7th Chord Question - Roots and thirds

Question

In a 7th chord, particularly minor 7th or major 7th chords, can the actual root AND the third function as the root/tonic note?

For example, a Cmin7, C and Eb can both function as root/tonic?

I ask because I notice that melodies sound resolved when starting and ending on the third (Eb). And still sound somewhat resolved, (with an urge to carry on) when ending on the root (C).

I try to make sense of it by discerning the fact the 7th chord basically has two separate root and perfect fifths (C and G , Eb and Bb) and the latter makes up a major chord. (Eb, G, Bb) Which may present the option of choosing C or Eb as a root/tonic.

Then I ask, well which "chord" in the 7th chord is the "strongest"? As you can see, my analytical probing is never ending.

Answer 1

As I see it, there are a couple different things going on in this question, which I'll deal with in turn. The first two are unrelated to seventh chords.

• There's a confusion about the meaning of tonic.
• There's a question about the similarities of relative major and minor scales.
• There's a question about seventh chords being viewed as two chords combined.

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(1)

First and foremost, you seem to be mixing the concepts of chord, and key. Specifically, the word "tonic" always relates to the key you are in, regardless of what chord you are playing. It is the tonic that describes where the melody wants to rest, or resolve to. On the other hand, terms like "root" and "third" could be used to relate to either scales, or keys, and the context should make it clear which is which. In other words, there are two possible reference points for counting intervals, and you seem to be confusing them.

This actually has nothing to do with seventh chords. For example, your Cm chord could occur in lots of different keys. Here's a few:

In the key of C minor:

• The tonic is C.
• The root of the Cm chord (C) is also the same as the root of the key (tonic).
• The third of the Cm chord (E♭) is also the the third of the key.

In the key of E♭ major:

• The tonic is E♭.
• The root of the Cm chord (C) is the sixth of the key.
• The third of the Cm chord (E♭) is the root of the key (tonic).
  • Note that this partly explains why E♭ can sound like a good tonic

In the key of A♭ major:

• The tonic is A♭.
• The root of the Cm chord (C) is the third of the key.
• The third of the Cm chord (E♭) is the fifth of the key.

In the key of B♭ major:

• The tonic is B♭.
• The root of the Cm chord (C) is the second of the key.
• The third of the Cm chord (E♭) is the fourth of the key.

So as for which note is the "tonic" (i.e. the note that melodies should resolve to)? It really depends on what key you're playing in.

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(2)

Why do C and E♭ both sound convincing as tonics when playing this scale? You'll notice that the E♭ major and C minor (natural minor) scales share the same key signature of 3 flats. This also means they share all the same notes of the scale, but with different scale degrees (for example, the notes F-G-A♭ could be viewed as scale degrees 2, 3, 4 in E♭ major, or as scale degrees 4, 5, 6 in C minor). These keys are thus considered related to each other. You would say that C minor is the relative minor of E♭ major, or swap it around and say that E♭ major is the relative major of C minor. These same terms can be applied to chords in addition to keys. Every major scale or chord has a relative minor scale or chord that starts a minor third below it (and vice versa). Once again, this is unrelated to seventh chords.

See: Are the formulae for Minor scale and Major scales related?

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(3)

Finally, you have a very interesting question that does concern seventh chords -- can seventh chords be viewed as two superimposed chords?. For example, can a chord comprised of 1-3-5-7 be viewed as a combination of the chords 1-3-5 and 3-5-7?

I would argue that the answer is yes, to a limited degree. It doesn't affect what the tonic is, since that's determined by your key. Nor does it change what the root of your chord is. But the chord's "quality" is definitely affected by the quality of the upper chord. Let's look at some examples. For each seventh chord below, try playing the two triads separately a couple times, listening to their differences, then play them together as a seventh chord, and here how they both contribute to the resulting sound.

• Dominant Seventh = Major + Diminished

  • e.g. (G, B, D) + (B, D, F)
  • This chord combines the boldness of a major chord, with the instability inherent in the diminished chord, resulting a chord that demands resolution -- so much so that it practically defines the whole concept of western tonal music.

