stable verses unstable notes and chords

[WaterGuy]

Hello. I'm new to music theory and am interested in knowing more about a topic hinted at in a couple of Guni's (well-written, BTW) articles: stability.

From Guni's article on solfege, I've inferred that the root, major third and perfect fifth are "stable notes" and other notes resolve to them, making the other notes essentially "unstable." This sort of makes sense to me as the major triad is the first building block of western music. Is this correct? If so, why are certain notes stable, and others not? Also, are some notes more unstable than others? Guni alluded to a tension curve, what is that?

In Guni's triad article, he lists out different chords of various stability. How do you rate the stability of a chord? Is it based on how the notes in the chord relate to the parent key? Is there a preference for the position within the chord for determining a chord's stability? For example, the V chord is built from P5, M7 and M2 of the key, so by my recogning, it would be stable, unstable, unstable. But the mII chord would be built from the M2, P4 and M6 of the key, so wouldn't that be less stable than the V chord? What am I missing here?

Thanks for any and all help.

[Bongo Boy]

...from my theory book:

DO, MI and SO [I, iii, V] are considered the resting or 'resolved' tones of the major scale.
RE and LA [ii, vi] are considered mildly active as they are resolved by a whole step.
FA and TI [IV, vii] are considered very active as they resolve by a half step.

And in terms of resolutions:

The main active-to-resting resolutions occuring within the major scale are:

RE down to DO (by whole step)
FA down to MI (by half step)
LA down to SO (by whole step)
TI up to DO (by half step)

Of the above resolutions, FA-MI and TI-DO are arguably the most important as FA and TI are the most active scale degrees within the major scale, and these resolutions are via the strong and leading half-step interval.

from Contemporary Music Theory Level Two by Mark Harrison, p.21 (Hal Leonard Publications). Hope this helps

[szulc]

The wwhwwwh construction or the major scale casues severalof things to happen.
1. The root becmes the ultimate resting point.
2. The third becomes the secondary resting point.
3. The fifth becomes the tertiary resting point.

The notes want to resolve to one of these tones.
Or rather your ear is used to hearing the notes resolve to one of these tones.

Notes that are a half step away from a resting note have a stronger tonal magnetism than notes that are a whole step away from resting tones.
Resting tones have no tonal magnetism because they are stable.

The V chord has the notes 5 7 2
the ii chpord has the notes 2 4 6.
The pull of 7 to 1 is stronger than the pull of 4 to 3 so V sounds like it needs to resolve very strongly. V resolves to I and ii resolves to V which in of itself is unstable and needs to resolve to I.

[WaterGuy]

Thank you both. That was very helpful.

[Bongo Boy]

Also, you can write out a selected chord progression (using triads, for example) as vertical 'stacks', either as notes on a staff or as a stack of note names, and visually 'see' the movement between the tones. For example, a II-V-I in C:

Dmi7 - G7 - Cma7

F  F  E

C  B  B

D  G  C

Voiced this way, you can see the FA-FA-MI movement in the upper tone (F-F-E), and the DO-TI-TI movement in the middle tones (C-B-B). These are both semi-tone movements in the same key.

This is one way, at least, to start analysing why a given chord progression does what it does, and how it might help one determine key, etc. I'm can't apply this yet, myself, but it's one approach I'm using.