Diatonic chords in any major key can be labelled as I – ii – iii ... Step 10: Here’s a version that uses seventh chords and different inversions. Once you start to use borrowed chords ...

Haydn’s Symphony No. 101 in D major, ‘The Clock’, is in a major key and uses mainly diatonic chords: A dominant seventh is used at the end of the phrase before the first time bar.