[re]

> While it's almost always I, IV, V, and vi, we have both II or ii, and III or iii, differing on whether the third is major or minor. One way to handle this is just to drop the third from all the chords and play them open

Note that what jefftk calls "open chords" are more commonly called "power chords" (or "indeterminate" or "no3" or "5" chords). This is a distinct concept from the open/"zombie" chords that that youtube video is about. (But if you did use only power chords when covering songs, they would also usually sound quite dull!)

https://en.wikipedia.org/wiki/Power_chord

https://en.wikipedia.org/wiki/Open_chord

[jefftk]

I've now edited the post to say "chords without thirds" instead of "open chords", which should reduce this confusion