Chord Construction
All chord types are based upon a unique formula which relates back to the major scale which has the same letter name as the chord, e.g., C chords are based upon a formula that is applied to the C major scale. Here is the C major scale written in standard music notation and tab (tablature). If you play these notes you would get the familiar Do Re Mi Fa So La Ti Do sound.
The letter name of each note is written below the note on the staff (3). The number written below the letter name is the degree number of the note in the scale. These thirteen note degrees are all that is needed to create all chord types. Each chord type will have its own unique formula.
C
The formula for the major chord is 
which means that the major chord consists of the first, third and fifth notes of the major scale. For example, the C major chord consists of the 1st, 3rd and 5th notes of the C major scale i.e., the notes C E G. These notes can be in any order and can be duplicated, although there must be at least one of each. For example, in the following diagram of the C major chord shape there are two C notes, three E notes and one G note. The G major chord consists of the 1st, 3rd and 5th notes of the G major scale, i.e., the G B D notes.
The formula for a minor chord is 
which means that the minor chord consists of the first, flattened third and fifth notes of the major scale. For example, the C minor (Cm) chord consists of the 1st, 3rd and 5th notes of the C major scale, i.e., C Eb G. So even though it is a minor chord the chord formula still relates back to the major scale.
The chord formula chart in the next section lists all the chord types in this book along with its formula (relative to the major scale) and an example based upon C. A full understanding of chord construction is very useful as your playing ability advances as it is particularly useful when improvising, substituting or writing an accompaniment for a song or piece of music.
You will need to know about major scales, keys, key signatures, sharps(#) and flats (b). All this information and everything you need to know about useful theory for guitar can be found in Progressive Guitar Method : Theory
