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A.
Scales of the main modes
It is evident clear that tetrachords that forming the bases
of the Azerbaijan modes' scales represent the following varieties:
1 - 1- 1/2 main
1 - 1/2- 1 auxiliary
1/2 - 1- 1 auxiliary
1/2 - 1- 1/2 diminished
1/2- 11/2 - 1/2
with an increased second.
All
above five tetrachords may theoretically be combined by all
four ways of combination, introduced in the previous chapter.
However not all the 20 scales obtained as a result of these
combinations would be suitable to form Azerbaijan modes. The
scales, intended to form main Azerbaijan modes should meet two
basic requirements:
1)
Strict consequent construction order, i. e. the scales should
consist of perfect
quarts, or perfect quints, or minor or major sixths' gradual
succession.
2) The grades of scales should not form tritons.
To
construct the scales of main Azerbaijan modes one has to chose
a tetrachord. Perfect quarts or perfect quints should be formed
from each grade in ascending or descending directions. The scales
received could be a basis to construct one of the main Azerbaijan
modes. The condition is the lack of tritone.
Scales formed by the combination of main tetrachords according
to formula 1 - 1- 1/2.
Structure
of perfect quartes
If
perfect quarts are constructed from each grade of the main tetrachord
(1 - 1- 1/2), we receive a scale consisting
of successive perfect quarts, for instance:
This
scale consists of two equal tetrachords 1 - 1- 1/2,
combined by the first way of combination (conjoint). This scale
is the basis for Azerbaijan mode "Rats".
The
structure of perfect quints
If
perfect quints are constructed from each grade of the main tetrachord,
we receive a scale consisting of successive perfect quints:
This
scale could not be the basis for Azerbaijan mode due to tritone
(see example 20).
The
structure of minor sixths
If
minor sixths are constructed from each grade of the main tetrachord,
we receive a scale consisting of successive minor sixths, for
instance:
This
scale consists of two equal main tetrachords built on the formula
1 - 1- 1/2, combined by the third way
of combination (by an intermediate semitone). It may be the
basis for "Bayati-Shiraz" mode.
The
structure of major sixths
If
major sixths are constructed from each grade of the main tetrachord,
we receive a scale, consisting of successive major sixths:
This scale could not be the basis for Azerbaijan mode, due to
two (!) tritones are available.
All
above clarifies that the main tetrachord as a basis to scales
of Azerbaijan modes may be combined only by the first and the
third ways of combination.
Scales
formed by the combination of equal auxiliary tetrachords (1
- 1/2 - 1)
The
structure of perfect quarts
If
perfect quarts are constructed from each grade of the auxiliary
tetrachord (1 - 1/2 - 1), we receive a
scale consisting of successive perfect quarts, for instance:
This
scale consists of two equal tetrachords 1 - 1/2
- 1, combined by the first way of combination (conjoint). This
scale is the basis for Azerbaijan mode "Shur".
The
structure of perfect quints
If
perfect quints are constructed from each grade of the auxiliary
tetrachord, we receive a scale consisting of successive perfect
quints:
This
scale could not be the basis for Azerbaijan mode due to tritone.
The
structure of minor sixths
If
minor sixths are constructed from each grade of the auxiliary
tetrachord, we receive a scale consisting of successive minor
sixths, for instance:
This
scale consists of two equal main tetrachords built on the formula
1 - 1/2 - 1, combined by the third way
of combination (by an intermediate semitone). It may be the
basis for "Navva" mode. The latter is used very seldom.
The
structure of major sixths
If
major sixths are constructed from each grade of the auxiliary
tetrachord, we receive a scale, consisting of successive major
sixths:
This scale could not be the basis for Azerbaijan mode, due to
two tritones are available.
All
above clarifies that the main tetrachord as a basis to scales
of Azerbaijan modes may be combined only by the first and the
third ways of combination.
The
structure of perfect quarts
If
perfect quarts are constructed from each grade of the auxiliary
tetrachord (1/2 - 1 - 1), we receive a
scale consisting of successive perfect quarts, for instance:
This
scale consists of two equal tetrachords 1/2
- 1 - 1, combined by the first way of combination (conjoint).
This scale is the basis for Azerbaijan mode "Segakh".
The
structure of perfect quints
If
perfect quints are constructed from each grade of the auxiliary
tetrachord, we receive a scale consisting of successive perfect
quints:
This
scale could not be the basis for Azerbaijan mode due to tritone.
The
structure of minor sixths
If
minor sixths are constructed from each grade of the auxiliary
tetrachord, we receive a scale consisting of successive minor
sixths, for instance:
This
scale consists of two equal main tetrachords built on the formula
1/2 - 1 - 1, combined by the third way
of combination (by an intermediate semitone). It may be the
modulation formula for transition from one mode to another.
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