Mental Chord Organization/Classification

Check out this lesson:

Guide to Chord Formation.

This lesson, The Power of Three, covers the same basic material and may be a bit more accessible.

It doesn't explain how they are arrived at, but I've made a flash tool that's a quick reference guide to which diatonic chords are in a key, here. (You might want to download the Win or Mac standalone version if you're going to use it, as the site is hcanging hosts over the next couple of days... :roll:)

You've got some confusion here, because in organizing chords there are a number of different contexts you can use. Take the list you found on Wiki one by one... the first and third are ways of cataloging chords:

the number of pitch classes it contains tells you if a chord is a synonym of some other chord. The basis of pitch classes is integer notation - rather than declaring a note as the 'root', it assigns numbers to each pitch, typically using 0 for C, 1 for C#, etc. So if you have C6 (CEGA), you have tones 0,4,7,9... and you can see that's the exact same tones as Am7 (ACEG).

Since the numbers represent absolute pitches, you can't see similarities between C major (0, 4, 7) and D major (2, 6, 9). But the system can be refined...

Having assigned integers to pitches, you can then label the intervals by pitch class. Because an interval and its inversion use the same tones (a perfect fifth C-G is the same notes as a perfect fourth, G-C), you can use pitch class intervals - the integer differences between two tones - which will always be 6 or lower. For intervals above 6 half steps, you use the inversion. So our C6 chord has intervals 2, 3, 4, 5 - you have a pair of tones a major second apart (G-A), a pair of tones a minor third apart (E-G), a pair of tones a major third apart (C-E), and a pair of tones a perfect fourth apart (G-C). No matter how you look at the tones, these are the intervals you get: C-A = A-C, minor third, E-A = perfect fourth.

Pitch class intervals give you perhaps the most comprehensive comparison of chords, but the system is difficult to learn compared to the standard naming system.

its precise intervallic construction: for example, if it is a triad, is it major, minor, augmented or diminished? This is the system of organizing chords in everyday use. A chord's name tells you the arrangement of intervals that make it up: a major chord is a major third-minor third; a minor chord puts the minor third first, then the major third. The downside to interval construction is that it gives you the chord tones in root position; you have to re-arrange the tones to form inversions.

The other three aren't really useful for cataloging chords in isolation, but they have other uses. The second one on your list: the general type of intervals it contains: for example seconds, thirds, or fourths. tells you about the type of harmony used for constructing the chord: tertian harmony, secundal harmony, quartal harmony, etc. Almost all of the chords you'll run across are in tertian harmony - they're composed of thirds of some type. It doesn't matter of the chord is major, minor, dominant ninth, whatever - it's stacked thirds. Comparing chords by interval type is only useful when you're comparing different harmonic structures - for instance, contrasting the quartal harmonies of Chick Corea to the tertian harmonies of the standard pop tune.

The fourth item gives you information about the use of the chord in a composition, rather than information about the chord itself: the scale degree of the root note or bass note In order to figure out what degree you're on, you need to know the key you happen to be in. Without the context of key, this method is irrelevant. F major is F major, whether it's the I in F, the IV in C, the III in D minor, etc.

The last one, whether the chord is inverted in register, tells you only information about the voicing - that is, differences between the tones in two of the same chord. You can spell C major CEG or EGC; inversions deal with that difference. The inversion doesn't matter that much when you're comparing two different chords - B7 in first inversion bears little resemblance to Ebm in first inversion.

Thanks :) , I'm really trying to learn all aspects of theory completely from the ground up, and have been doing well so far but things like chords have so many variables its hard to see how they all relate to each other. I'm will spend time to study more in depth tommorow to make sure if I really understand those parameters before I properly reply.

In the meantime, do most people learn from the opposite angle? By first familiarizing onself with most frequent chords in a musical genre (rock,metal,blues,country) and from there, using another chord theory to find the next transition? Since there seems to no finite way to break them down into solid groups, is this just one aspect of music that needs to be attacked from both sides at once to really see the connection? For example finding out that ones pref. genre uses say, 90% these 15-20 chords, from there using those chords as roots to find nice melodies and progressions for a song, and when problems arise use theory to fill in the gaps?

Is there some place online that lists some statistics or breakdowns of common genres, in terms of what %, among other things, chords are used? As I remember, from where I forget, the number was really quite small and for music like rock/metal were 90% power chords, which seems very limited. When I have time perhaps searching through tabs from songs I like and learning what chords are used would help. Sorry I seem to have just rambled on, while I will not limit my knowledge to the most popular chords perhaps there is method in viewing from the song> theory instead of vice versa?

I wouldn't try to go from generalizations in genres.

I explain music to my students as a language - the notes are like letters. Letters combine to form different words, like notes combine to form chords. You can put chords together to make progressions, musical sentences.

Like language has verbs to describe actions, we have sounds that are active - some of these sounds are very dissonant, some less so. But the action sounds can't work alone, like verbs can't work without nouns. You don't end a song with these 'action' chords - the dominant 7ths, their extensions, their alterations, and the augmented and diminished chords.

Nouns can stand alone. If I say the verb 'stealing', you - the listener - are left with questions. Who's stealing? What's being stolen? etc.

If I say a noun like 'car', you have a mental image. It's a story in itself, even if it's a boring one. Chords that are stable can stand alone, like nouns. These are the major and minor chords and their extensions.

Those are really the two basic categories - active chord sounds and passive chord sounds. Put them together - 'stealing cars' - and you have a story. An image and an action... a basic plot line. All chord progressions succeed by mixing stable and unstable sounds.

There are dozens of ways you can categorize chords, but that's the simplest starting point I know - is the sound active or passive? Could I stop right now and be satisfied, or does that last chord demand something more?

Once you get the active/passive tension/release concept down for chord groupings, all of the rest - no matter what categories you choose - are just refinements.