Sevenths
Wow, what a great and clearly stated Theory post. Very easy to understand. I'm sure many ukers are gonna get a lot out of it.
Indeed that was - and I'm sure they will! If I may, I'm going to add just a couple of observations on 7th chords that touch on some of the issues raised by yourself (and others) in the thread.
Firstly, as gvelasco so rightly says, you only need three notes to form a chord (your basic triad). Once you go on beyond 3 notes, you enter the realm of
extended chords (7ths first, but then, building on the '
every other number' principle, 9ths, 11ths & even 13ths also); but it's important to recognise that each successive combination of 3 notes in an extended chord forms a triad in its own right.
So when Uncle Rod talks about substituting a Dm7 for an F, effectively what he's doing is substituting a F/D (read as "
F over D" - F with a D in the bass) for a straight F. Let me explain:
If we begin counting out every other number starting on the D note, we get D, F, A - a Dm chord.
If we continue to the 7th of the Dm chord, we get D, F, A, C.
Those last 3 notes, F, A, C, together make up an F chord in their own right (sitting on top of that D)...
...and that's also why Dm7th sounds so much 'sweeter' than a straight Dm chord (as generally do all minor 7ths compared to their non-extended, triad, versions).
... and that's why Dm7 is so often such an effective substitution for F!
Now, let's take a look at G7 in the key of C.
It's formed from the notes of
G, B, D & F; but
B, D & F themselves comprise a chord in the key of C: the viiº chord - Bº (B-diminished). Diminished chords have a very unsettling quality to them. So if you think of G7 as being in effect Bº/G, you can understand why substituting a G7th chord for G in a chord progression gives that chord progression such a sense of
urgency. The chord progression suddenly wants to go somewhere else - and that somewhere is C...
Code:
G
Well I might take a train
G
I might take a plane,
G
but if I have to walk
G7
I'm gonna get there just the same
C G
I'm going to Kansas City, Kansas City here I come
Try playing those lines without ever going to the G7. It'll sound perfectly fine - but then add that G7 on the fourth line: now it'll sound like you mean it!
Let's look a bit more closely at that G7 there:
- G is the dominant note in the key of C, and the G chord is therefore also the dominant chord in the key of C.
- In the key of C, G is the 5th note to C's 1st (or tonic) note.
- In the key of C, G is the V chord to the C chord's I - and the V7 chord is the dominant 7th in that key.
G7 is the dominant 7th chord
in the key of C.
Of all the different types of 7th chords out there, dominant 7ths are by far the most commonly encountered. So commonly encountered are they that, except in expositions like this, we don't even bother specifying the 'dominant' tag - a straight '7th' is simply a dominant 7th. But if you're asking yourself '
why this chord and not that?', it's important to keep in mind that any straight 7th chord is the dominant 7th
of a particular key.
So just as G7th derives from the key of
C, C7 (
C, E, G, B♭) itself derives from the key of
F; D7 (
D, F♯, A, C) from the key of
G; F7 (
F, A, C, E♭) from the key of
B♭; etc., etc.
Introducing a C7 (from the key of F) into a song in the key of C will drive the chord progression in the direction of F. Introducing a G7 chord (from the key of C) into a song in the key of G will drive the chord progression in the direction of C, etc, etc.
Take the Kansas City example I used above, which I chorded in the key of G. In the 4th line (4th bar), we encounter a G7 chord that drives the tune onto the IV chord in G, i.e., the C. Normally, we would write the progression in the Kansas City example as follows:
I, I, I, I7
IV, IV, I, I (with the final 4 bars in the classic 12-bar blues being something like)
V7, V7 I, I
That I7 in the 4th bar indeed drives the tune in the direction of the IV chord. But the reason it does, is because it's the
V7th of the IV chord - G7 is the dominant 7th of C, the IV chord in the key of G.
To describe that G7 not as I7 but as V7/IV (read as "
the V7th of the IVth (chord)") is to identify that G7 as a '
secondary dominant', and its role in the progression is to drive the chord progression on towards its (G7's) 'secondary tonic': in this case, the C.
So... To return at last to your original question (
hurrah!), I'm suspecting that a lot of these 'odd' chords you're encountering are secondary dominants. Because it's not just the IV chord that has a secondary dominant, but every chord in the key from
ii to
vi.
So in the key of C, as gvelasco has kindly tabbed out for us, we have:
Code:
I ii iii IV V vi
C Dm Em F G Am
Each of those chords from
ii to
vi has a secondary dominant of its own (the I chord, of course, has the 'primary' dominant!). In the key of C they are:
Code:
Chord notation: ii iii IV V vi
Key of C: Dm Em F G Am
2ndary dom. 7th: A7 B7 C7 D7 E7
So, let's take a look at "All of Me" - I have the original sheet music for this, and this how my copy chords the first couple of lines:
Code:
|C | |E7 | |
|All of me_____|___, why not take |all of me__|__ |
|A7 | |Dm | |
|Can't you see_|_, I'm no good with-|out you____|___ |
|E7 | |Am | |
|Take my lips__|____, I want to |lose them__|___ |
|D7 | |G7 | |
|Take my arms__|____, I'll ne-ver |use__ |them |
|C | |Am | |
|Your good-bye…
See how the A7, 2nd line, drives you toward the Dm? How the E7, 3rd line, drives you toward the Am? How the D7, 4th line, drives you into the G7 and the G7 finally back to the C? All these 7th chords at the start of each of these lines are the 2ndary dominants of the chords at the end.
The only chord that doesn't quite 'fit' is the E7 on the first line, but of that chord you could say, idk, it's leading you into the A7 that finally brings you home to Dm .
Hope that makes sense: "detours upon detours", to use gvelasco's happy analogy; so when I write 'brings you home to Dm', what I really mean of course is 'gets you to your Dm motel for the night, on your journey back to C'!
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One final point: uke0729's mention of "
Hit The Road, Jack." The chord progression in that song is known as the
Andalusian Cadence. Normally the chord progression in a major key from the 6th scale degree down to the 3rd would go vi - V - IV - iii, (e.g., Am, G, F, Em) but in the Andalusian cadence, it goes vi – V – IV – III (Am, G, F, E). There are various 'flavours' to minor keys, but in the simplest variety, natural minor, the Andalusian cadence is written as i – VII – VI – V (as i – ♭VII – VI – V with respect to a harmonic minor key).
Once you've run across it once, you'll run across it everywhere: Beach Boys 'Good Vibrations' (verse); David Bowie 'China Girl'; Del Shannon 'Runaway'; Dire Straits 'Sultans of Swing'; Hall & Oates 'Maneater'; Nina Simone 'Don't let me be misunderstood'; Richard Hell & The Voidoids 'Blank Generation'; The Stray Cats "Stray Cat Strut" (two versions: one for the verse and another for the chorus!); The Turtles "Happy Together" (verse); Zager & Evans "In the year 2525"; The Ventures "Walk, Don't Run"; Bob Dylan "One more cup of coffee for the Road" - and of course "Hit the road, Jack" - the list goes on and on!!
ld:
