A chord is three or more different notes played as one unit.
The smallest and most basic chord you can build is a triad, or three-note chord.
There are four different types of triads:
Major
Minor
Diminished
Augmented
All chords in tertian harmony contain some type of triad. Any other type of chord (seventh, ninth, etc.) has the same character as the basic triad which it contains (major, minor, etc.).
We use every other note of the scale to build chords.
Starting with the first note of the major scale as the root of the chord, skip the second degree of the scale and move on to the third degree, making that the 3rd of the chord. Then skip the fourth degree, and use the
fifth degree of the scale for the 5th of the chord (the final note of the triad).
To get a C major chord, use a C major scale. To get a G major chord, use a G major scale.
The notes of a C major chord are C, E, and G, or 1, 3, and 5, respectively.
Major triads can be used as I, IV, or V chords in the blues, but most often you will turn them into sevenths, ninths, or other extended chords, (see in the next chapters). Major triads are used extensively though in rock and R&B styles, again most often as I, IV, or V chords.
Minor triads are built exactly the same way as major triads but with one important difference-we use a different scale. Just as we used a major scale to build any type of major chord, we use a natural minor scale to build any kind of minor chord.
The notes of a C minor chord are C, Eb, and G, or 1, 3, and 5, respectively.
Since we are relating all notes to the major scale, we say the minor triad has a flatted 3rd.
Minor triads are used in the same way as major triads, but in minor keys. They can also be used as secondary chords in a major key (see Blues You Can Use).
The simplest way to build a diminished triad is to take a minor triad, and flat the 5th - lowering the 5th of the chord one half step (one fret). Using the C minor triad we just built, we'll lower the G (5 of the C minor chord) and make it a Gb (b5).
The a diminished triad functions in a fairly unusual way in a blues progression. Usually it's not actually chord of the key. More often it's used as a passing chord which passes from one chord in the key to another. It makes the chord movement stronger or smoother, or both. As with the major and minor triads, diminished chords are most often made into seventh chords for use in the blues. We'll see how to use them a little later.
Augmented chords are most often used as the V chord in a blues progression. They have a very distinctive sound. They stand out and make the chord progression stronger when used in moderation. They are usually found at the end of the chord progression, making the return to the top of the cycle (or end of the song) stand out.
The root does not have to be the bottom, or bass note, of a chord form. When it is in the bass, the chord is said to be in root position.
However, any one of the other notes of the chord can be in the bass. If a note other than the root is in the bass, it is called an inversion. If the 3rd of the chord is in the bass, it is called first inversion. If the 5th of the chord is in the bass, it is called second inversion.
A triad is made up of only three notes, but does this mean you can only use three strings to play a major oror minor triad? The answer is no.
You can double any or all of the notes. By this we mean you can play the root, 3rd, or 5th of a triad (or any note of a chord, for that matter) in two or more places. The doubled notes will be an octave or two apart and will only count as one note because their function is the same within the chord.
Doubling lets you build a fuller sounding chord. You'll see sometimes you can have the same note on three different strings in a chord. This is still called doubling even though it is actually tripled.
When learning chords on the guitar, a useful approach is to study generic triad forms - shapes that work across strings tuned in consistent intervals (like the 3rd, 4th, and 5th strings). However, because the 2nd string (B) is tuned differently (a major 3rd above the 3rd string instead of a perfect 4th), these shapes may require slight adjustments when crossing over to the 1st and 2nd strings.
When playing the generic chord forms across the fretboard, you need to compensate for the 2nd string tuning difference, and change fingering as appropriate:
Open voicings use non-consecutive strings, skipping and muting a string or two in the middle. They're nice and clean sounding with the notes spread further apart. You'll find they're good for situations where other instruments are also playing chords.
The preceding chords can be combined to make larger voicings, making use of doubling. The following chord forms are not all the larger forms you can use, but they are useful in playing blues and blues-based music.
Notice we don't include diminished or augmented chords here. This is because we don't often double notes in diminished triads; we'll look at some doubling in augmented chords next. Notice some voicings work well for major triads but not for minor, and vice versa.