## Part one

MAIN PRINCIPLES

### III. RULES TO CONSTRUCT SCALES OF AZERBAIJAN MODES

## 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 - 1^{1}/_{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.

**The structure of perfect quarts**

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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