Similarly for III, IV, V, VI and VII. The VIII chord means that the root note of the chord is back to the original. So it is the I chord again, and it is written as I and not VIII. When we get a major or an augmented chord in such a process, the chord is written out in capital letters (e.g. I, IV, V) and when it is a minor or a diminished chord, it is written in small letters (e.g. ii, vi). Augmented chords are written with a "+" sign, diminished are written with a "o" sign above the number.
Let us take the example of C major: CDEFGABC
The basic triads obtained by taking the first three notes from each scale degree are:
CEG – C major (I) DFA – D minor (ii) EGB – E minor (iii) FAC – F major (IV) GBD – G major (V) ACE – A minor (vi) BDF – B diminished (viio)
Again, the G major scale is: G A B C D E F# G, and the chords are:
I = G major, ii = A minor, iii = B minor, IV = C major, V = D major, vi = E minor and viio = F# diminished.
Again, F major scale is: F G A Bb C D E F, and the chords are:
I= F major, ii= G minor, iii = A minor, IV = Bb major, V = C major, vi = D minor, viio = E diminished
Thus we find that any major scale gives three major triads that together can harmonize (sound good with), every note of that scale. They are the I, IV and V chords. It also provides three relative minor chords, one related to each of the three major chords, viz. the ii, iii and vi chords. Apart from these there is a diminished chord at viio. Thus the basic chords of a major scale are:
I – ii – iii – IV – V – vi - viio
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