What is a chord?

Definition: A chord is a combination of three or more different notes. They may be played at the same time or sequentially. CHORD is just the relation between notes, played more or less at the same time. FULL STOP.

So we have to learn the rules. Once we know the rules we can use them, or we can break them, which is a very interesting experience.

• Chords can be built by stacking triads. As there are two triads for the simple three-note chords there are four possible chords: major, minor, diminished and augmented.

• The  most common three-note chord are made with major thirds and minor thirds. These chords have the interval structures major=1 3 5, minor=1 b3 5, diminished=1 b3 b5 

• The sequence of the three notes does not change the name.

Chord Scale Relationships

You can know all the chords in the world, but if you don't know how or when to use them over a scale, they really mean nothing. If you're a beginner or intermediate keyboard player you may well find it hard to find one chord that will fit over that scale. The relationship between the vertical usage of a scale is chords (harmony), and the horizontal usage of a scale is the melody. 

The first step is to learn how to build chords. What we're going to learn in this lesson is how to put the right chord to the correct scales or vice-versa. Basically, when the melody notes and chords come from the same scale they generally sound good together, but if the melody and chords come from different scales it sounds not so melodic.

Let's start with the melodic stuff. What we're going to do is get the C major scale and build triads (three note) on each note of the scale. If you play already, you probably know that a three-note chord is called a triad and that it has a root, third and fifth tone. As you can see the triad contains the notes C, E, G - the C major triad. This is known as the I chord. We use Roman numerals to label the chord number. The second (II) triad has D, F, A which is a D minor triad. The III chord has E, G, B, which is Emi7. The IV chord contains F, A, C, which is F major. The V chord contains G, B, D which is G major chord. The VI chord contains A, C, E which is A minor. The VII chord contains the B, D, F which is a B diminished chord.

So, all these chords belong to the key of C major. Therefore, the C major chord can be played over the top of  C major scale. Since every major scale has the same scale pattern, the chord patterns will remain the same. The I chord is major, the II chord is minor, the III chord is minor, the IV chord is major, the V chord is major, the VI chord is minor, the VII chord is diminished. (See Example 2 for triads in G major)

Basically, this is where chord progressions come from. Let's make up a I, V, VI, IV chord progression in the key of C major (see example below). Play these chords over the C major scale, D major scale, E major scale, F major scale ...... and so on.

What chords are in what Scale, and why? 

Basic Triads. (triads means three notes chord)

Each diatonic scale has 7 different notes, which gives way to 7 possible triads for each key in music. A triad is the 1st, 3rd, and 5th notes of a scale played simultaneously to form a chord.

All chords are formed based on their respective major diatonic scale. A  C chord is built on a C major scale, a D chord is built on a D major scale, etc.

There are 7 chords for each key, which correspond to the 7 notes in each key's scale. Some chords can be in more than one key - for example, a D major chord can be in the keys D, A, or G.

I'll use the key of C as an example. You may use any major key like Cmaj, Dmaj, Emaj .....etc,

The key of C includes the notes C D E F G A B C.
Each note of the scale corresponds to a scale degree as shown:

       ..Note:    C D E F G A B C
       Degree:  1 2  3 4  5  6 7 1

You can form 7 basic chords (triads) from the notes in the key of C. Each different note is the root of a different chord.

There are 3 combinations of the 1st, 3rd, and 5th notes that will be covered in this lesson. There are 3 more, but they are not included.

       Major triad: 1 3 5
       Minor triad: 1 b3 5
       Diminished triad: 1 b3 b5

Your first chord will be a C chord, because C is the first scale degree. Now, since this is a C chord, it will be based on the C major diatonic scale. Take scale degrees 1 3 5 as shown below:
       ..Note:   C D E F G A B C
       Degree: 1  2  3 4  5  6 7  1

This gives you notes C, E, and G. Since all 3 of those notes are in the key of C, you do not have to modify them to fit, and you have a major triad (1 3 5). So your first chord is C major.

The second chord will be a D chord, because D is the 2nd scale degree. It's based on the D scale, which is D E F# G A B C# D. Now, take 1 3 5 of this scale:

       ..Note:   D E F# G A B C# D
       Degree: 1  2  3   4  5  6  7   1
.
This gives notes D F# A. This presents a problem - F# is not in the key of C! In order to keep this chord in key, we have to flat the F# (lower it by 1/2 step) down to F natural. This gives D F A, which is scale degrees 1 b3 5 of the D major scale. 1 b3 5 is the formula for a minor triad. Therefore, your second chord is D minor.

The seventh chord will be a B chord, because B is the 7th scale degree. It's based on the B scale, which is B C# D# E F# G# A# B. Now, take 1 3 5 of this scale:
      

       ..Note:   B C# D# E F# G# A# B
      Degree: 1   2   3   4   5   6    7   1

This gives notes B D# F#. D# (3) and F# (5) are not in the key of C, and must be flatted to D (b3) and F (b5), respectively. This gives us scale degrees 1 b3 b5, which is the formula for a diminished triad.

Based on these examples, you can figure out the rest of the chords. However, they always follow a pattern:
 1 - major
 2 - minor
 3 - minor
 4 - major
 5 - major
 6 - minor
 7 - diminished

By applying this pattern, you can quickly figure out that the chords in the key of C are:

 Cmaj
 Dmin
 Emin
 Fmaj
 Gmaj
 Amin
 Bdim

All the notes contained in the above chords will be in the key of C.

This pattern works for any of the keys in the Circle of 5ths. It does not, however, cover any scales that are not the major scale (such as the harmonic minor scale, for example. That has its own pattern of chords).  

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