What makes for a great chord? It depends on context and mood and purpose, obviously, but some generalizations can be made. In jazz, Tin Pan Alley, and Broadway music there’s a well-trodden trail of chord enrichment. You add the seventh note of the scale (as in blues) and then go on to add the ninth, perhaps the eleventh, conceivably even the thirteenth to color the base chord more and more with implied chords in neighboring keys. It’s like blending ingredients into an amazing French sauce. Here is the simplest version of the menu for enriching a C major chord:
BASIC CHORD NOTES
C (the 1st)
E (the 3rd)
G (the 5th)
PLUS……………………. IMPLYING ALSO THE CHORD OR KEY OF
Bb (the 7th)……………G minor
D (the 9th)………………………and Bb
F (the 11th)………………………………and D minor
A (the 13th)………………………………………and F
Popular music can accommodate complexity along these lines. It’s how the luxurious opening chord in “A Hard Day’s Night” is built up, for example. In art music, things can get weirder. For a chord that’s all suspense, impossible to assign to any home key yet mysteriously longing to belong somewhere, try the “Tristan chord” from Wagner’s Tristan and Isolde: F – B – D-sharp – G-sharp.
For a superchallenging chord with the strongest sweet-and-sour effect, try the “Petrushka chord” from Stravinsky’s ballet. All the notes of a C chord are combined with all the notes of the maximally dissonant F-sharp chord, like a demented C 15th.
If you long for just the sweetest and purest chord, I understand that, but an innocent C chord couldn’t be very impressive all by itself. It needs to be tied to something else so that when you hear it, you are stretched or caught in the collision between different positions in the music-world. Perhaps many would prefer to avoid Wagnerian or Stravinskian torture, but I think most of us enjoy a bit of a stretch, say between a C chord and an F chord nobly introducing it. Here you not only experience a nicely consonant layering of the remembered F onto the new C, you get a bit of a thrill in being suspended between two ways of construing the F-C relationship, either F as the fourth in the key of C or C as the fifth in the key of F. (If C dominates enough that you’re clear the F is meant to be the fourth of the C, the other possibility remains pleasantly on the edge of your awareness.)
Now let’s consider a song that starts in precisely this way, XTC’s “Another Satellite,” but then takes us on a journey to a much less common site of arrival.
[Spacing is correct on the main Hooks page]
…………..My heart is taken, it’s not lost in space
And I don’t want to see your moony moony face, I say
Why on earth do you revolve around me?
The E-flat chord sounds sweet-tartly good—tastes like cherries, I’d say—because it shifts us from C to the closely related key of E-flat, a key that uses the notes C minor would use, except it’s major. Keywise, it’s as though we’ve mounted up a level in a split-level house. True, we also dropped down to the E-flat chord from F, as though going to the seventh in the key of F, which involves the feeling of a spring pushed down that will come back up. And for yet another effect, the melody went from E-natural on “say” to E-flat on “why,” just a half step down, and changing keys while moving just slightly in pitch in the melody makes for a queasy feeling. But in any case the melody of “Why on,” E-flat B-flat, is squarely in the key of E-flat, just as the earlier notes had reinforced the key of C.
Next in the chord sequence, going down to A-flat (“earth”) from E-flat feels logical, as A-flat is the fourth in the key of E-flat. But since we only moved to E-flat a moment ago, we’re not all that firmly planted, and A-flat sounds so solid, so well supported by the melody, that we have to consider the possibility that it is our new key. Maybe yes, maybe no: we directly descend from A-flat to G-flat, which could be a move in the key of A-flat but could also simply be a routine whole-step chord change in some other key. The next change after that is another whole-step descent, from G-flat to F-flat:
Aren’t you aware of the . . .
At this point we don’t know what’s going on, keywise; we seem to be in a free-fall of descending chords. I wrote the chord as an F-flat because of the whole-step descent pattern we’ve been in. But we’ll have to construe the F-flat in retrospect as an E chord (the notes are the same) because the next change is to an A, most naturally heard as either the fourth of E or else the first for which E is the fifth:
gravity . . .
We’ve already taken some adventurous steps to get to this A chord, which hangs in the air of our quite possibly now being in the key of A. But the A is not (yet) our destination. Abruptly we are modulated back to the original home key of C with the help of a G, C’s fifth:
Don’t need another satellite
—and that should be the end. Yes, the return of C should mean the verse is over. And the melody here sounds like it did at the beginning. Uh-oh, the beginning . . . Now there’s a launch from C toward the strange true ending of the verse, a wild hair flying up over the last syllable of “satellite”:
We’ve pivoted on G again to go to A, which we once thought might be our destined home and maybe is after all. But it’s not the pure A we heard before. It’s got a fourth note added emphatically by the melody, not just as accompanying texture, and it’s not an ordinary fourth but a sharped (“augmented”) fourth, a D-sharp, which implies a B-major chord layered on top of the A-major chord for a very tangy polytonal effect—the auditory equivalent of double vision—and an exotic, dislocated sense of being “home” in the A. (Imagine going home one day and seeing palm trees sprouting out of your windows.) This is a possibility that you would find only on a much larger version of the jazz chord menu.
This A4aug wins my award for the greatest chord. We’ve approached it in an invigorating sequence of harmonic reorientations, and when we round the last corner we come upon it as a darkly radiant thing, a light beaming from deep space in the extended last syllable of “satellite.” Its unexpected D-sharp challenges us simultaneously as
(1) a flatted fifth in the A chord,
(2) a flatted third in our alternate home key of C major,
(3) the brash major third of the implied B chord on top of the A, and
(4) the first note of the E-flat that we took seriously as a home key possibility a few measures ago (for D-sharp is also E-flat).
In the event, this deftly prepared compound sounds like a cry of frustration and compassion: the one who is urgently pushing the satellite away knows that the satellite needs even more urgently not to be lost in the void.
 I mean a chord appreciated as having a remarkable chord-character, as opposed to simply a great chord-based event in a song (like the tremendous A major finishing each A-minor chorus of “She’s Not There,” or the always-strange-sounding jazzy Eb7 in a rube key of G that flits by at the start of each verse of “Fat Man In The Bathtub”).
 “Another Satellite” is actually a whole step lower than this, starting with an E-flat to B-flat change; but I wanted to stick with our friend C as the starting point.