In this final lesson of the course we take our harmonised key of C major and add the correct 7th chords to the correct degrees within the scale. Once again, this involves us learning a formula that you can then apply to any major key!
Just as we did when we harmonised the key of C major to triads, we can now dot he same with 7th chords. The process is the same, you create the chord using just the notes in the C major scale. So, for example, when looking at D (The second degree of the scale) we know that a Dm fits in (using the notes D, F & G) and now we can use Dm7 as well because that has D, F, G & C in it, which are all notes from the C major scale. On the other hand, D7 wouldn't work here because it has D, F#, A & C. The F# is clearly not in the C major scale and therefore cannot be used. This is the process for each chord.
Once we have been through the process we are left with another formula to remember, which is as follows:
To help you put this into practice, here is a common way to play all 7 chords on the guitar. Try to put all of them together in this key (C major) to hear how they work together. Try to also refer to them as "first degree, 2nd, 3rd..." etc.
You've now completed and taken a huge step forwards in your guitar playing journey.
Feel free to bask in glory for a while, or go ahead and try another course if you're hungry for more.