The German title ‘Fantasie’ comes from an era in which the word ‘improvisation’ did not exist, but the practice was taken for granted if you were a professional musician. The musical meaning of the verb fantasieren is ‘to improvise’. Therefore the sense of improvisation permeates every part of this short, wonderful work.

I would approach this piece with an improvisational state of mind, the existence of which has been recently recognised by neuroscientists, following experiments involving improvising musicians and audiences in live concerts. The Fantasy offers numerous opportunities for extemporisation, notably at the end. The last 10 bars as printed were added by a publisher, but Mozart had left this part (bar 97 onwards) deliberately blank, allowing the performer to improvise a conclusion.

The opening of the Fantasy (bars 1-9) invites us to sculpt the music freely through time: we don’t want it to sound remotely metronomic. Although the harmonic rhythm suggests alla breve (two in a bar), Mozart slurs the figuration into groups of uneven length, which already breaks through the idea of common symmetry.

Next, look at the voice-leading in the inner parts and let that shape the direction of the longer phrases. Underneath the surface (the ‘foreground’ in Schenkerian terms), there is a deeper layer that holds the music together both horizontally and harmonically. Try to be aware of this underlying background structure as a dynamic and long-term expressive factor (through tension-release relations and directionality towards goal-points), which will also form the basis over which we can add judicious improvisation later in the piece.

For the Adagio section (from bar 12), in principle we usually don’t improvise the first time a melody or motif appears. Save that for the repetition of a phrase, and then do not play it the same way twice – just as you would not use the same words and the same intonation in speech when you find it necessary to repeat an element of a story. In this theme, the pace, dynamics and shaping of the left hand are driven by the natural decay of the melody’s long first note, the double-dotted F: the left hand’s three chords should form a diminuendo so that the F can keep singing above them despite its inevitable fading. The two hands also do not need to play religiously together. Broadly speaking, the left hand sets the pulse and harmonic rhythm, giving the right hand the chance to sing with more freedom.

The appoggiaturas (for example, the G to F, bar 12, third crochet beat) can be used to increase the music’s sense of anguish, adding to its wider emotional charge. The harmonic progressions on the descending chromatic bass line in bars 20-22 travel towards the pause on the fourth beat of bar 22, which you can take as an implied fermata. Incidentally, ignore the bar lines! Artur Schnabel used to say that bar lines are like a shoebox; they contain the music, but they do not constitute the music.

In bars 22-28, the rests that punctuate these brief right-hand motifs provide a feeling of breathlessness. While the right-hand figure presses forwards, making the impression of one in a bar (note the single harmonic degree per bar), the left hand’s dynamics between the second and third chords (the two quavers of the second crochet beat) conversely can retreat slightly. When you reach the top appoggiatura (bar 33) there is not one right or wrong way to articulate its emphasis: it depends how you choose to build up the whole phrase, of which this is the ultimate goal-point.

The first flourish (bar 34) begins with the semiquaver rest, which is hugely important. Feel it like an intake of breath – and if you slightly extend the last top E flat on the diminished seventh, that logically suggests the resolution on to G minor in the next bar – E flat is the appoggiatura of the dominant of G minor (D). The second flourish (bar 44) is larger, a free-flowing, ‘unmeasured’ mini-cadenza; many musicologists would describe it as a written-out improvisation. You can shape your own sub-phrases within it, leaning on up‑beats as launch pads.

Now the D minor melody returns and this time there is room for improvising variants and embellishments, since we have already heard the original. One principle is that if you are free with your ideas in the first part of the phrase (bar 45), you balance that by not embellishing too intensely in the second part (bar 46). Try improvising gestures that point towards the C sharp (or the D sharp to E) in bar 46 as the motif’s goal-point; then elaborate less in the ensuing bar. I would suggest practising by experimenting with several different progressions between the departure point and the goal-point. The forte (bar 49) is not marked subito, but one could interpret it as sudden, and if so, emphasise it by, for instance, adding an appoggiatura.

When we reach the D major Allegretto, the spirit changes to dolce – sweet or gentle – with a livelier 2/4 instead of 4/4 metre. Here, remember that there is no such thing as a ‘copy-and-paste’ repeat: if you were telling the same part of a story again, it would be for a good narrative-related reason, so you would not use the same words. Likewise, here, on the repeat (bars 63-69), improvise freely with the melodic line, but without changing any of the music’s underlying harmonic progressions. Try practising the harmonic reduction alone, to create in your ear a foundation as large as possible on which to add improvisations around the melody.

There’s no repeat sign on the next part, from bar 70, but the music is repeated nonetheless, so, again, don’t ‘copy and paste’ it the second time (bars 78-82); you could extemporise a decoration instead. I would never recommend to my students that they prepare anything in a fixed way and I myself try not to fall back on anything that feels too ‘safe’ in a concert. The idea is to include a risk-taking element, share it with your audience, and enjoy it! Try also to balance out any wilder improvisation – the lack of stability when the music demands it – with something much more stable.

The Fantasy’s printed conclusion, that ‘happy ever after’ ending, is – as we’ve noted – not by Mozart, but by a frustrated editor who needed a finished work in order to sell copies. It consists of 10 banal, uninspired bars and there is no trace of it in the manuscript. It is also quite misleading: if you look at other fantasias, you will see that it is usual for the music to bring back the opening ideas, which here would be much less cheerful. Aesthetically, this final improvisation’s aim is to return to the world in which the piece began, bringing it the unity of time and space. Mozart often does this, coming back from somewhere very distant, even after he has torn the world apart on the way.

As this is a relatively short piece, a brief coda might be appropriate. But the opposite logic also makes sense: we could improvise a more substantial coda, giving the Fantasy an ABA structure. That choice is for each musician to decide for themselves. I believe in trying the second option, so that you can dive back into the main message of the Fantasy, which is not far from the world of the D minor String Quartet (K421), the Requiem or some of Mozart’s concerto slow movements.

How to start this coda? After the dramatic chords (bars 95-97), surprise yourself. Set a challenge by disrupting the cadence. Go from the dominant chord not to the predictable tonic, but to something else: perhaps an interrupted cadence, or a switch to the minor, or something still more extreme (a diminished chord) that will allow you to travel anywhere except back to D major and will let you modulate gradually towards D minor.

Finally, be aware of your timeline when improvising in a piece like this. If an improvised part goes on for too long, it risks overbalancing the work’s architecture. The same is true when improvising a cadenza in a concerto; you don’t want it to seem self-indulgent. It’s possible, with practice, to internalise the sense of how it feels to play for about one minute. Once you have assimilated this sensation, then within the sense of balanced structure you can engage in your storytelling with fantasy and enjoyment. 

This masterclass and the sheet music for Mozart's Fantasy in D minor, K397 appears in the November 2023 of International Piano. Subscribe today