When I was a kid, which was very recently — in fact I don’t know why you would suggest it was not recently — in fact I’m not even 40 yet — , I learned tons of chord shapes for the guitar. We started with the “cowboy” chords (the chords in the 1st position that use lots of open strings) and moved on to the barre chord forms. The barre chords are often just the cowboy chords moved up to higher positions, and with the open strings barred. From there, I learned the “jazz” chords (the 7ths, 9ths, 11ths, and 13ths), mostly from the perspective of modifying barre chords to get the additional scale degrees.
Only years later did I learn what I call the “piano” chords: the 3-note chords played on strings ④, ③, and ②. In retrospect, I wish I had learned the piano chords first, for several reasons:
I have written out below a charts of the triads (major, minor, augmented, and diminished) and the 7th chords (major 7, minor 7, dominant 7, and diminished 7). Yes, I left augmented 7 out as an exercise for you!
How To Read These Charts: I have diverged somewhat from the standard. First, I don’t show any fingerings; I think you’ll find that these shapes lend themselves naturally to 1 or 2 fingerings.
Second, I use a hollow circle to indicate the root note. For example, in this major chord shape:
the note on the ④th string is the root note. Say you are playing this chord in the fifth (V) position: you’d play the ④th string at the VIIth fret, the ③rd string at the VIth fret, and the ②nd string at the Vth fret. The note on ④ at the VIIth fret is A, so you’d have an A major chord. Move the whole shape down 1 fret to get an A♭ major (also known as G♯ major), or move the whole shape up 1 fret to get an A♯ major (also known as B♭ major).
Third, the 7th chords have 3 filled circles and 1 hollow circle, with the hollow circle on the same string as 1 of the filled circles. To play these chords, do not play the hollow circle note. It is only there to show you where the root note of the chord is. In fact, the root note is not played! That is OK, because the bass will usually play the root note at least once during the lifetime of the chord.
Consider, for example, this 7th chord shape at the Vth position (like before):
You would play ④ at the VIth fret (the hollow circle at VII is the root, but don’t play it!), ③ at VI, and ② at V. That’s an A major 7 chord. (Try playing the open ⑤, an A, to get a root note!)
Whew! That’s plenty for now. Maybe in a later post I’ll show some further piano chords. It’s fairly easy to take these core shapes and get 6th chords, suspended chords, and stranger things.