Music Theory Made Simple #44: Diatonic 7th Chords

stevel

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Now that we've discussed Diatonic Triads, and 7th Chords in general, dealing with Diatonic 7th Chords is nothing new other than learning the qualities of the chords on each scale degree.

Maybe the only thing here not so obvious is the symbology. Like with Triads, there are varying traditions, inconsistencies, variants, etc. IMHO it's best to just understand that these distinctions exist and be familiar enough with them so you can figure out from the context what's going on.

Upper Case Roman Numeral with an Upper Case "M" and 7 is a "MM7", thus Major 7th Chord.

Example:

IM7 = Tonic Major 7th Chord.

Upper Case Roman Numeral with just 7 is a "Mm7" or Dominant 7th Chord.

Example:

V7 = Dominant 7th Chord.

Very Important Side Note Here!:
Even though the Mm7 appears naturally (Diatonically) on the Dominant Scale Degree, we call ANY 7th chord with the Mm7 structure a "Dominant 7th Chord" because it is possible to encounter them non-Diatonically.

Lower Case Roman Numeral wand 7 is "mm7" or a Minor 7th Chord.

Example:

ii7 = Supertonic Minor 7th Chord

Lower Case Roman Numeral with the suerscript "slashed degree symbol" (ø) and 7 is a "om7" or Half Diminished 7th Chord.

Example:

viiø7 = Leading Tone Half Diminished 7th Chord

And as follows logically, a Lower Case Roman Numeral with a diminished symbol and 7 "o7" is a Fully Diminished 7th Chord.

Example:

viio7 = Leading Tone Fully Diminished 7th Chord

Again, there are varying schools here. What I've given you above is the "academic" version widely used in universities (in the States) with a traditional Common Practice Period focus on Harmony/Theory. In more Jazz-based programs we tend to see a Roman Numeral symbology that more closely reflects the way Letter-based naming works:

IMaj7 (also, the "M" or "Maj" may be replaced by a "delta" triangle (∆*)

*I'm avoiding using too many of these symbols because while I can generate them with my "alt" key, they may not appear consistently in various internet fonts

V7 (nothing different here)

IIm7 (or IImin7, IImi7, II-7, and even iim7, etc.)

IIm7b5 (or IImin7(b5), II-7b5, etc.)

VIIo7 (or VIIdim7, etc.)

Another important side note: In Jazz and Pop music, and even in academic circles when the context is clear 7th chords are being discussed, very often people will just say "diminished" when they mean "fully diminished 7th". If they "C diminished" they probably mean Co7, and not just the Co Triad (they might, but it's less common they mean the Triad, and context should help you determine what they mean). With chord symbols, they usually do put the "7", but sometimes you will simply see "Co" and they mean Co7. I've even seen the "half diminished" symbol by itself after a chord! That makes a little more sense since there's no such thing as a half diminished triad, but IMHO it's always better to include the "7" on 7th chords.

Less of a side note, but still important:
I'm going to use "m7b5" for half diminished because of the more commonplace nature of that symbol, plus it's easier to deal with in text. So just know right here and right now, m7b5 IS a half diminished 7th chord.

OK, back to the program.

Diatonic 7th Chords in a Major Key:

IM7 ii7 iii7 IVM7 V7 vi7 viim7b5

So the qualities are:

M7 m7 m7 M7 Dom7 m7 m7b5

Notice this is not too different from the Triad qualities - remember?

M m m M M m o

Everything that was a MINOR TRIAD is a MINOR 7th when you add a Diatonic 7th to the chord.

Everything EXCEPT V that was a MAJOR TRIAD (I and IV) becomes a MAJOR 7th when you add a Diatonic 7th.

V - is different - it was a Major Triad but becomes a Dominant 7th (structure) with the addition of the Diatonic 7th.

viim7b5 is somewhat different as well - it was a DIMINISHED TRIAD but now it's a HALF diminished 7th chord with the addition of a Diatonic 7th.

Remember how I kept telling you over and over to learn your Triad qualities? I'm going to tell you once here. LEARN THEM FOR 7ths TOO!

Major:

IM7 ii7 iii7 IVM7 V7 vi7 viim7b5

M7 m7 m7 M7 7 m7 m7b5

or if you like

IMaj7 IIm7 IIIm7 IVMaj7 V7 VIm7 VIIm7b5

Now for Minor. I'm going to start with NATURAL Minor as I did with Triads. You should remember that since Major and Minor Keys are related (there's one of each that share the same Key Signature) that the Qualities of Major starting on "6" will be the same order (you remember all this don't you?):

m7 m7b5 M7 m7 m7 M7 Dom7

i7 iim7b5 IIIM7 iv7 v7 VIM7 VII7

In, oh, let's do E Minor, this would be:

Em7 F#m7b5 GMaj7 Am7 Bm7 CMaj7 D7

WAIT. WAIT. WAIT. Hold your darn horses. What's going on? There's a Dominant 7th on the VII...that' can't be right?????

It is. Remember, the "Dominant" word refers to the STRUCTURE of the 7th chord (Mm7) and that's what the structure of a chord using the Diatonic notes of a Natural Minor Key turns out to be built on scale degree 7 (the Subtonic).

Did you also catch that the "v" up there is Lower Case?

