More on the meaning and usage of "dominant 7th"

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More on the meaning and usage of "dominant 7th"

Postby Bob Lewis » Thu Jun 04, 2009 1:29 pm

The following is an epilogue to a previous bit on 7th chords. See Different types of 7th chords

The term "dominant" originally referred to relative physical position, not some romantic notion of how something feels or sounds. While additional meaning may have been attributed to a term, it's interesting or enlightening to look at its origin and realize both the evolution of usage and the corruption and then ambiguity of the meaning. In terms of the use of "dominant 7th", the ambiguity in common usage and even published academic presentation is stunning, even obtuse.

---UP---
Dominant
Mediant
Supertonic
Tonic
Leading tone
Submediant
Subdominant
--DOWN--

-Dominant is a fifth above the Tonic. The name means "above"
-Mediant, as the word implies, is halfway between the Tonic and the Dominant
-Supertonic, as the name implies, is just above the Tonic
-Tonic, the root tone
-Leading tone, demands resolution to the Tonic. In context, it suggests upward motion, so lies immediately below the Tonic.
-Submediant, as the word implies, halfway between the Tonic and the Subdominant
-Subdominant is a fifth below (or sub-) the Tonic

An example with the C scale would look like the following:

G
E
D
C
B
A
F

The fifth interval, or more precisely the perfect fifth, is significant throughout music theory and the physics of music.

The above is the natural order of scale degrees. The familiar sequence is with inversions to place all of the tones in the same octave, the Tonic then at the root of the sequence, as follows:

---UP---
Leading tone
Submediant
Dominant
Subdominant
Mediant
Supertonic
Tonic
--DOWN--

This is the same as the diatonic scale or indeed is the diatonic scale:

---UP---
7 - ti - Leading tone
6 - la - Submediant
5 - sol - Dominant
4 - fa - Subdominant
3 - mi - Mediant
2 - re - Supertonic
1 - do - Tonic
--DOWN--

An example with the C scale would look like the following, a C diatonic scale:

B
A
G
F
E
D
C

Because of the inversions, the subdominant started as a fifth below the Tonic but ends as a fourth above the Tonic. An octave is a fifth plus a fourth, so inversions change the interval relationships. F to C is not the same interval as C to F, when both move in the same direction, say F->C->F. Once in this practical sequence with the Tonic as the first tone, the "root", the meaning of the names of the scale degrees are not as readily apparent, or intuitive interpretation could be mistaken.

Reference: Music Theory, George Thaddeus Jones, Barnes and Noble, 1974.

My rant on musical urban legends:

Harking back to previous discussion, it is well documented that Major-minor 7th chords, what we call just "7ths" on the autoharp, are commonly known as "dominant 7ths" as a class of chord structure. While that may be common currency, it is still based on a corruption of the term "dominant" and injects ambiguity as to exactly which Major-minor 7th chord is being referenced. As a generic term, "dominant" adds no value until wanting a letter designation to add to the number 7 (D7),not to be confused with (d7), as in diminished. A bare "7" says as much, since it is the most common and is easily considered the default type, and since the alternative M7 or m7 or °7 or Ø (half diminished) are clearly distinctive. It may in fact be a short form for "dominant-like 7th" or "sounds like a dominant 7th", which would be entirely accurate in formal terms, synonymous with Major-minor 7th as a generic structure.

Using a scale degree name in reference to any chord is supposed to indicate that the chord is built with that scale degree as the root. With common usage of the term "dominant 7th" that would not always be the case, so it seems like practitioners could have and probably should have picked a different word than [dominant] as a class name or agreed that "7th" alone was usually sufficient.

Personally, I am attracted to the alternative "Major tritone" which reflects the generic structure of the chord (M+m+m) in similar fashion to the formalized "Major-minor 7th". I believe T7 would be a useful short form. Note that a "minor tritone" would be equivalent to the diminished 7th, and a "tritone Major" would be equivalent to the half diminished, so there need be only one distinctive, unmistakable usage of the term [tritone], and then only when simply "7th" would not suffice.

Note that there are not really such intervals as a minor 7th or a Major 7th. The 7th chord names derive from the third interval that is added to the base triad to form the 7th chord. The 7th tone is considered either natural or flatted, no major or minor. Those terms rightfully refer exclusively to the two types of third intervals, Major and minor. Yes, one 7th tone may be a half step higher or lower than another, but there is no "natural", "Major" or "minor" involved. The 7th scale degree cannot be "sharped", because it would then equal the tonic octave a half step above it. There is only a natural 7th tone and a "flatted" 7th tone, no major and minor 7th intervals. Raising of a 7th tone could only occur in a modal scale other than a Major or Ionian scale.

The minor scale indeed raises the fifth in that key signature in order to achieve the leading tone. Em Aeolian with a key signature of G relies on a D# to achieve a B7 chord for the harmonic minor scale. That raises the 7 tone D of the E minor scale to D#. E harmonic minor would be our familiar Em-Am-B7 progression, playable only if tuned to support at least (4) related keys. The key of G would have to be accompanied by D, A, and E in order to get to that B7. Thus, when referring to the III7 of a key, that B7 out of G for example, one could as well be referring to the V7 of the relative harmonic minor (Em), played in that same key signature when minimizing accidentals rather than orienting to the E root, another odd, compulsive practice, perhaps born of practical (performance) considerations. I mean to say that the key signature for Em should look like G with one sharp, not E with four sharps.

Before becoming a complete ramble, I will stop here.

Bob Lewis ♫
boblewis@autoharpworks.com
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