Guide to Chord Formation by Howard Wright (Howard@jmdl.com)
Chapter 2 : Intervals
2.0 : Intervals
This is a way of referring to notes by desribing the 'distances'
between them.

G major scale: (Reproduced from chapter 1 for clarity. SB)
Note of the scale Distance up from root note Actual note

1 (root note) 0 G
2 2 semitones A
3 4 semitones B
4 5 semitones C
5 7 semitones D
6 9 semitones E
7 11 semitones F^{#}
8 12 semitones G
In the G major scale above, we can see that the distance between the
1st note (or root note) and the 2
^{nd} note is 2 semitones  this is
called a
2^{nd}.
The distance between the root note (
G) and the 3
^{rd} note in the scale
is 4 semitones  this is called a
3^{rd}.
Pretty easy so far.
All you need to do is count up from the root note using notes of the scale, and if you end up on the 5
^{th} note of the scale you have a 5
^{th}, if you're on the 7th note, you've got a 7
^{th}.
Surely it can't be that simple...?
2.1 : Interval Flavours
Well not quite. As well as
major scales, there are
minor scales. You could also have a 'weird' note or
chromatic note that didn't fit into either scale. To cope with this, the intervals come in different
flavours.
You can have a
minor 3^{rd} or a
major 3^{rd}.
You can have a
normal 5^{th} (
perfect 5^{th}) or an
augmented 5^{th}.
You can have a
9^{th} or a
flat 9^{th}.
All that changes here is that the '
distance' or
interval is either stretched or squeezed by one semitone (half step).
So a minor 3
^{rd} is a semitone less than a major 3
^{rd}.
An augmented 5
^{th} is a semitone more than a perfect 5
^{th}.
You will see a few different terms here which mean the same thing.
 An augmented or sharp interval means one semitone higher.
 A diminished or flat interval means one semitone lower.
You also have minor and major intervals which differ by a semitone  the minor interval is one semitone lower than the major interval.
Here is a table of
intervals with their corresponding 'distances' in semitones.
2.2 : Table of Intervals
Semitones Interval

0 Unison
1 flat 2^{nd}
2 2^{nd}
3 minor 3^{rd}
4 major 3^{rd}
5 perfect 4^{th}
6 flat 5^{th} (diminished 5^{th} or augmented 4^{th})
7 perfect 5^{th}
8 minor 6^{th} (or sharp 5^{th}/augmented 5^{th})
9 major 6^{th}
10 minor 7^{th} (flat 7^{th})
11 major 7^{th}
12 octave
13 flat 9^{th}
14 9^{th}
15 sharp 9^{th}/minor 10^{th} (just minor 3^{rd} one octave higher)
16 major 10^{th} (just major 3^{rd} one octave higher)
17 11^{th}
18 augmented 11^{th}
19 perfect 12^{th} (octave above perfect 5^{th})
20 flat 13^{th}
21 13^{th}
So to work out any particular note, say the major 6
^{th} of an
A major
scale, start with
A, find the distance for a major 6
^{th} (9 semitones)
and just count up from A.
You should end up with
F^{#}, so this is a major 6
^{th} up from A.
(see
chromatic scale 
Appendix A).
So, to
recap. Chords are described or '
spelled out' using
intervals.
These intervals tell you far above the
root note the other
notes of
the
chord are. By using the
table above you can find out how many
semitones you need to move up for any given interval.
Here is a simple example.

Bm7  the spelling for this is: 1^{st}, minor 3^{rd}, 5^{th}, minor 7^{th}.
Start with B  count up 3 semitones for a minor 3^{rd}  you get D.
Count up 7 semitones from B to get the 5^{th}  F^{#}.
Count up 10 semitones to get the minor 7^{th}  A
So the notes are: B D F^{#} A
So  if you know the
spelling of a particular chord (i.e. the
intervals which describe it) then it's simple to use the table
above to find out what notes you need.
What if you don't know the chord spelling?
If you just have a chord name, like
F^{#}m9, then you need to
know how this chord is built.
The basic building blocks of
all chords are
triads.
Guide to Chord Formation by Howard Wright
Reformatted and noded (with permission) by Space Butler
< Introduction 
Index 
Triads >