I noticed there's a preference towards the odd numbers when forming chords:

1 3 5 7 9 11 13

And chords are usually built with 1-3-5, 1-3-5-7, 1-3-5-7-9 and so on. And they like to talk about 7th chords, 9th chords.

So it seems like odd numbers are emphasized. Why aren't the even numbers? Like 2 4 6 8 10 12 14

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    Did you mean to include '1' in your list of notes that you've observed a preference towards? The first note of the chord is '1' because it's the first note in your chord... and every chord has to have a first note. – topo morto Oct 28 '18 at 9:09
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    Following on from that, there's an obvious tendency towards 3 5 7 11 13 because of Western music's orientation around triadic harmony - those are the degrees that you get when you stack thirds. At its core, this question seems to be "why do we have triadic harmony"? – topo morto Oct 28 '18 at 9:18
  • @topomorto if you go 2,4,6,8,etc you stack thirds as well. – foreyez Oct 28 '18 at 15:47
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    If you go '2, 4, 6', then your 'first' note is 2 - but Because it's your first note, you should call it '1'. If you then maintain a gap of 2 between each subsequent note in the pattern, then your chord is just 1, 3, 5... – topo morto Oct 28 '18 at 15:56
  • music.stackexchange.com/questions/8037/… may be relevant. – topo morto Oct 28 '18 at 16:50

The 6th is in common use! But the blend of notes just happens to sound far more consonant using the 3 and 5 over 1 as a start point. When we get to above 6, then it's pretty apparent that no new notes are forthcoming. 8 is octave, 10 is 3 again, 12 is 5 again. Why could those be part of it, when they're not bringing anything to the party?

2 and 4 also get included as good ones to invite, as they appear as 9 and 11, farther away from the 3 so they won't sound too dissonant. And sometimes in their own right as 2 or 4 replacing that 3, and getting called 'suspended'.

  • right the 6th is the only one really given its own chord. If 2 or 4 replace an odd one it's called suspended. so the even notes are being treated second class. I know with 9, 11, 13 eventually get to the even notes in the scale, but that's only in the second octave. This question stemmed from learning about extended chords like 9ths, 11ths, etc. and practicing arpeggios so I was wondering why not practice even ones then. – foreyez Oct 28 '18 at 15:50

Since "1" is the tonic of any scale by definition, and 1 3 5 the tonic triad (say, C E G in C major), then it's not really surprising that these odd numbers (merely by convention) come up more often than any others.


The basic chords are triads. You can explain this from the harmonic series. Starting on C we have C, C (octave above), G, C, E, G, Bb (sort of), C, then it goes scalic. See why the basic 'C chord' is C, E, G rather than C, D, F?

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    Could you expand on this, so more readers may comprehend, please? – Tim Oct 28 '18 at 14:01

The diatonic scale (pop music, seven notes, major, minor, dim, etc.) builds chords using alternate notes. If there's an even number then you can't move up to a next key because alternating notes lands you back on the note starting the scale instead of the next note up the scale.

C-E-G-B ... then D, not C.


The standard theory term for what you ask about is tertian harmony. Which is harmony based on chords of stacked thirds.


The usual answer to "why" is often answered by pointing out the connection between a major triad and the harmonic/overtone series. TL;DR The strongest tones in the series are those which create a major triad, therefore people are predisposed to prefer that sound.


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