What determines the function of a chord?

Question

I’ve been trying to learn about functional harmony and I keep asking myself the above question. Each chord seems to have a general function (with exceptions) within scales, but why is that so? Were scales made with those functions in mind, or were those functions agreed upon or discovered after scales were already determined? Is it a result of having 7 notes in a scale? For example, if you were to choose 7 random notes within an octave...would the 5th chord always serve a dominant function?

DISCLAIMER: I know I’m asking a simple question that doesn’t have a simple answer and I don’t expect any response to be cut and dry. I also realize I’m making a lot of assumptions about the way music works that may or may not be true, however any insight at all would be helpful! Thanks!

Answer 1

The chord root's relation to the tonic.

You can expand that to say: the relationship of tones to the tonic and tonic chord.

The idea of function is definitely something that was developed long, long after scales and harmony developed over the ages.

Try to get away from the idea that chords come from a fixed scale. The only thing that is pretty well immutable are the tonic, subdominant, and dominant tones. The other tones can vary. Basic harmony is triads built on the different tones.

In a way you can say that function does not care about any particular scale. It some ways function is ambivalent about mode/chord quality except that a proper dominant is major chord. The tonic and subdominant chords can be either major or minor. You can mix those qualities around without destroying function.

So you could have G major go to C major, or G major go to C minor. Both fulfill the function of a dominant moving to a tonic. You can say those chords come from this or that scale, but it makes no difference to function.

This point is most easily demonstrated in minor key music where the tonic, subdominant, and dominant chord often change between major or minor quality as the music unfolds. You need 10 tones just to account for those three function and the possible chords! Clearly that goes beyond a 7 tone, diatonic scale.

Answer 2

At the highest level, the why is because traditional western music is goal oriented. The goal in this case is to resolve to tonic, or I. How you get to that goal is your chord progressions. Within that progression there are lots of rules but the basic idea is only certain combinations of chords go together. As @michael-curtis said you can have G-C, which is V-I, a very common cadence.

Were the scales made with that in mind? I'm not a music history expert here (I can hear my music history professor's voice now) but my understanding is that it evolved over time. If you look at early Medieval music, which is in modes, it doesn't really have chords, and the tunings were very different and written mostly for voice and smaller ensembles. Same with ancient Greek music, which our system is based on.

As instruments and tunings evolved more things became possible and chords and larger ensembles became more common, basically more notes at one time. Medieval music of course also had its own sense of progression and cadence (resolution) and as music became more complex this idea of progression became more complex. In terms of multiple notes sounded at the same time, it progressed from just literally being coincidental to having to fit inside a chord. So instead of going from single note G-C pieces would go from V-I or G-B-D-F > C-E-G so that each note in the G7 chord resolves into the C chord and all notes that are sounding, regardless of how many, fit inside this structure and function.

Also at some point music started to gravitate from modes to the 2 scales major (ionian mode) and natural minor (aeolian mode) which account for all 24 traditional major minor keys. I think the big shift here is that what became the most popular was vii-I, or ti-do, a half step rather than a whole step which is a stronger resolution. This is present in both major and minor because you always raise the seventh scale degree in minor to resolve back to i (harmonic minor, not to mention melodic minor).

Answer 3

So many questions..! A long time ago (once upon a time...) music was somewhat simpler, at a time when modes ruled, as already stated.

Over time, the modes gradually morphed, in the Western world, to what we use today. The diatonic notes which fit together to make the scales we use. Even some of those notes have been re-tuned to fit into how we use them better.See 12tet.

So, we have a set (or several sets) of notes. Consider first the set that makes up our major scale - the Ionian mode. play up and down and sideways, and one note in particular, for most people, seems to be slightly more prominent - one which most of us would be happy to say yes, the tune could stop there, on that, and it would feel like it's finished. That's the root, the tonic, number one.

By adding extra notes to the root, we quickly find that there are two more which cement that feeling even more. 3 and 5 namely. The root triad. Try as many other combinations as you like, and no other comes closer. In fact, some come farther away!

Try the one using 5,7,and 9. In key C, that's G B D. Most listeners get the feeling that this creates a pull back to the tonic. So much so, it's called the dominant - pushy, if you like. One reason we give for that is that, like electricity, music often tries to take the path of least resistance. Thus, the B in that dominant chord wants to go the shortest way to root - one semitone. Put an F into the mix, making the chord G7, and that again is happy to go one semitone to E, which is a key part of that root chord.

That's it for now!