When we learn a piece of music, we assume that choosing the right tempo is going to be one of the principal problems. However, when we really consider the question, we must admit that there can’t be such a thing as one 'right’ tempo (if there was, surely all the others would be wrong?). Some pieces are played at very different speeds by different people. Nevertheless we must go by the assumption that there are ways to determine what the right tempo is for us, a tempo where we feel we can express what is in the music in the best possible way, because the opposite assumption (namely that there aren’t ways to determine what the right tempo is for us) leads to crude and counterproductive relativism: twice as fast? Four times as slow? It doesn’t matter anymore. So what are the ways to determine the right tempo? Obviously, the indications (tempo indication, metre, metronome marks, etc) we are given are a guideline, but beyond that we have to look at the music itself. 

The simple answer? There are two possibilities. The first is basically what we are taught since childhood: to chose the right tempo, let’s look at the fastest and most complex passages. Doing that especially stops us from playing too fast in the beginning of a piece, guaranteeing that everything remains audible and intelligible later on. As an example, in the second movement of Bartók's Sonata for Solo Violin, he demands a slightly slower tempo when the subject of the fugue coexists with its inversion; here a higher degree of complexity equals a slower speed. This allows us to understand everything more clearly. 

The second possibility is to define the character, the mood of the piece, and adapt the speed to that. This happens much more often than we assume, it’s the reason many musicians speed up the very complex sections, because they are meant to be more agitated. In the same Bartók sonata, a section in the middle of the first movement has a slightly faster metronome than the rest of it, although it is clearly more dense and complex than the beginning. This way, we are assured of playing the music in the right character, even if some of the details become slightly blurred. 

Ultimately a good musician will do both of these things, because excluding one would surely lead to absurd results! It is absurd, for instance, to slow down the development section of the first movement of Brahms's Op 51 No 1 String Quartet just because it is more complex; the main feature of this movement is the ongoing rhythmic ostinato, it must keep going throughout. It would be equally absurd to speed up this section simply because it is more agitated, for the same reason. In Prokofiev’s First Violin Concerto, the Scherzo has no tempo changes, which means that a speed has to be found that can account for all the different characters (this is more difficult than it sounds); if the beginning is played too quickly, a couple of sections in the middle of the movement would have to be played considerably slower, which is not intended. There are countless other examples that would show each approach on its own to be lacking. The solution, then, is to use one approach to control the excesses of the other, so that we are guaranteed a result that is intelligible and in the right character. 

It's also important to realise that tempo indications such as metronome marks are useful, but not in themselves sufficient. In Anthèmes 1 for solo violin by Pierre Boulez, each section has a metronome mark; in Anthèmes 2 for violin and live electronics (which uses the same musical material but expands it), these metronome marks are altered, in some sections quite drastically. I was fortunate enough to have the chance to study Anthèmes with Pierre Boulez himself. He explained to me that the metronome markings are different in Anthèmes 2 because the music works at a different speed when it's actually played as opposed to when we're simply imagining it. It’s not that the tempos are actually different. 

What these approaches have in common is that the reference point is always the music itself, and not our gut feeling. It sounds obvious, but the tempo is essentially just the speed at which the music is played; so the question of how to chose the right tempo depends entirely on the content of the music. The answer in this case would be: if we understand and play the music correctly, we will automatically do so in the right tempo. 

Michael Barenboim’s new album of Bach, Bartók and Boulez is out now on Accentus Music.