Music theory part 2

This is the second music theory post and we will discuss intervals and chords. An interval is basically the distance between two notes as measured in semitones (see my first music theory post for a definition of a semitones). If you remember the table of modes from my previous post (shown below), there is roman numeral for each of the scales and that represents the interval from the tonic (the note C) to the starting note in the scale. These roman numerals will also come into play when I talk about chords.

So if we look at the C major scale and the corresponding roman numerals:

C D E F G A B C
I II III IV V VI VII I

The interval from C to the other notes are:

C is unison at zero semitones
D is the second at two semitones
E is the third at four semitones
F is the fourth at five semitones
G is the fifth at seven semitones
A is the sixth at nine semitones
B is the seventh at eleven semitones
C is the octave at twelve semitones

If we look at the minor scale and remember from the circle of fifths that A minor contains the same notes as the C major scale, we have the following notes

A B C D E F G A
I II iii IV V vi vii I

A is unison at zero semitones
B is the second at two semitones
C is the minor third at three semitones (designated by lowercase roman numeral)
D is the fourth at five semitones
E is the fifth at seven semitones
F is the minor sixth at eight semitones
G is the minor seventh at ten semitones
A is the octave at twelve semitones

Why do the third, sixth and seventh intervals have a minor in their name? Because they have a different number of semitones in the interval than the third, sixth, and seventh in the major scale and because they are the notes in a minor scale they are defined as minor third, minor sixth, and minor seventh. The second, fourth, and fifth are not minor intervals because they have the same number of semitones as in the major scale. The fourth and fifth are special in that they maintain the same number of semitones whether the scale is major (Ionian and Mixolydian modes) or minor (Aeolian, Dorian, or phrygian). That is why they are called perfect intervals. The other intervals are either major or minor depending on the mode. The table below shows the intervals that are contained in the seven diatonic scales.

In two of the scales (Lydian and Locrian) you see that the fourth is augmented and the fifth is diminished. Augmented means that the interval is one semitone higher ( also called raised a semitone) and diminished means the interval is one semitone lower (also called lowered a semitone).

Chords

Chords are made from at least three notes. The first common chord is the major chord. The major chord contains the root note, the third above the root and the fifth above the root. The root identifies the chord. For example the G major chord (commonly called just a G chord) is made up of the following notes.

G B D
I III V

To get any other major chord you just take the root, the third, and fifth note from the corresponding major scale. The other commonly used chord is the minor chord. This is similar to the major chord except you use the minor third in place of the major third. If we look at the G chord again but make it a G minor (Gm), it contains the following notes

G Bb D
I iii V

Like the major chord, you can form any minor chord by taking the root, the third, and fifth note from the corresponding minor scale. OK that's cool you say but are there other chords? Yes, you can add other notes from the scale to form more chords and here are some of the common ones:

Seventh chord: this contains the root, the third, the fifth and the minor seventh
Minor seventh: this contains the root, the minor third, the fifth, and the minor seventh
Major seventh: this contains the root, the third, the fifth, and the seventh
Diminished chord: this contains the root, the minor third, and a diminished fifth
Augmented chord: this contains the root, the third, and an augmented fifth

The other set of chords that I will discuss are the ninth, eleventh, and thirteenth chords. Hey wait... The intervals only go up to seven, how can you have a ninth chord. Well the scale is cyclical so if you continue counting beyond the octave note you can get a ninth interval and that is the same note as the second interval. So this set of chords take the seventh chords and add a ninth (second), eleventh (fourth), or thirteenth (sixth) note to the chord. Below is a table that shows the construction of these chords

So those are the common chords use see used in songs. The last thing I will discuss is chord progressions. This is the series of chords that are formed by using the notes of a scale but having the root note be each note in the scale. For example in the C major scale, the notes are

C D E F G A B C

What is the C chord that fits in the scale, same with the D chord, and so on. Well the progression of chords is

Major - minor - minor - major - major - minor - minor diminished

For the C major scale that is C - Dm - Em - F - G - Am - Bm(dim)

Using roman designation again the progression is

I ii iii IV V vi vii(dim)

So we have the same relationship between chords and we do with notes. So in the key of C the Em chord is the minor third of the C chord.

So hopefully this will give you enough background on intervals and chords so you can follow along as I discuss the creation of my songs. Enjoy...

-Ron-

[Edit 7/17/11]
I forgot to add that all figures in this post were provided by Wikipedia