The locrian (or hyperaeolian) is the most useless of all the modes. The second and fifth intervals are flattened, allowing for neither a stable tonic chord nor a perfect cadence. Musical possibility itself seems to collapse when you lose these twin pillars. Without them, it becomes almost impossible to establish a tonal centre about which the music can organise.
Let me demonstrate with some music. Below is the first four bars of Mozart’s Piano Sonata No. 16, K545 (you’ll recognise it when you hear it). The original is in C major and will play first, after four bars which give the harmonic outline. Then the extract is repeated using the intervals of the locrian scale (2, 3, 5, 6, & 7 are flattened). Notice how harmonically unstable it has become, how the music seems to want to modulate, with no firm cadences to maintain a sense of the key.
Now, if I adapt it to the phrygian mode, perhaps the second weirdest mode, it still makes harmonic sense. Unlike the locrian the phrygian has a perfect fifth, allowing for a sense of resolution.
There are many examples of the phrygian mode. One can find it in Scarlatti’s keyboard sonatas owing to the Iberian influence (think Spanish guitar music), and also in Vaughan Williams’ Tallis Fantasia thanks to his interest in English folk music — to take but two examples.
But are there any pieces based on the locrian mode? I can’t think of any. Hindemith uses it quite a bit in the second movement of Symphonic Metamorphosis of Themes by Carl Maria von Weber, but he circumvents its harmonic problems by alternating between mixolydian (major scale with flattened seventh) and locrian.
The locrian, therefore, is more a theoretical invention than a practical one. Nevertheless, I thought I’d try to write a little piece in B locrian. It sounds pleasant enough — but that’s only because the piece keeps trying, against my will, to modulate away from B locrian towards a more satisfying key. Whenever I tried to reign it in, to bring the piece back to its supposed tonal centre, the result is completely inelegant. Music has preferences of its own, and it’s no use trying to overcome them.
Here is my ‘Fantasie’ in B locrian. I could think of no suitable titles. It was meant to be a galliard, but as well as losing track of the tonal centre, I also lost track of the metre! Still, all that aside, and excusing the audio quality, I rather like it. The locrian mode forces one to make some unusual harmonic choices, resulting in a kind of unsettled melancholy.