Take the 2-minute tour ×
Music: Practice & Theory Stack Exchange is a question and answer site for musicians, students, and enthusiasts. It's 100% free, no registration required.

Why does the dominant chord contain a flattened 7th while this tone is not even in the scale?
Let's take for example a C7 chord. It is a 1-3-5-b7 (C-E-G-Bb).
But the C major scale does not contain Bb. So why do we use a flattened 7th in a dominant chord? It sounds dissonant. I think it would be better if it would contain a 7th without an alteration, which produces a more pleasant sound.

share|improve this question
4  
Actually, the chord C-E-G-B is (or at least should be!) more dissonant than C-E-G-Bb! At least to my ear the interval C-B is harsher than C-Bb. To hear it more clearly, invert the intervals: B-C (a minor second) is more dissonant than Bb-C (a major second). –  nonpop Nov 3 '13 at 13:14
    
@nonpop - actually, you are incorrect here. "C7" denotes a flatted seventh in the chord, so the OP is correct. It must be specified in the chord if the 7th is to remain raised. This is notated with either a small triangle or "maj" before 7th among other things. –  jjmusicnotes Nov 3 '13 at 14:42
1  
@jjmusicnotes: I agree with everything except the "you are incorrect" part ;) Are you implying the dominant 7th chord is more dissonant than the major 7th chord? Because that's what I think the OP is claiming, and I don't agree with that. –  nonpop Nov 3 '13 at 15:04
    
It's all in the ear of the beholder.Don't forget there are 3 main '7th' chords - Cmaj7-C E G B. C(dom.) 7-C E G Bb. Cm7 -C Eb G Bb. Not forgetting the ephemeral Cm maj7 - C Eb G B.It's so important to be clear as to which you speak about. –  Tim Nov 3 '13 at 15:15
1  
@nonpop - my comment was only with respect to notation - I thought the OP was claiming that "C7" stood for a natural seventh. I agree that a major 7th chord is more dissonant than a dominant seventh generally speaking though it depends on context. Placed well, a dominant seventh chord can generate incredibly strong pull - much more than a wanton major seventh. That said, a major seventh with a delayed cadence can also create incredibly strong pull as well. Technically, the two chords are equally dissonant. –  jjmusicnotes Nov 3 '13 at 17:27

7 Answers 7

up vote 11 down vote accepted

Dominant is the fifth chord of a scale. For example in the C Major scale,the G chord is called Dominant.

The 7th of G is F natural.

So the G7 chord would be G B D F, but if you wanted to have maj7 it would be G B D F#, but the C Major scale does not include F#.

The C7 would be in the F Major scale. The key to F Major scale is Bb, and the Dominant chord would be C E G Bb. (this doesn't mean that you can't play C7 in another scale)

Edit: Now that I re-read my answer, I think I wasn't really clear. I order to find a chord,you need to ascend 3rds from the note you start(for the most common chords).

So, in the C Major scale, the G chord,which is Dominant, will be: G (ascending a major 3rd) B (ascending a minor 3rd) D (ascending a minor 3rd) F, making it G B D F. That's the reason the Dominant chord contains a minor seventh.

share|improve this answer
    
Check your first edit. Edit 2 : often, but not always, do the notes go up in thirds. It may confuse to say 'minor seventh in a dominant chord'- yes, that's the interval 'tween G and F, but a 'minor seventh' chord is something else. –  Tim Nov 4 '13 at 9:35
    
    
I didn't say it is a minor seventh chord , but it contains a minor seventh –  Shevliaskovic Nov 4 '13 at 9:56
    
I Added (for the most common chords) in my second edit. I'm not sure if minor seventh is the right word. I found it on wiki. I do these in greek,so I'm not sure –  Shevliaskovic Nov 4 '13 at 10:13
    
That's why I put "may confuse". The interval between root and 7th note in a major scale is a major 7th.When that 7th note is flattened, the interval is indeed a minor 7th. –  Tim Nov 4 '13 at 10:58

