what does it mean for one chord to gravitate to another?

[kevin69]

When taking about chord progressions such as I-ii-V-I people talk about I being 'stable',
ii gravitating towards V, and V gravitating towards I.

I can't hear this: ii-V sounds pretty much as natural as V-ii to me.

What should i be listening for in a I-ii-V-I progression that i won't hear in a I-V-ii-I progression?
Or can someone explain what this means in some other way?

[theholygideons]

It all has to do with the overtone series, where any note can be contained within the corresponding sub-dominant above. So therefore, there is a tendency for the ear to perceive a gravitating from ii to V, and then V to I, through the upward ascension of sub-dominants, where the root degrees give up their sovereignty and appear as higher overtones in the next chord. Whereas if you were to play I-V-ii-I, then the progression would appear weak, because it acts as a descending progression where, for example, the root of the ii chord is already apparent in the fifth of the V chord, so there is no natural tendency to go from V-ii, rather the other way around, ii-V. I hope this makes sense...it's what i recall from reading theory of harmony by Arnold Schoenberg, which i'm only half way through.

Perhaps someone else could simplify or further clarify my explanation?   

[ted]

I read about this with interest, as I have missed the bus with it all my life. I cannot feel that a given chord is "going" anywhere in particular, or "ought to" be followed by anything special. I can do it at the intellectual level, of course, I can follow and remember a pattern, a set of instructions, the "what" so to speak, but have never perceived the "why" of it in any strong aural sense.

[kevin69]

thank you for that, I think i see:

In ii-V-I (with triads), each root note is echoed in the harmonics of the following chord: this links the chords together aurally. The root note is 'new' each time, and so sounds strong.

In I-V-ii (with triads), the root is sounded in the preceding chord, so the chords are linked aurally, but because we've already heard the root already it sounds weak. You might say that the root loses the element of surprise.

I'm not sure i could pick this out by ear (yet) but at least i now know what i'm listening for

thanks again
kevin