This is by no means an attempt to fully explain music theory. However, it can be used as a reference for building simple chords.
The basic music scale is made up of series of 12 notes, each separated by a semitone (S). A tone (T) is 2 semitones. Depending on where you start, the notes look like this:-
| A | A# | B | C | C# | D | D# | E | F | F# | G | G# |
| B | C | C# | D | D# | E | F | F# | G | G# | A | A# |
| C | C# | D | D# | E | F | F# | G | G# | A | A# | B |
| D | D# | E | F | F# | G | G# | A | A# | B | C | C# |
| E | F | F# | G | G# | A | A# | B | C | C# | D | D# |
| F | Gb (F#) | G | Ab (G#) | A | Bb (A#) | B | C | Db (C#) | D | Eb (D#) | E |
| G | G# | A | A# | B | C | C# | D | D# | E | F | F# |
| etc |
Based on the starting note, these notes can be identified by their position in the scale.
| 1 | b2 | 2 | b3 | 3 | 4 | b5 | 5 | b6 | 6 | b7 | 7 |
Chords are created by selecting certain variations on these positions. Here is a list of the simplest chord:-
| major | 1 | 3 | 5 | |
| minor | 1 | b3 | 5 | |
| 7th | 1 | 3 | 5 | b7 |
| minor 7th | 1 | b3 | 5 | b7 |
| major 7th | 1 | 3 | 5 | 7 |
| 6th | 1 | 3 | 5 | 6 |
So, for instance if we want to work out all of these chords for the scale starting at D, we get:-
| 1 | b2 | 2 | b3 | 3 | 4 | b5 | 5 | b6 | 6 | b7 | 7 |
| D | D# | E | F | F# | G | G# | A | A# | B | C | C# |
| D major | D | F# | A | |
| D minor | D | F | A | |
| D 7th | D | F# | A | C |
| D minor 7th | D | F | A | C |
| D major 7th | D | F# | A | C# |
| D 6th | D | F# | A | B |
or for G
| 1 | b2 | 2 | b3 | 3 | 4 | b5 | 5 | b6 | 6 | b7 | 7 |
| G | G# | A | A# | B | C | C# | D | D# | E | F | F# |
| G | G | B | D | |
| G minor | G | Bb (A#) | D | |
| G 7th | G | B | D | F |
| G minor 7th | G | Bb (A#) | D | F |
| G major 7th | G | B | D | F# |
| G 6th | G | B | D | E |
So, by knowing the starting note, and which intervals make up the chord, eg - major = 1-3-5, the notes of any chord can be worked out.