A chord can be defined as a group of three or more different notes played together. Every chord is based upon a specific formula which relates back to the major scale after which it is named. The formula for a major chord is 1 3 5, hence the C major chord consists of the first, third and fifth notes of the C major scale, i.e., C–E–G.
A chord must contain at least three notes, and any of these three may be repeated. In the F chord illustrated there are two F notes, one A note and one C note.
Now consider the D major chord, which is constructed from the D major scale:
The same major chord formula 1 3 5 applies to all major scales, as demonstrated in the following table. To see all the major scales, see the section on Major Scales earlier in the Appendices.
*The root note is the note after which the chord is named (e.g., C is the root note of the C major chord).