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Note: This post requires a basic knowledge of intervals, which you can acquire by checking out my post Keith’s Crash Course On Intervals for Self-Taught Musicians. If you are not familiar with solfege syllables (do re mi fa sol), also read our Solfege Syllables To Intervals Translation chart.

This article comes as a response to a user question left in a comment on my article on modes. The question is:

Why (supposedly) can’t we hear Locrian mode?

Of all the seven modes derived from the major scale, Locrian is the only one considered to be a “theoretical mode”–one that our ears cannot actually hear. While there are supposed examples of Locrian mode, naysayers can argue that while these songs appear to be Locrian on paper, we hear them as a combination of chords borrowed from different parallel modes (”modal interchange”) or as being in a relative key.*

First, let’s explore what makes this particular tonality so interesting. Locrian is the only mode with a tritone interval and no perfect fifth (relative to the root note, not between the other notes of the key–in other words there is fi but no sol ^{[see solfege chart]}). This means that the root chord of a Locrian song is a diminished triad, which is comprised of the root, a minor third, and a tritone (the tritone would be called a diminished fifth in this context). It is this tritone that makes a diminished triad inherently unstable. While root chords are supposed to sound like a point of resolution or finality, tritones are so unstable that some say our ears can usually only hear them as going somewhere; we cannot hear a I diminished triad as ‘home.’

The most common place to find a tritone is in a V7 chord (V dominant 7), one of only a few seventh chords regularly used in classical music, and a chord which almost always resolves to I. The reason is because of its tritone. In my Intervals post, I explained that only intervals between the root and other notes are considered essential to a chord, not the relationships between the other notes. Tritones are the exception. This interval is so dissonant that it stands out in any context. The V7 has a tritone interval between its major 3rd and minor 7th. The major 3rd of a V7 chord will always be the leading tone (major 7th of the key or solfege syllable ti) and the minor 7th on the V7 chord will always be fa. When we listen to a V7 chord, our ears hear a strong pull from the leading tone up to solfege syllable do (root of the key) and from fa down to mi (major third of the key). Put do and mi together and you’ve got the I major chord.

Example: in the key of C major, a V7 chord is GBDF. B is both the major 3rd in this G7 chord and the leading tone of C major. F is the minor 7th and fa.

Technically speaking, there are several characteristics that are unique to a tritone. For one, it is the only interval which inverts to itself. For example, if you take the tritone interval from G to Db and flip it you get Db to G–another tritone. Secondly, it is the only interval which is not considered major, minor, or perfect. (It just is, man.) The tritone is in a league of its own.

Each of the 13 possible intervals are considered more stable (”consonant”) or less stable (”dissonant”). The tritone is one of the most dissonant. Played alone, a minor 2nd is more dissonant and jarring. This interval, like a tritone, is in neither the major (Ionian) nor minor (Aeolian) scales. In the context of a chord, however, a minor 2nd can sound quite pretty. In a major 7 chord, for example, the distance from the major 7th up to the root is a minor 2nd. But since we hear the major 7th interval going in the opposite direction, it sounds dissonant in a colorful way. Tritones always sound a little jarring to me (and yes, I’m including dominant chords). In the case of both intervals, our ear wants to hear perfect intervals (a unison and a perfect fifth, respectively), but they fall slightly short.

The latest pop song to come anywhere close to Locrian lately is Ciara’s “Like A Surgeon,” which features fi as the second bass note during the chorus (G in the key of C# minor). You could call this a borrowed chord (bVmaj7 from C# Lydian), but perhaps another brief flirtation with polytonality a la “Single Ladies” (both songs feature the writing and production of The-Dream and Christopher “Tricky” Stewart) because she sings minor 2nd (called a b9 tension in this context) over it, which is not considered an available tension on major 7 chords.

Most common examples of Locrian are riffs (short melodies which are repeated), not songs. The reasons why our ears tend to drift astray when hearing Locrian only apply to chords and harmony. Riffs are not like chords. They are more flexible. Because the notes are not occurring simultaneously (in the case of many rock riffs), our ear does not hear all of the same tendencies that intervals might suggest. All this being said, it’s hard not to hear YYZ as Locrian with the lead riff constantly reinforcing the root.