• Major Seventh = Major + Minor

  • e.g. (C, E, G) + (E, G, B)
  • The outgoing happiness of the major chord is somewhat tempered by the sorrow in the minor chord, leading to a sound that could be described as bittersweet, melancholy, or even a nostalgic.

• Minor Seventh = Minor + Major

  • e.g. (C, E♭, G) + (E♭, G, B♭)
  • This intense sorrow possible in a minor chord is significantly reduced and stabilized by the major chord leading to a rather laid-back, mellow or chilled-out sound. The theme from Beethoven's 5th symphony sounds dramatic over a minor chord; over a minor seventh... meh, not so much.

In each of these cases, you can think of the upper "chord" as somehow flavoring the perception of the lower chord.

Update: As @Ceart mentions, the more general term for the superposition of two different chords is a polychord. Because seventh chords are so ubiquitous, I don't think they are usually thought of as polychords, although technically they could be. When seen from that standpoint, here is a related question: Difference between Polychords and Extended chords

Answer 2

There are mainly two ambiguous seventh chords (or four, depending on your definition). Let's choose A and C as the respective root notes:

Am7 = C6 Am7(b5) = Cm6

where = means 'has the same notes as'. There is no way to distinguish between those chords if you don't require the root to be the lowest note. Of course, the context can provide some hint as to which chord is meant, but the question which chord it is is mainly a theoretical one, because it does not affect the way you play it, neither does it affect the way you play over it (when playing a melody).

In some cases an A major 7 chord can be seen (or, actually, heard) as a C#m chord with an added b6. This is definitely rare because the b6 is normally no 'allowed' tension on a minor triad, but it can occur with line clichés, where a melody is moving chromatically over a static chord (e.g., 'James Bond theme').

However, in most practical cases there is no ambiguity in seventh chords, especially not if you take the musical context into account.

Answer 3

If I understand your question clearly, the Cm7, with C Eb G and Bb is actually an inversion of Eb6, with Eb G Bb and C. So to an extent, when either is played, it could become a rest point, although Eb6 is probably a more final sounding chord. If the piece is in Cmin., then the Cm7 could be a final chord. The more defining factor is usually the note played lowest. If C, the chord is likely to be Cm7, if Eb, then it'll be Eb6.

In answer, no, there can't be two roots in a chord, but there is an ambiguity between these two, which is slightly confusing you.

Answer 4

It sounds like you are thinking of it as a polychord. The "strongest" chord in your seventh chord will depend on the melodic context. It could be useful for modulation, i.e. changing the tonic.

For example, you could use the progression:

Dm7-G7-Cmaj7-Am7-C/G-D/F#-G

or

ii(of C Major)-V-I-vi-I/IV(of G Major)-V-I

To modulate from C Major to G Major

Answer 5

In a 7th chord, there is one root, one third, one fifth and one seventh. The fact that you will four notes forming intervals of 5ths in the chord doesn't matter.

can the actual root AND the third function as the root/tonic note?

Only the root can act as the root/tonic note. In Cm7 (C,Eb,G,Bb), the root is C. If you take Eb as a root, it will be a different chord - the Eb chord.

I'm not sure that this is what you are looking for, but if Eb of the Cm7 chord is on the bass, the chord will be on first inversion. The C would still be the root note, but Eb would be the lowest one.

A melody can end on any note of the chord (1,3,5,7). It is really common to start and end on the 3rd, but the 'resolved' part would be the same for the 1st as well.

Answer 6

Roots and Tonic notes are usually not the same thing. The roots are the notes on which chords are built. Tonics are simply the technical name for the first note of the scale.

There is off course chords build on the tonic note of the scale ( The tonic chord.) where the tonic is the root note of the chord but for all the other chords this is not the case.

For example, a Cmin7, C and Eb can both function as root/tonic

Either one can be the tonic note (Depending on the scale.) but it is clear that this chord is build on the C note. Hence the name thus it clearly does not have the Eb for the root.