This cheery little jig is in D ionian, and can consequently be accompanied with the following chords: D major, E minor, F# minor, G major, A major, B minor and C#diminished.
In the simplest version of the chords I have only used chords I and V for the A part, following the first two rules of folk music accompaniment, that chord I always goes at the beginning and that chord V goes on every seventh foot tap, resolving to chord I at the end of each A and B part.
The B part has a clear chord IV section in bar 3, with a long G note at the start of the bar and an E on the second dominant beat (fourth quaver / eighth note). For symmetricity I have changed to chord IV in the seventh bar too. Although this is not really necessary it works because you can always substitute chord IV for chord I at any time.
In this version I have played D/F#, the first inversion of the D chord instead of the second bar of D. This works well because although it still contains the notes of a D chord, the D/F# chord has the F# at the lowest pitch within it, which sets up a nice little bassline to lead up to the G chord which follows it. In bar 4, rather than just playing a whole bar of A, I have resolved to A from the chord which is a fifth above it within the key, aka E minor. You can resolve down a fifth to any chord which you feel is played for too long- Em to A is down a fifth (E, D, C, B, A). This would work just as well in any context, you just have to use the right kind of chord for the desired root note within the key. For example if you were playing in D major and there was a long section of chord IV, you could replace the first part of that section with chord VII, which is a fifth above it. In the case of D major this would be D resolving to G. To resolve to chord VI you would use chord III, which is a fifth above it. In the key of D that would give you F#m resolving to Bm, etc etc.
In order to get from my G chord in bar 3 to the E minor in bar 4, I have used D/F# as a convenient link to set up a nice bassline between the two (G – F# – E). In this instance D/F# is acting as a substitute for F#m. This is a very common folk trick, to use the first inversion of chord I as a less miserable sounding substitute for chord III.
For the rest of the section I have used D/F# to provide a sense of movement between my other chords. Varying the “rate of harmonic change” on the second or third run through a tune can really add a lot of energy, as is the case if you compare this version of the B part to the simple version which changes more slowly.
In the B part I have switched chord I (D) to its related minor, chord VI (B minor). I have followed this up with another substitute for chord I, F#m. Any major chord has two possible substitutes; its related minor, whose root is two notes below it in the tune’s scale (D – Bm) and also the minor whose root note is two notes above it in the tune’s scale (D – F#m). As I started the section on a minor I have carried on the “tale of woe” chord progression with the other available minor substitution for chord I. I have then continued on to the G chord as normal, before I hit my seventh foot tap and go back to chord V.
In this version of the tune I have contrasted the rate of harmonic change every two bars, in order to make the accompaniment sound like a conversation between two speakers- one with a slow, assured way of speaking and the other with terrible verbal diarrhoea. The chord “Dmaj7/C#” is a substitute for C# diminished which is easier to play and sounds less dissonant. It contains the notes of a D major 7 chord (D, F#, A, C#) but with the C# at the lowest pitch in the chord in order to provide a nice bassline link from D down to Bm (D – C# – B). It is a valid substitute for D major because in a major key chords I and IV can always be replaced with major 7 tetrads, no matter what inversion those tetrads are in.
I have replaced all the minor chords in the tune with minor 7s to make them sound jazzier. You can always do this, in any key. The A chord has become A dominant 7 (to give it its full title- it would more commonly be known as A7 for short). This is because chord V in a major key has to be a dominant 7 tetrad rather than a major 7.
In the B part I have sped up the rate of harmonic change in order to add energy. The frequent use of D/F# as a passing chord provides movement in the bass and makes a nice hum-able bass line. Notice that I have contrasted four bars of normal major chords against four bars of related minor substitutions. Again, this give the accompaniment a conversational feeling. If you begin with B minor instead of D, I prefer to keep the following chords minor too, eg F# minor instead of the happier D/F# or E minor instead of G. This is purely my own personal preference, but to start a section with a dark related minor substitution and then revert to the standard majors feels to me as if the harmony began to tell a story about something that went horribly wrong, but then got bored half way through and changed the subject.