This is the same problem we had with Triads. In Minor Keys, Diatonically, 5 is "v" (minor v) and 7 is VII (bVII).

You remember the problem we ran into? This is a great illustration. VII to III in a Minor Key is the same as V to I in the Parallel Major. Now, I haven't said much about this but the V to I progression is THE defining characteristic of Tonal Music, including many styles descended from it (which we still play today). "II-V-I" in Jazz - see the "V-I" there?

OK, I just lied. Actually, the MOST defining progression of chords in Tonal music is V7 to I. That's FIVE-SEVEN to ONE. The Dominant 7th chord to the Tonic.

So here's our even bigger problem when we add 7ths to our chords: VII7-III in Minor Keys sounds just like the most defining progression of Tonal music, but leading to the wrong Tonic!

(Another side note here: in Tonal music, not all chords are 7th chords - they were more freely intermixed than in a lot of modern styles where primarily Triads (or power chords!) or primarily 7ths (and 9ths etc.) are used)

However, they applied the same process in Minor Keys with 7th chords that they did with Triads - on Dominant FUNCTION chords (V and VII) they altered the Subtonic scale degree (7) by raising it a Semitone and turning it into the Leading Tone, which is represented by what we call the Harmonic Minor Scale.

This means "v7" and "VII7" become "V7" and "viio7" respectively.

So in Minor, we really more commonly encounter (in the CPP mind you):

i7 iim7b5 IIIM7 iv7 V7 VIM7 viio7

Yet another side note: Remember how I said III as a Minor Triad DIDN'T use the altered Subtonic because it was a chord that didn't have a Dominant FUNCTION (this is different from Dominant STRUCTURE, OK?). BUT, we could (because people have) use it to make a III+ chord?

Well, the same thing happened with chords that contain the 7th scale degree in Minor - the Dominant FUNCTION chords (V and VII) ONLY got the alteration in CPP music.

But in later styles, people started adjusting that note in any chord it was a part of, which in this case is I7 and III7.

It turns i7 into a imM7 (minor-Major 7th) and IIIM7 into a IIIM7#5. That introduces those two additional forms (not the 5 traditional types, and not the altered Dominant type) of 7th chords.

Again, like with Triads, the V7 and viio7 were SO commonly used, these were considered to be the "default" state and thus Diatonic.

In CPP music, imM7 (or any mM7) and IIIM7#5 (or any M7#5) simply did not exist.

Did the "v7" and "VII7" get used? Yes, but rarely. Really rarely. You'd have to pore over tens of thousands of pieces to find more than a handful of examples of each (you'd find millions of I and V7 chords by comparison).

Actually, here's an interesting thing: Major 7th chords are actually fairly uncommon in CPP music (comparatively speaking). Far and way, Dominant 7th (both the structure and the functional V7) forms are the most common, and most important. After that, probably the Fully Diminished 7th is most common (and important). m7 chords are seen with regularity, and m7b5 chords are not uncommon - though their uses are more specific which maybe relegates them to a tie-breaker position. Major 7th chords are much much rarer. That doesn't mean you won't find them, but it means for each one you do find, you'll find tens to hundreds of the others.

This is kind of echoed in modern pop (rock) music that's not obviously Jazz influenced. You'll find plenty of Dom7 (structure especially because of Blues!) and even m7 chords. M7 lags far behind (except in the "Something" and "Kiss Me" type chord progressions where it acts as a passing idea between I and I7 a la "String of Pearls"). Fully and Half diminished chords are a special case - in many respects they're avoided for sounding "too classical" or "too jazzy" so probably far less common than in CPP music (and less important in that regard).

YOu can kind of see this reflected in the symbols used in Academia:

V7 for Dom7
ii7 for min7 = notice nothing but RN and 7. These were so common they didn't need an "m" or "M".

Same for Fully and Half Diminished - just the "o"-type symbol and the 7.

But Major 7? It got the "M":

IM7

Odd man out.

So, to Recap:

Major:

IM7 ii7 iii7 IVM7 V7 vi7 viim7b5

M7 m7 m7 M7 7 m7 m7b5

or if you like

IMaj7 IIm7 IIIm7 IVMaj7 V7 VIm7 VIIm7b5

CM7 Dm7 Em7 FM7 G7 Am7 Bm7b5

Minor:

i7 iim7b5 IIIM7 iv7 V7 VIM7 viio7

m7 m7b5 M7 m7 7 M7 o7

Cm7 Dm7b5 EbM7 Fm7 G7 AbM7 Bo7

Natural Minor uses "v7" (a m7) and VII7 (a Mm7 built on the Subtonic not the Leading Tone) in place of the V7 and vii7 (so Gm7 and Bb7 in the example above).

Furthermore, assuming Harmonic Minor could be used as a resource for building all chords, not just those of Dominant Function, "imM7" could appear instead of i7 and "IIIM7#5" could appear instead of IIIM7 (so CmM7 and EbM7#5 respectively above).

Must...resist...temptation...darn, I succumbed. I will tell you again.

LEARN THEM. You need to know the qualities for Triads and 7th chords in both Major and Minor Keys, which the variable ones in Minor. You not only need to know them, but you need to PLAY them, and LISTEN to them - HEAR how they sound (especially the different ones in Minor). It is MUSIC after all - you need to hear it as well as think about it!!!

Steve

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