perfected an older type of baroque music, crafting miracles of counterpoint and structure, the son grasped something new. A major proponent of a style called Empfindsamkeit  (Sensibility), Carl Philipp Emanuel’s music presaged Romanticism in its intensity and fire. Listen to his solo keyboard works, the composer’s favourite form, and you can hear this. Allegro movements recall Beethoven in their erratic tempos; slower pieces yearn and ache like Chopin. Sometimes, Bach’s influence is even more explicit: Haydn’s grand oratorios were inspired by Die Auferstehung, which apparently also influenced Mozart’s Requiem.

Nor did the so-called ‘Berlin Bach’ keep his musical radicalism to the concert hall. On the contrary, he used writing to inject a new emotion into the art form, arguing that music should come ‘from the soul’. That’s shadowed by a distinctly modern approach to performers themselves. If his father’s musical philosophy was characteristically low-key – anyone could ‘achieve the same results’ with enough work – CPE Bach saw soloists as showmen. ‘Since a musician cannot move others unless he himself is moved’, he wrote in one essay, ‘he must of necessity feel all of the effects that he hopes to arouse in his listeners.’ No wonder the younger Bach was one of the first musicians to write an autobiographical account of his life, even as his letters are filled with hope that he would ‘not so soon be forgotten in the future’.

The irony is that, for centuries, CPE Bach was hardly remembered at all. He may once have been Mozart’s musical mentor, even as the father sometimes called ‘Old Bach’ was dismissed as outmoded, but by the following century the situation couldn’t have been more different. ‘As a creative musician he remained very far behind his father,’ sniffed Robert Schumann in the 1830s, while a later edition of the Encyclopedia Britannica reported that the young Bach ‘was a somewhat feeble imitator of his father’s style’.

Modern scholars have tried to understand how CPE Bach’s reputation tumbled after his death. One argument involves the frantic turbulence of his music, with one expert suggesting it risks muddling listeners and frustrating performers. Another theory claims the young Bach slipped between the cracks of musical historiography. If, after all, Johann Sebastian Bach is now considered the master of the baroque, Wolfgang Amadeus Mozart the genius of the classical symphony, and Ludwig van Beethoven the tempestuous father of romanticism, Carl Philipp Emanuel arguably straddles all three periods. Ironically, the young Bach may have helped shape these distinctions himself, preserving his father’s unpublished works and co-authoring his obituary.

In a broader sense, however, such worries feel increasingly irrelevant. Especially since the 300th anniversary of his birth, in 2014, interest in CPE Bach and his startling, spirited music has enjoyed a renaissance. Concerts showcased his work from Potsdam to Tallahassee, and a museum to his life opened in his adoptive city of Hamburg. In the German town of Frankfurt an der Oder, right on the Polish border and where CPE studied law before becoming a full-time musician, visitors can find both a concert hall and a street name honouring him.

Thanks to a steady stream of album releases, including some by the finest contemporary performers, CPE Bach has surely now emerged from behind his sneering sceptics. He hasn’t quite surpassed his own father just yet – a skilled and inventive composer he undoubtedly was, few music lovers would today accord Carl Philipp Emanuel Bach the same magical status as Johann Sebastian. But as the young Bach’s undulating star shows so vividly, fame is mercurial, and it can sometimes take lifetimes to learn how you’ll truly be remembered.