The flatted 7th is in the scale. You're just thinking about the wrong scale. The term "dominant" refers to the 5th note of a scale. In the case of C7, C is the 5th note of the F scale. The note Bb is in the F major scale.

share|improve this answer

Why does the dominant chord contain a flattened 7th while this tone is not in the scale?
Dominant has two meanings: the dominant function (that of the fifth chord in the scale), or the dominant seven chord (which may or may not have a dominant function). Practically, most musicians do not use term 'dominant' when referring to the dominant 7 chord (aka, maj min 7 chord or simply 7 chord). Most often they'll just say 'C7' instead of 'C dominant 7'. Which is what I prefer, because I reserve the use of the word 'dominant' for the chords that function as dominants.

Your're obviously not referring to the dominant chord (i.e the fifth chord) because the dominant chord of a major key is always part of the scale. You're referring to the 7 chord based off of the tonic (in your example, or some other note general) which does not function as the dominant chord of the scale (it could be, however, functioning as a secondary dominant: C7 is the dominant chord from the key of F, and it can help you modulate to F). Whenever you have maj min 7 chord that isn't the fifth chord, it may be explained by theory in several ways (secondary dominant, tritone substitution, etc... I'm not into that stuff).

In 12 bar blues, all chords can be played with an added minor 7th and it doesn't sound wrong, and the only explanation I can give for the fourth being played dominant is that it just sounds cool. The point is, if it doesn't have a simple theoretical explanation, don't look for a complicated one.

So why do we use a flattened 7th in a major dominant chord? All dominant chords have flatted 7s that are part of the scale (for example in the key of C, G7 is the dominant and it's 7th is F). You probably meant: why do whe play dom 7 chords that are not the fifths (functional dominants)? So again to summarize, it could be explained using theory (read about secondary dominants, modulation, tritone substitution...) or it can have no explanation at all. Some people like chicken with ice cream, why not? This is art, not math.

share|improve this answer

The other answers to this are all good. However, I can see how they could be confusing to many people. So here is my attempt at explaining why the 7 in a dominant chord is lowered.

First off you need the definition of the dominant 7th chord:

          ♭7
 Major 7th 5
 contains  3
           1

This means, as you already know, that building a Dominant chord off of a C, would result in C, E, G, and B♭.

Now, to understand why the 7th is flat, you need to know that the dominant 7th chord only happens naturally on the 5th of a Major scale:

enter image description here

You can easily double-check me (to make sure that I am telling the truth) by first off knowing that a dominant chord consists of a M3 (1 to 3) a m3 (3 to 5) and another m3 (5 to 7).1 Now, what is the interval between G and B? Yep, a Major 3rd (M3). And between B and D? You guessed it, a minor 3rd (m3). And finally another m3 between D and F. You can also double-check me on all the other 7th chords by checking the intervals between the four notes to see if they contain the right intervals for the given chord. I.E. Major 7th: M3, m3, M3... Yep.

So now that we have proven that a 7th chord built off of the 5th of a key is truly a naturally happening Dominant (you believed me anyways, didn't you?), we can easily see how the B in a C dominant 7th would be a ♭.

Think about it. Since the Dominant 7th chord is naturally occurring on the 5th, let's find a fifth below C. That's F, isn't it? Here are the naturally occuring 7th chords in F major:

enter image description here

Look! The fifth is a naturally occurring dominant chord containing C, E, G, and B♭! (don't forget that key signature!)

So that is why we end up with a B♭ in the C major key signature. It's because the Dominant 7th chord is really based off of the Key a P5th below.

1 http://www.socraticmethod.net/music_theory/seventhchords.htm

share|improve this answer

It sounds dissonant because it is ! It is, and has been, for hundreds of years,the means of moving to the subdominant chord. Containing a most unstable tritone, as in E and Bb, in your example in Cmaj.,it needs to resolve to an F chord. Don't worry that Bb is not in the key of C, as it's in F, where the music is going, albeit briefly. Your idea of using a major 7th is fine, but it doesn't push towards the subdominant in any way. Think along slightly different lines - the chord that pushes back to C is actually G dom.7th, which contains a tritone, AND an F note, which isn't in the Gmaj.scale.

