There are three chord forms that make up the basic guitar chords: the Major form, the Minor form and the Dominant Seventh form. All of these chord forms are derived from the major scales. Once you learn these chord forms, you will be able to figure out and play most rock songs.
You can begin to recognize the different chord forms by the sound they generate. There are some that even classify the chord form by the emotion a chord may evoke when you hear it.
For example, a major chord ‘sounds’ complete, like there are no notes missing. I’ve heard them called “happy” chords, because they just sound full and lively. On the other hand, minor chords have a darker tone to them, almost a “sad” sound. Dominant seventh chords have a bluesy tone to them, kind of an unresolved sound, like you lost something.
Regardless of the chord form, basic guitar chords are built from an established formula of three notes, also called a triad. You have a root note, the third note and the fifth note. The root note is the first note in a scale, the third is – you got it – the third note and the fifth is the fifth note.
So a major chord incorporates notes 1, 3 and 5 of the scale. Since the 1 note is the root note, it might be shown as ‘R’ for root.
A minor chord consists of the root, a flatted third note and the fifth note, notated like this: R, b3, 5
A dominant seventh chord simply adds a flatted seventh note to a major chord. It would be shown like this: R, 3, 5, b7
Since a musical scale is seven notes (at least in western music, which includes rock), we can begin to understand how to create these guitar chords.
To keep it simple, let’s look at the scale of C major. This is the easiest to demonstrate because every note in the scale of C is a major note (the scale itself has no sharps or flats). Here are the notes in the C major scale: C, D, E, F, G, A, B
Using the explanation above (notes R, 3 and 5 of the scale), a C major (C) chord would be the C, E and G notes. A C minor (Cm) chord is the C, Eb (E flat) and G notes. A C dominant seventh (C7) chord is C, E, G and Bb (B flat).
If this seems like way too much theory, don’t worry about it too much. Song tablature (tabs) typically shows you where to place your fingers to form the basic guitar chords. But the better you understand ‘how‘ these chords are formed, the easier it will be to learn and play most guitar chords for rock songs.