Major vs. minor
A major triad is a root, a major third, and a perfect fifth — it’s the bright, resolved sound behind most pop and folk. A minor triad swaps the major third for a minor third, one fret lower, and the same shape turns sad. That single half-step is the whole difference between a happy chord and a moody one.
Why open shapes look the way they do
An open chord shape is just the fingering that lets a triad ring out across all six strings using open (unfretted) strings wherever possible. Some strings get muted (“x”) because the note they’d ring at isn’t part of the chord. Once you can name the notes in a triad, every open shape you already know stops being a shape to memorize and starts being math you can predict.
From triad to 7th: change one note at a time
Every chord name is a formula counted in semitones from the root. Major is 0–4–7 (root, major third, perfect fifth) and minor is 0–3–7. Lower the fifth of a minor chord by a fret and you get diminished, 0–3–6; raise the fifth of a major chord by a fret and it turns augmented, 0–4–8. A 7th chord keeps its triad and adds one note: a minor 7th (10 semitones) on a major triad makes a dominant 7, a major 7th (11) on a major triad makes a maj7, and a minor 7th on a minor triad makes a m7.
You can watch this happen inside the open E shape, 022100. Its only third is the G# on the G string, first fret. Lift that finger and the open G makes Em (022000). Keep the G# and lift the D-string finger instead: that string was doubling the root, and open D is the minor 7th, so you get E7 (020100). Put that finger on the D string’s first fret, D#, and it becomes Emaj7 (021100). Lift both fingers and it’s Em7 (020000). The A shape, x02220, works the same way: the G string doubles the root (open for A7, first fret for Amaj7) and the B string carries the third (first fret for Am).
Learn which string holds the root, third, and fifth in every shape you already play. Then a new chord symbol tells you which finger to move, and the chord library becomes something you can check against rather than memorize from.
What chord is this?