You'll find the #5th does the same sort of job (as in C+ - C,E,G# to move to F); again G# is not in the key. Just because you're in the key of Cmaj., doesn't mean you can ONLY use the 'white notes'.

share|improve this answer
    
how do you know that it need to be resolved exactly to an F chord? Why not Bb chord for example? –  Jesus Christ Nov 9 '13 at 20:39
    
And strangely, if it's named 'dominant', it must dominate on all other chords in the selected scale, I think. So other chords must be resolved into dominant, not vice-versa. –  Jesus Christ Nov 9 '13 at 20:46
    
@Jesus - most people are of the opinion that the sound of a dominant seventh chord will resolve to the chord a 4th above it. This happens in most tunes, many times. Yes, of course, you can play any chord after any other chord, but dominant to tonic, because it sounds natural, is played so very often.The theory follows the fact, not vice versa. –  Tim Nov 11 '13 at 8:32

The "dominant seventh" is so called because it is the result of adding a 7th to a V chord of a major key (called the dominant chord) without an accidental. For example, because C is the dominant chord of F major, the notes of a C7 chord should agree with the key signature of F major. The reason the 7th is a Bb is that that note is part of the F major scale.

I personally favor using the term "dominant seventh" only in cases where it is either the dominant chord of either the key signature or is dominant relative to the following chord, a concept called "secondary dominance". For example, if the song "All through the night" is played in C major, the opening chords are:

   C      F            D7         G
   Peace, my child let God attend thee

The D7 chord is the dominant chord of G, which would be the dominant chord of C major. Because the D7 chord is going to resolve into G, it uses the nodes of the G major scale, which includes an F# but not a C#. That particular chord I would refer to as a "dominant 7th" because it is the dominant chord of the following chord to which it resolves. There are some other contexts, however, in which that same shape of chord is used but does not resolve in that fashion. In such cases, I prefer to refer to that chord shape as a "major minor seventh", meaning a major chord with a minor seventh [relative to the root] on the top.

share|improve this answer
    
That D7 is known as a secondary dominant. There is absolutely no need to put (#3). It makes no sense - I thought you meant play F## in the D7 chord, which obviously it doesn't. When a chord has just a 7 after it, as it is the most used sort of 7th, it always means dominant, so will always have a major 3rd. The main place to find unresolved dom.7ths is in Blues. –  Tim Nov 4 '13 at 7:44
    
From the standpoint of someone playing chords, you are correct that the chord names are interpreted without regard for the key signature. My intention was to make clear that secondary dominant sevenths have accidentals because their pitches are what they would be in the key of the chord they lead into. I'll tweak the way I wrote things to make it clearer. –  supercat Nov 4 '13 at 17:06
    
@Tim: In any case, my point was to mention that a major minor seventh is often called a "dominant seventh" because the dominant chord is the only major chord whose seventh will naturally be a whole step below the octave. –  supercat Nov 4 '13 at 17:14

The flat 7th is in the overtone series of the root note. For example, let's say you play an A7 dominant chord starting with the A at 440 Hz. The frequencies in the overtone series for the A are:

Frequency  Closest pitch
440 Hz     A
880 Hz     A
1320 Hz    E
1760 Hz    A
2200 Hz    C#
2640 Hz    E
3080 Hz    G
3520 Hz    A

Notice that A, C#, E, and G – the notes in the A7 chord – appear in the overtone series of A within 4 octaves. G#, the 7th in the AMaj7 chord, appears much, much later in the overtone series.

share|improve this answer
2  
As I already said in my comment though, the 7th overtone isn't particularly well-represented by the minor 7th in well-tempered tuning, so for much of western music you can't apply this argumentation really well. –  leftaroundabout Nov 3 '13 at 21:44

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.