Welcome to the fascinating world of guitar chords and harmony! While this third report is not meant to replace any of the fine harmony / theory books available that elaborate in greater detail, I think you will find it contains even more information that you can quickly and easily use to enhance and expand your own guitar playing regardless of what style of music you play. So let's get right into it!For any chord type, you can always substitute another chord based on the b5th degree (Gb) of the major scale. So, when you see a C7th, C major 7th or C minor 7th chord, you could substitute a Gb7th, Gb major 7th or Gb minor 7th instead.Diminished 7th chords can often be used to connect 2 other chords to each other. Let's say your chord progression was C major 7th--> D minor 7th--> E minor 7th--> F major 7th. You could now play C major 7th--> C#Dim 7th--> D minor 7th--> D# Dim 7th--> E minor 7th--> F major 7th instead.Minor 7th#5 chords can also be used to connect 2 other chords to each other as well. Let's say your chord progression was C major 7th--> D min 7th--> E min. 7th--> F major 7th. You could now play C major 7th--> C# min. 7th#5--> D min. 7th--> D# min. 7th#5--> F major 7th instead."Backcycling" is another way to find substitute chords. Let's say your chord progression was C major--> G7th--> C major. Find the note that's a perfect 5th above G and add a chord based on that note which would be a D note. Now your chord progression could be C major--> D minor 7th--> G 7th--> C major. Next, let's find the note that's a perfect 5th above D and add a chord based on that note which would be an A note. Now your chord progression could be C major--> A7th--> D minor 7th--> G7th--> C major. Next, let's find the note that's a perfect 5th above A and add a chord based on that note which would be an E note. Now your chord progression could be C major--> E minor 7th--> A7th--> D minor 7th--> G7th--> C major.Hopefully, this third report has helped even more to clarify some of the confusion and mystery that surrounds chords and harmony in general. There are so many different ways to harmonize a melody with different chords that you could keep busy for a lifetime having fun and being creative!