Playing pieces in time is one of the hardest skills a musician has to master, if they haven't learnt to do it correctly from the outset. You only need to watch a conductor beat time to realise that it's not as straightforward as it seems! When you learn new repertoire, or want to correct an existing piece, one of the most important things you must be able to do is keep a steady tempo. Too often when we play we rely on our own internal rhythm, and are unaware of when we are speeding up or slowing down. Practicing with a metronome, which I've written about before, can be a useful first step to putting this right.

Once your fingers are sure of the notes, pick out whatever you consider to be the hardest part of the piece you're working on and set your metronome to a very slow speed (that is, sixty beats a minute or less). If you can't maintain a steady tempo at your initial speed, reduce it even further. Then, when you feel confident that you are staying in time, slowly increase the tempo in small steps. It can also be helpful to vary what each tick of the metronome represents, for instance a half beat or quarter beat (though I recommend you start with whole beats). A tick might also represent two beats on occasion, or even four.

Difficult rhythms, compound time and irregular note groupings can be practiced in a similar way, but you must always be clear about the main beats and accentuations. Beats can be divided into smaller divisions, too. Instead of counting three quavers in a bar, for example, you could count six semiquavers before building up to larger divisions (counting 'one and two and three and' if appropriate). For younger children I find words are more effective than numbers, and often substitute apples for quavers and pears for crotchets! It also helps to tap rhythms out before you play them, especially complicated polyrhythms.

To become more comfortable with irregular note groupings (that is to say notes which are grouped in fives, sevens or nines as opposed to twos, threes or fours etc.), try the following exercise. Let's say you have to play five notes per beat, and the time signature is four crotchets beats per bar. Set the metronome to a slow speed, and count 1-2-3-4. Then break into pairs (1-2, 2-2, 3-2, 4-2), stressing the numbers in bold type and keeping them perfectly in time with the metronome. Next count in threes (1-2-3, 2-2-3, 3-2-3, 4-2-3), and so on until you arrive at 1-2-3-4-5, 2-2-3-4-5, 3-2-3-4-5, 4-2-3-4-5.

Once you've mastered using the metronome, try playing without it and see whether you're still in time. Counting out loud is an essential means of improving your timing (as opposed to counting in your head, which I've always found far less effective). The point is to achieve reliance on your 'internal' metronome, and by counting out loud you should be able to hear more clearly whether you are playing in time. Only then is it safe to count in your head, but every so often it's still a good idea to play to the metronome. While you don't want to be a slave to it, keeping strict time is a crucial discipline for all musicians.

In Theory, In Practice

Once you're able to maintain strict time, you will be able to introduce changes of tempo into your playing. Rubato (from the Italian tempo rubato, meaning 'robbed' or 'borrowed' time) alters the relationship between written note values by making the established pulse flexible. The term is largely associated with the nineteenth century, but it can be traced as far back as Frescobaldi's liturgical organ pieces Fiori Musicali (Musical Flowers, 1635). Composers from the Baroque to the present day have expected performers to use rubato, and it is as prevalent in popular, jazz and folk music as it is in classical music.

For pianists the technique really came to prominence with the works of Chopin, where changes in tempo are made freely without the need to compensate for lost time. The original tempo is simply resumed at the performer's discretion. In his book Tempo Rubato and Other Essays, Constantin von Sternberg observed: 'There are those who believe the use of rubato begins with Chopin, and that it must not be employed in any music written before him. Then there are arch-pedants who insist rubato not only begins but ends with Chopin. This is, of course, pure cant, the bulwark of ignorance and bigotry.'

Unlike some of the more straightforward elements of playing the piano, rubato is instinctive. To describe it in words (and, indeed, to explain how to do it) is extremely difficult. Franz Liszt once said to a pupil: "Look at these trees. The wind plays in the leaves and stirs up life among them, but the tree remains the same. That is Chopinesque rubato." As the great Maurizio Pollini wrote: 'Rubato must emerge spontaneously. It cannot be calculated, but must be totally free. It's not even something you can teach: each performer must feel it on the basis of his or her own sensitivity. There's no magic formula.'

Pollini was, of course, quite right. The extent to which rubato is used will depend upon the stylistic and musical context, and the preferences of the performer. Rubato should convert energy into languor and steadiness into capriciousness, and if the principles are understood it can be quite inspirational to leave the precise execution to chance, mood and whim. From the listener's perspective, the acid test is whether it is possible to sing along. If you can hold on to a melodic line, and conduct a performance without feeling that your conducting is losing its smoothness and natural ease, the rubato has musical integrity.

Accelerandos and ritenutos are both used in the execution of rubato, particularly at cadence points, in order to heighten the performer's expressive powers of interpretation. There's no shortage of material that you can use to begin developing your sense of rhythmic freedom. Burgmüller's 25 Easy and Progressive Studies and 18 Characteristic Studies are full of varied tempo markings, and for more advanced players I would recommend Grieg's Arietta from the Lyric Pieces, Debussy's ever-popular Claire de Lune from the Suite bergamasque and Chopin's Berceuse (Cradle Song).

Subtle Fluctuations

It's easy to see how rubato can be added to the celebrated Berceuse, with its continuous and hypnotic left hand rhythmic ostinato. Between those left hand quaver figurations the right hand weaves an exquisite, quasi-improvisatory melody. The scope for adjusting pace and colour in this melody is almost infinite and should, ideally, be spontaneous. Subtle rubato is possible in the left hand too, in which case it will follow the right hand's phrasing and take its cue from the musical climaxes within the piece. (Some musicians actually think of their pieces as waves, gently ebbing and flowing in a series of climaxes.)

While sensitive rubato is required for the phrasing of the Berceuse, a good example of a more exaggerated approach would be Rubinstein's 1946 recording of the first Piano Concerto (RCA Victor LM-1810). Both of the Chopin concertos are challenging to conduct if the soloist adopts a wayward, angular rubato. But if flexibility is used with logic and sensitivity, as is the case with Rubinstein, the music is never routine. Incidentally, I also recommend his recordings of the nocturnes from the 1960s. The mastery of tone and unerring sense of rubato make these among his greatest recordings, in my opinion.

Recordings are helpful, because it's important to be aware of what rubato can sound like before attempting changes in tempo yourself. So perhaps taking one of the nocturnes as your starting point, make a bar-by-bar comparison of different pianists' approaches. Listen carefully to the left hand (the conductor), and observe how the irregular note groupings of the right hand (the soloist) fit in. Does the music sound mathematical or musical? Does the pulse quicken in a particular bar, or slow down? Once you've got the basic concept, feeling rubato should be much easier. Though be sure your pulse is secure before changing it.

I often play along when introducing rubato, to help students feel the bending of the rhythm. I also play the left hand part in strict time sometimes, while they experiment with rubato in the melody. It's important to experiment as rubato can affect both melody and accompaniment, as with the Berceuse, or just the melody. (Think of how a jazz combo works: the bass and drum players use repetition to fix the structure of the piece, while the sax player improvises around them. And in Baroque music, the florid passacaglia variations that give performers so much freedom can be thought of as 'notated rubato'.)

Whatever techniques a teacher uses, rubato is hard to teach. Do you want to linger slightly on this note? Should you slow down towards the end of that phrase, or get a little quicker? Like so many things musical, you ultimately have to develop and rely on a sensitive ear. Although the written score will provide some clues, it's more often than not your ear that will direct you towards the most successful musical solution. Never be afraid to use your discretion: experiment, and see what happens! Rubato is an extremely versatile tool, and will enhance the pleasure of any pianist who takes the time and trouble to master it.