Mind, Body, World- Foundations of Cognitive Science, 2013a

The musical notation for the C major scale is provided in the sequence of notes
illustrated in the first part of Figure 4-8. The Greeks defined a variety of modes for
each scale; different modes were used to provoke different aesthetic experiences
(Hanslick, 1957). The C major scale in the first staff of Figure 4-8 is in the Ionian
mode because it begins on the note C, which is the root note, designated I, for the
C major key.
One can define various musical chords in the context of C major in two different
senses. First, the key signature of each chord is the same as C major (i.e., no
sharps or flats). Second, each of these chords is built on the root of the C major scale
(the note C). For instance, one basic chord is the major triad. In the key of C major,
the root of this chord—the chord’s lowest note—is C (e.g., piano key #1 in Figure
4-7). The major triad for this key is completed by adding two other notes to this
root. The second note in the triad is 4 semitones higher than C, which is the note
E (the third note in the major scale in Figure 4-8). The third note in the triad is 3
semitones higher than the second note, which in this case is G (the fifth note in the
major scale in Figure 4-8). Thus the notes C-E-G define the major triad for the key
of C; this is the first chord illustrated in Figure 4-8.
A fourth note can added on to any major triad to create an “added note” tetrachord
(Baker, 1982). The type of added note chord that is created depends upon
the relationship between the added note and the third note of the major triad. If
the added note is 4 semitones higher than the third note, the result is a major 7 th
chord, such as the Cmaj7 illustrated in Figure 4-8. If the added note is 3 semitones
higher than the third note, the result is a dominant 7 th chord such as the C7 chord
presented in Figure 4-8. If the added note is 2 semitones higher than the third note,
then the result is a 6 th chord, such as the C6 chord illustrated in Figure 4-8.
The preceding paragraphs described the major triad and some added note
chords for the key of C major. In Western music, C major is one of twelve possible
major keys. The set of all possible major keys is provided in Figure 4-9, which
organizes them in an important cyclic structure, called the circle of fifths.
F
C
G
A#
D
D#
A
G#
E
C#
F#
B
Figure 4-9. The circle of fifths.
Elements of Connectionist Cognitive Science 163