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Music theory book

Tonality and modulation

11.1 Tonality

It is not difficult to work out the key of a piece of music. All that is necessary is to look at the key signature and to name the two possible keys; the major and the relative minor. Nonetheless there are some cases where there may be difficulty saying for certain whether a piece is in the major or the relative minor represented by a key signature. In these cases, after having determined the two possible keys (major or minor) one must analyse the first few bars of the piece taking the following factors into consideration.

1) The presence of the tonic triad or tonic note.
We proceed by verifying the presence of the notes belonging to the tonic chord of both tonalities, whether in the melody or the accompaniment. Another indication may be the persistent presence of the tonic note. (In the example from Schumann, the tonic chord of D major appears repeatedly).
Capitolo 12 esempio 1
Example in Braille
Example 1 in D major ( Schumann "Papillons op.2 finale")

2) The presence of a sharpened leading note.
In a major scale the leading note is a semitone from the tonic and this close proximity creates a sense of natural resolution from leading note to tonic. In a minor scale, however, the leading note is a tone away from the tonic and so there is not the same feel of natural resolution. For centuries now composers in the Western tradition have sharpened the leading note in minor scales in order to achieve this sense of natural resolution in those scales as well. This also makes the dominant chord a major triad rather than a minor one. If, in the piece being studied, we find a sharpened leading note then we may be confident that we are in the minor scale represented by the key signature (Example 2).
Capitolo 12 esempio 2
Example in Braille
Example 2 in the key of G minor (Schumann "Faschingsschwank aus Wien op. 26-romanza")

The leading note of a minor key may well, howver, be unaltered if it is part of a descending melody since it is only when it approaches resolution on the tonic that the semitonal relationship to the tonic is valued. In this case we must proceed in our analysis by identifying other instances of the minor key leading note and if they are not sharpened then the key is major. For further confirmation is then necessary to identify the leading note of the major key and check if it actually acts as a leading note resolving on to the tonic of the major key. (Example 3).
Capitolo 12 esempio 3
Example in Braille
Example 3 in the key of A minor (Bach English Suite no. 2)

3) A succession of dominants and tonics.
A succession of dominants and tonics (or vice versa) will give a strong indication of the tonality (Example 4).
Capitolo 12 esempio 4
Example in Braille
Example 4 in the key of A minor (Bach English Suite no. 2)

4) The sharpened 4th degree of the scale.
The sharpening of the 4th degree of the scale (subdominant) is a clear indication as to the tonality. The subdominant is sometimes sharpened to create a kind of false leading note to the dominant (5th degree of the scale). It is usually then very soon returned to its original pitch in order to emphasise that this is simply a passing chromaticism and not a true modulation. In example 5, in B flat major, there is an E natural (sharpened 4th degree of the scale) which resolves on to the dominant (F) of B flat major.
Capitolo 12 esempio 5
Example in Braille
Example 5 in the key of B flat major.

5) Other scales.
The presence of other chromatic alterations can indicate the use of other scales such as the melodic minor, the Neapolitan, harmonic major etc. In example 6, from Schumann, the G flat (flattened 6th degree of the scale) indicates the harmonic major form of B flat major.
Capitolo 12 esempio 6
Example in Braille
Example 6 in B flat major (Schumann op. 26-Finale)

11.2 Modulation

The term modulation indicates the passage, during a piece of music, from one key to another. Modulation is a significant event in a piece because the music now uses a new scale in which the melody and harmony gravitate towards a new tonic.
The most common notes to be changed in a modulation are the 4th and the 7th.
Sharpening the 4th degree of a major scale modulates to the dominant of that scale. For example if, in the scale of A major, the note D is sharpened then the music has modulated to E major.
Flattening the 7th degree of a major scale modulates to the subdominant of that scale. For example if, in the scale of A major, the note G# is flattened then the music has modulated to D major.
We can identify three types of modulation:

  1. modulation to neighbouring, or closely related, keys
  2. modulation to related keys
  3. modulation to distant keys

1) Modulation to neighbouring, or closely related, keys.
We describe a key as closely related if, relative to the original key, there is no more than one note different. Every key has five closely related keys. By way of example let us look at the key of D major which has 2 sharps in its key signature and has the following closely related keys:

the relative minor B minor
with an additional sharp A major
the relative minor of A major F# minor
with one less sharp G major
the relative minor of G major E minor

2) Modulation to related keys
The keys in this second level of relatedness to the original key are defined as having at least one chord in common with it. For example, the key of C major has two chords in common with the key of D major – the chord of E minor (which is the mediant (III) of C major and the supertonic (II) of D major) and the chord of G major (which is the dominant (V) of C major and the subdominant (IV) of D major). Capitolo 12 esempio 6a

3) Modulation to distant keys.
The distant keys are all those that have no chords in common with the original key. For example B flat major is a distant key with respect to D major.
The transition to a new tonality can, in most cases, be recognised at a well-defined point or harmonic sequence in the music. After this transition, the new tonality is almost always confirmed with harmonic progressions characteristic of the new key.

11.3 The techniques of modulation

1) Modulation using a common harmony.
This is a technique of modulation that introduces the new key not in a sudden manner but via a chord that, while it is common to both keys, has different functions in the two keys. For example, to modulate from C major to D major we may employ the chord of G major (which is the dominant (V) of C major and the subdominant (IV) of D major).
Capitolo 12 esempio 7
Example in Braille

2) Chromatic modulation.
In chromatic modulation, one of the notes in the first key changes chromatically (or may be reinterpreted enharmonically) to be part of the new key.
The following example shows a modulation from C major to G major by sharpening the F to F#, the leading note of G major (bar 2). Then, in bar 3, the G is sharpened to G#, the leading note of A minor, the key in which the extract ends.
Capitolo 12 esempio 8
Example in Braille

The techniques of modulation certainly do not end here; in fact, looking at the works of the great composers, it is easy to see that they all diverse and original approaches to modulation.

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