The bluesy idiom of Kahane’s final variation has something in common with the mazurkas of Frédéric Chopin (1810-1849), in that both demand expressive rhythmical subtleties that simply can’t be captured in notation – they have to be felt.

The mazurka, a lively folk dance in triple time with a syncopated first beat, originated in the Mazovia province of northern Poland. Of the several dance forms Chopin employed (the waltz and polonaise among them), the mazurka was used most often. He wrote 50 of them across the entire duration of his career, and his progress as a musician can be heard in their variety.

The three mazurkas we hear tonight all date from the middle period of Chopin’s short life. The Mazurka in B-flat minor, Op. 24, No. 4, was published in 1835, the Mazurka in C-sharp minor, Op. 50, No. 3, in 1841, and the Mazurka in C minor, Op. 56, No. 3, in 1844. All three are examples of how far Chopin has taken the initial inspiration of a vigorous dance and transformed it into a supple emotional catalyst. It is an unfair simplification to evoke veiled salons when discussing some of Chopin’s achievements, but there is an unavoidable urge to compare this music, with its instant changes in mood, to the flicker and blaze of candle flame.

“I should like now to finish my violoncello sonata, barcarolle and something else I don’t know how to name,” wrote Chopin in a letter of December 1845. Working through debilitating illness and the grinding conclusion of his unhappy relationship with the writer George Sand, Chopin published in the following summer his Barcarolle, Op. 60 and the “something else” known eventually as the Polonaise-Fantasie, Op. 61 – consecutive towering masterpieces of his final years.

Drawn from two Italian words, barca or boat, and rollo or rower, the barcarolle was a beloved 19th-century cliché: the gently rocking romantic songs of Venetian gondoliers. Chopin’s Barcarolle is anything but that. Working with a broad 12/8 time signature, Chopin’s watery undulations begin calmly, but upon their return in the final third of the piece, build like the immense swells of the open ocean – no moonlit canal scene here, but a relentless and dramatic escalation.

In much the same way that his Barcarolle pulverizes the conventions of a lulling boat-song, Chopin’s Polonaise-Fantasie vaults over any expectations we have of the polonaise form he had popularized throughout his career. In fact, it has long been observed that it is far more a fantasy than a polonaise.

The mysterious and wandering opening, radically unconventional, anticipates the later experiments of Wagner and Liszt. And those moments when the martial triple meter of the traditional polonaise is heard, serve more as demarcations of episodes, rather than structural foundations. No, the greatness of the piece lies in its embrace of fantasy and the possibility of moving, in a musical flash, from melancholy and rumination to triumph and ecstasy.