Triads & 7ths in Every Key in Chord Symbols
Upper case Roman numerals are Major, lower case are minor. Lower case with a degree sign is diminished.
In all Major keys:
I, IV, V are Major
ii, iii, vi are minor
viio is diminished
We have a lot of choices on how we play [voice] these chords on the guitar. Over time, each of us builds preferences for the way we voice chords. Some chords are easier to finger than others, plus some ring out with certain sound-shapes that we prefer. Also, styles determine the types of voicings we may choose.
One way to apply this list is to play chord scales. This is playing chords alphabetically, ascending and descending, as we play scales.
We also play progressions. We choose a progression such as I-vi-ii-V and play it in any or every key.
7th chords are 4 tone chords. They are taking chord building every other note [EON] until we have 4 tones. We have a root, some type of 3rd, 5th, and 7th.
In a Major key, the 7th type chords are…
I & IV are Major 7 types. The 7indicated Major 7. You may also see M7 or Maj7. These are Major triads with a Major 7. The Major 7 is an interval of 11 half steps [half step below the root of the chord].
The V is a Dominant 7. It is indicated by just a 7. The V7 is a Major triad with a minor 7. The minor 7 is an interval of 10 half steps [2 half steps below the root of the chord].
The ii, iii, and vi are minor 7. You may also see min7 or -7. These are minor triads with a minor 7.
The vii is minor 7, flat 5. This is a minor triad with a flat 5, and a minor 7. This chord is also known as half-diminished.