What is tonality when you're not playing with a diatonic scale?

Question

Is there any definition of tonality which generalizes beyond a diatonic scale? For instance, can you have resolution from a dominant to a tonic if you're only using a pentatonic scale? Clearly you can't just say a dominant is the chord rooted on the 5th scale degree for every scale, when in each scale "5" will mean something else. I have read that even using a whole tone scale in Voiles Debussy was able to maintain a distinction between dominant and tonic, but I'm not sure exactly what that means.

Thanks!

Answer 1

Tonality doesn't really need any particular scale or harmonies. It mostly needs one thing: one note that feels like home. In many genres around the world, such a “home” is simply established with an all-underlying drone note, and all melody/harmony is developed around the overtones of that drone. In e.g. Indian music, this involves lots of notes that don't even exist in Western scales. Still there can be no doubt what would be the tonic, if you called it thus.

Pentatonic scales are in fact very often used in drone-based folk music. The most obvious examples are bagpipe or hurdy-gurdy tunes.

And (as alephzero already commented) if you do use harmonies, then there are lots of ways that clearly point to a tonic without using any dominant in the classical sense. The most common alternative is the plagal cadence Ⅳ-Ⅰ, which is quite common across pop/rock/country, again indeed often in connection with pentatonic scales.

Answer 2

I offer not a complete answer, but rather counter assertion: that key (tonality) is cultural. By way of argument i offer this just-so story told by one of my composition teachers:

During WWII René Leibowitz befriended a Moroccan living in the Free French territories. After the war, he invited this Moroccan friend to attend a concert in Paris where he was conducting. Knowing that this friend had limited art music experience, the performance that Leibowitz invited his friend to was of Beethoven 5. After the performance Leibowitz asked his friend what he thought of this example of European Art Music. "It was wonderful!" came the reply, "but why did it end on the wrong note?"

What this story demonstrates (along with Western, colonialist chauvinism) is that not even 8 perfect cadences in C in a row followed by 30-odd bars of C major chords will guarantee that your audience will hear C as the home key if their musical vocabulary is sufficiently different!

Additionally, i would posit that equally important as root movement to the feeling of harmonic motion, & by extension key, is the melodic movement of tendency tones. The motion 7→8, 2→1, 4→3, 6→5 all tend to reinforce the primacy of the tonic (or the tonic harmony) in the Western tradition. So your non-diatonic scale can leverage these tendency tones — in fact it could set up its own tendency tones (e.g. Poulenc & Bartok were fond of ♭2→1) — to build its own sense of key regardless of the chordal structures availed by the scale. In an example like Debussy's works exploiting modes of limited transposition like the whole-tone scale, this melodic movement, as well as the semi-tone offset relationship of the whole-tone scales (which is also an offset of a perfect 5th), can be exploited by a skilled composer in the Western tradition to give the impression of "tonic" & "dominant" harmonic regions despite the lack of harmonic motion in the whole-tone scale itself.

Answer 3

The general term for this is non-functional harmony. The term's meaning is fairly obvious if you understand the antonym: It means that the harmony does not readily (or usefully, if you prefer) match with functional harmonic descriptors, like "dominant", that are based more or less on the roles that chords play in diatonic scales or those that highly resemble diatonic scales, like the harmonic and melodic minor.

Truthfully, you are going to have a hard time finding a satisfying answer to your question as stated, because tonality outside of diatonic systems (non-functional harmony) is much more difficult to define than tonality within it, and oftentimes you're going to have to look into the theory of the idiom you're analyzing to find a sufficient answer to this question. The major pentatonic scale is a great example of this, and you touched on the problem: What use is there calling the fifth the dominant interval when you can't even form a dominant chord on it? The fact is that you can't really create a strong cadence out of the major pentatonic scale because there's no tritone and no leading tone to the root, so you have to come up with different ways to describe the relationship between notes and chords formed out of the pentatonic scale than T-S-D. What functional tonality does tell you about the pentatonic scale is, as I mentioned above, that with those combination of notes you'll be unable to reproduce a perfect cadence and that therefore you can't create any strong tension-resolve contrasts like you can in the major scale (and other scales that can replicate the V7-I relationship). It is more complicated to do this kind of analysis with the whole tone scale because its relationship to diatonic harmony is considerably more complex, but it is possible. For example, using the whole tone scale built a semitone away from the root gives a collection of notes that strongly suggest the dominant (since you can form V7#5 with them, as well as its tritone sub if you're a jazz person).

To say that this is a deep rabbit hole is an understatement. For example, you can look at twelve-tone as being a total rejection of functional harmony specifically because it is impossible to ascertain any tonality from twelve pitches given roughly equal emphasis. There's also the diminished scale, which reveals a number of connections between chords that are otherwise very difficult to explain within the bounds of functional harmony.