C Major
0 - 4 - 7Root + major 3rd + perfect 5th
About C Major
C major is the chord that theory is written about and the guitar plays awkwardly. On paper it is the simplest thing in Western music — no sharps, no flats, C, E and G. On the fretboard it takes three fingers spread across three frets, and the low E string has to be avoided or muted.
The notes and the missing bass
C, E, G — root, major third, perfect fifth, all natural. The standard shape puts the root on the A string at the third fret, which means the low E below it does not belong to the chord. Strum all six and the lowest note is E, turning C into a chord in first inversion — still C major, but softer at the bottom.
Guitarists deal with this in two ways: mute the low E with the tip of the ring finger, or add G on the low E at the third fret with the little finger. The second is why the four-finger C is worth learning early.
Why it is the reference chord
C major has no accidentals, so it is where notation is taught and where key signatures are counted from. Everything else in the system is described as a distance from here.
On guitar that centrality does not translate. The instrument prefers E, A, G and D, where open strings do the work. C major is the key that theory calls simplest and the guitar calls fourth or fifth easiest — a mismatch worth knowing about when you wonder why a song looks easy on paper and feels awkward under the hand.
Where it shows up
As tonic of its own key, as the IV of G major and the V of F major. In guitar music it is most often met as the IV: G–C–D is one of the first progressions anyone learns, and C is its middle.
Lift the first finger and C becomes Cmaj7; add the little finger at the third fret of the high E and it becomes Cadd9 — the two most common ways songs stay on C for more than a bar without it growing dull.