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Is there any formula to apply extended chords just like triad chord (IM-IIm-IIIm-IVM...like this). Thanks..

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If by 'extended chords' you mean adding fourth voice to the triads then sure there is:

Imaj7 IIm7 IIIm7 IVmaj7 V7 VIm7 VIIm7(b5)

You simply stack another third on top of your triad that belongs to a given key. If you mean the actual extended chords beyond seventh then the procedure is still the same - just keep stacking diatonic notes.

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    Those are seventh chords, not extended chords. – ex nihilo Feb 15 at 13:42
  • Good point. I liberally interpreted the 'extended' it this questions 'adding fourth voice' as this is what context seem to suggest. Not 100% sure though – Jarek.D Feb 15 at 14:44
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To expand on Jared.D's answer. Diatonic chords are chords where all the notes belong to the key you are in.

The reason we use the notes we do to form the diatonic triads is because those notes all belong to the key, stacked in diatonic thirds.

For example the key of c is made up like this

C D E F G A B C

To spell a C chord in this key we start on c, skip a note then E, skip a note and then G.

That turns out to be major.

The next chord is a d chord. D, skip, F, skip, A.

That turns out to be minor. Due to the F natural and not F# (minor third interval between 1 and 3)

If you continue that pattern you get the triads you mention.

Now, for 7ths you can just skip another note and add a 7th of some flavor, determined by the diatonic note in the key you are in.

The I (one) chord would be C E G (skip a note) and then B. This a major 7th chord. Cmaj7.

D would be D F A (skip) C. ii-7 (2 minor 7).

The rest of the chords are:

Imaj7 ii-7 iii-7 IVmaj7 V7 vi-7 vii-7(b5)

Note minor chords get lower case letter. The dash denotes minor 7th. Major 7ths get a "maj". The dominant 7th just get a "7".

  • This answer discusses seventh chords, but the OP asks something about extended chords (which include 9ths, 11ths, 13ths). Still, I'm not exactly sure what the OP is asking. – ex nihilo Feb 15 at 14:01
  • @davidBowling I wasn't sure either. But since they mentioned triads and not sevenths I thought sevenths was the intent here. If they said I know how to build triads and sevenths but what's beyond that I would have gone with 9ths etc. I'll leave for now and wait for the OP to weigh in. – b3ko Feb 15 at 15:09
  • Suppose major scale formula is I- maj; ii-mi; iii-mi; IV- maj; V7; vi-mi; VII-dim. Like this, is there any formula to use 9th / 11th / 13th series chords? Jarek.D and B3ko has rightly given the formula of 7th series chords as Imaj7 ii-7 iii-7 IVmaj7 V7 vi-7 vii-7(b5). I tried in this way before but I felt that it doesn't match the notes of the song like triad chords. Suppose if I use C maj7 instead of C maj triad on a C major scale it doesn't sounds good or matching like C-maj triad. I try to use the extended chords in my own logic. That’s why I wanted to know that if there is any formula. – Sonjoy bhattacharya Feb 16 at 10:57
  • Not every song will sound good if you use 7th chords in place of triads. There are more factors involved than just "its diatonic to the key". This is even more true with chords like 9ths, 11ths, etc. You can just keep stacking notes up in thirds but there will clashes depending on what chord, the melody note, and what notes of the chord are being played, the voicing. If you don't think the 7ths sound good when substituting for a triad, it's going to be even harder with extended chords. In Rock/pop and other styles its fine to just use triads. – b3ko Feb 16 at 13:57

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