You’re on the right page if you’re interested in learning about 9ths, 11ths, and 13ths.
Coming across 9ths, 11ths, and 13ths are inevitable while studying chords, and this is because beyond the level of triads and seventh chords are extended chords — which are classified into 9th chords, 11th chords, and 13th chords.
The formation of these extended chords require what music scholars call extensions.
Now for the sake of those who are just coming across the term extension for the first time, we’ll be getting started with this study by taking a look at what extensions are.
“What Are Extensions?”
The Ninth Extension
The ninth extension is exactly the ninth scale tone in the major key; starting from the first tone of the scale. For example, using the C major (two octaves) as a reference:
C D E F G A B C D E F G A B C
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
The ninth tone from C:
…is D:
Attention: Keep in mind that D is also the second tone of the C major scale.
The ninth extension can be associated with the second tone of the scale and this is because in the key of C major (which is our reference):
…the ninth extension which is D:
…has the same letter name with the second tone of the scale (which is also D):
Both of them are just an octave apart from each other.
“So, How Do You Determine The Ninth Extension In Any Given Key?”
Using the second tone of the scale (in the key you’re in), you can determine the ninth tone. For example, in the key of Ab major:
…where the second tone is Bb:
…an octave above the second tone (which is also Bb):
…is the ninth extension.
Altogether, a ninth from Ab is Bb:
The Eleventh Extension
Using the C major (two octaves) as a reference:
C D E F G A B C D E F G A B C
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
…the eleventh extension can be determined.
The eleventh tone from C:
…is F:
Attention: It is important to note that F is also the fourth tone of the C major scale.
The eleventh extension can be associated with the fourth tone of the scale and this is because in the key of C major (which is our reference):
…the eleventh extension (which is F):
…has the same letter name with the fourth tone of the scale (which is also F):
Both of them are just an octave apart from each other.
“So, How Do You Determine The Eleventh Extension In Any Given Key?”
The fourth tone of the scale (in the key you’re in), is associated with the eleventh tone. For example, in the key of E major:
…where the fourth tone is A:
…an octave above the fourth tone (which is also A):
…is the eleventh extension.
Altogether, an eleventh from E is A:
The Thirteenth Extension
The thirteenth extension is exactly the thirteenth scale tone in the major key; starting from the first tone of the scale. For example, using the C major (two octaves) as a reference:
C D E F G A B C D E F G A B C
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
The thirteenth tone from C:
…is A:
Attention: Keep in mind that A is also the sixth tone of the C major scale.
The thirteenth extension can be associated with the sixth tone of the scale and this is because in the key of C major (which is our reference):
…the thirteenth extension which is A:
…has the same letter name with the sixth tone of the scale (which is also A):
Both of them are just an octave apart from each other.
“So, How Do You Determine The Thirteenth Extension In Any Given Key?”
Using the sixth tone of the scale (in the key you’re in), you can determine the thirteenth tone. For example, in the key of B major:
…where the sixth tone is G#:
…an octave above the sixth tone (which is also G#):
…is the thirteenth extension.
Altogether, a thirteenth from B is G#:
Final Words
The ninth, eleventh, and thirteenth extensions are associated with the second, fourth, and sixth tones of the major scale and this makes it easy for the extensions to be recalled or determined.
Now that we’ve covered these extensions and how they are derived in this basic lesson, it is recommended that you proceed into the determination of these extensions in any of the 12 major keys.
See you in the next lesson.
Chuku Onyemachi
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