Chord construction becomes manageable once three terms are clear. The root is the note that names the chord, an interval is a measured distance from that root, and a triad is a three-note chord.
Musicians often build basic chords by taking every other note from a scale. In C major, starting on C and selecting C, E and G produces a C major triad.
Major triad: 1-3-5
A major triad contains the root, major third and perfect fifth. From C, those notes are C, E and G. The major third is four semitones above the root and gives the chord its major quality.
Minor triad: 1-flat 3-5
Lower the third by one semitone and the chord becomes minor. C minor contains C, E-flat and G. The root and fifth stay the same; the changed third creates the new quality.
Diminished and augmented triads
A diminished triad lowers both the third and fifth: 1-flat 3-flat 5. An augmented triad keeps the major third and raises the fifth: 1-3-sharp 5. These interval formulas work from any root.
Seventh chords and extensions
Adding another third above the triad creates a seventh chord. Continuing the process can produce ninths, elevenths and thirteenths. The full chord symbol tells you which intervals are major, minor, perfect, lowered or raised.
Why guitar shapes repeat or omit notes
A six-string voicing may double the root or fifth in another octave, and complex chords often omit less important tones because the hand and instrument have limited space. The chord name describes the harmonic functions, not the number of strings sounding.
How to read the formula on the fretboard
Start from a known root and count semitones to each required interval. On one string this is easy to see; across several strings, note names and interval shapes help you place the same formula in compact voicings.
Put the idea on the fretboard
- Write the notes of one major scale, such as C-D-E-F-G-A-B.
- Select the first, third and fifth notes to create the major triad C-E-G.
- Lower the third by one semitone to create C-E-flat-G, a C minor triad.
- Find those notes in a small three-string voicing and play them separately before playing them together.
- Compare the note formula with a familiar open chord and identify which notes are repeated.
When the idea still feels confusing
Terms such as third and fifth feel abstract
Count from the root through the letter names and also count frets. Use one key until the sound becomes familiar.
You expect every guitar shape to show only three strings
Triads use three note names, but guitar voicings often repeat those notes in several octaves.
You think any added note creates a ninth or eleventh chord
Extensions are normally named in relation to a seventh chord. An added note without a seventh is often called add9 or add11.
The guitar shape contains repeated notes
That is normal. A six-string voicing often doubles the root or fifth in another octave. Chord construction is based on distinct pitch functions, not the number of strings sounding.