Harmonised Major Triads
All triadic chords ( known as triads) in major scale harmony are derived from the major scale.
There are 7 notes in a scale which produce 7 triads.
Let's take a C major scale as it has no sharps or flats.
C D E F G A B C
Triads in the C Major Scale
To get the first triad we take three alternate notes of the scale. In other words, we are stacking up 3rd intervals.
I C E G Gives us a Cmajor triad. The interval from C to E is a "major" third. The interval from C to G is a perfect fifth.
II D F A. Gives us D minor triad. Minor 3rd and a perfect 5th
III. E G B. E minor triad. Minor 3rd and a perfect 5th.
IV F A C. F major Triad. Major 3rd and a perfect 5th.
V G B D. G major triad. Major 3rd and a perfect 5th
VI A C E. A minor triad. Minor 3rd and a perfect 5th
VII B D F. B diminished triad. Minor 3rd and a diminished 5th
These are called diatonic triads as they are all built from the major scale.
The order of diatonic triads should be memorised.
Common chord progressions are made up of different combinations of these triads.
C Major Root Position
These triads shown above are in "root position" meaning that the order of notes in each triad is root, 3rd, 5th.
Then we jumble the notes of the triad around!
C Major 1st Inversion
First inversion means we have the order of notes 3rd, 5th, root.
C Major 2nd Inversion
The last inversion is the 2nd inversion which has the order of notes 5th, root, 3rd
Standard chord voicings
There is one instance of each note in a triad. Common chord voicings can have multiple instances of notes in various orders. This bulks out the triad to give a fuller sound!
For example a standard C major chord will have the notes C, E, G, C, E. That's root, 3rd, 5th, root, 3rd.
If we analyse this chord...
Strings 5,4,3 form a C major triad in root position. (C,EG - root, 3rd, 5th)
Strings 4,3,2 form a C major triad in first inversion. (E,G,C - 3rd, 5th, root)
Strings 3,2,1 form the triad in second inversion. (G,C,E - 5th, root, 3rd)
A D minor chord will have D, A, D, F. That's root, 5th, root, minor 3rd.
You can actually see that the top three strings form a D minor triad in 2nd inversion! (A, D, F - 5th, root, minor 3rd)
A big G major chord has the notes G, B, D, G, B, G. That's root, 3rd, 5th, root, 3rd, root.
If we analyse this chord....
The bottom three strings are a G major triad in root position. (G,B,D - root, 3rd, 5th)
Strings 5,4,3 form G major in first inversion. (B,D,G - 3rd, 5th, root)
Strings 4,3,2 form G major in second inversion. (D,G,B - 5th, root, 3rd).