At the conservatoria, I often encounter singers and conductors arguing that the major third should be intonated low. The reasoning behind this claim is as follows. Modern instruments are tuned according to the equal temperament. In that system the major third is higher than the just third according to the overtones. That is, a just third a lower than the equal temperament third. And – according to this line of thought – a just third is ‘more natural’ than an equal tempered third and it sounds purer and better. Thus, the conclusion is that major thirds should be intonated low. In the same train of thought we should intonate minor thirds high.

However, I would like to make a couple of comments at this way of reasoning:

  • If a choir is singing with accompaniment and the instruments are equally tempered, this will result in a difference between the intonation of the choir and the accompaniment. And surely that is not the intention. Thus, the intonation should definitely depend on the kind of instruments that play along.
  • The equal temperament has made it possible to use all keys. A lot of music of the last century, both classical and pop and jazz, is harmonically complex and this has occurred precisely because of the equal temperament. It seem strange to use just intonation in these modern music styles. That wouldn’t fit the styles and, in the modulations, strange illogical situations would occur in the enharmonic tones.
  • Furthermore, for the modern music styles, we might turn the reasoning around. The music demands for equal temperament. But in real life we are hearing just intonation all the time. (A single sounding snare gives rise to upper tones, as well as lots of machines like a vacuum cleaner.) Because of all those influences we tend to sing just thirds instead of equally tempered thirds. Thus, we should intonate major third high.
  • The difference between just thirds and equal tempered thirds is really small. Only well-trained musicians can hear the difference. And only a few singers are capable of making the difference audible using their voice. Therefore, the difference between just and well-tempered is mainly theoretical. In reality, only few singers know how to deal with it.
  • And here is one more important point. For amateur choirs going flat is a big problem. Somehow singers tend to be low in intonation rather than being high. In my view, it’s bad advice to ask for low intonation on major thirds. Chances are that the thirds will be intonated too low (even for the just temperament). The probability of the choir going flat will be even greater and in the end the music will only sound less beautiful.

All in all, I think aiming for low major thirds might play a role in highly-trained choirs singing ancient music, either a cappella or with old instruments. But it remains to be seen whether in other situations this is a good way to go about.

It would be interesting to investigate intonation of good string quartets. Do they favour just intonation? Do they intonate in a different manner as soon as an (equally tempered) piano is playing along? Do they intonate modern music differently than Haydn and Mozart?