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Music theory book


10.1 Defining Chords

A chord is a set of three or more notes which are sounded at the same time or in melodic succession. The study of the classification and relationship between chords is known as Harmony.
If only two notes are sounded together (diad) they do not form a chord because it is not possible to define them within the tonal system.
In printed musical notation chords of less than a semibreve in length are attached to a stem. The direction of the stem is governed by the note in the chord that is least far from the third (middle) line of the staff (Ex. 1).
In the case of equal distance the stem by convention goes downwards (Ex. 2).
If two notes in a chord are a 2nd apart then one will be on the left and one on the right of the stem (Ex. 3).
esempio 1

10.2 The triad

A chord formed by three notes made up of two intervals of a 3rd superimposed (with respect to the lowest note, an interval of a 3rd and a 5th) is the simplest element in harmony: the triad.
The lowest note of such chords is called the root and it determines the name of that chord.
Example: the triad of G major:
Triade di sol maggiore composta dalle note sol di re

Because of the different types of 3rd (major or minor) and 5th (perfect, diminished or augmented) four types of triad are possible:

  1. Major triad = Major 3rd + Minor 3rd (or, relative to the root, a major 3rd and a perfect 5th)
  2. Minor triad = Minor 3rd + Major 3rd (or, relative to the root, a minor 3rd and a perfect 5th)
  3. Diminished triad = Minor 3rd + Minor 3rd (or, relative to the root, a minor 3rd and a diminished 5th)
  4. Augmented = Major 3rd + Major 3rd (or, relative to the root, a major 3rd and an augmented 5th)

serie di triadi maggiore, minore, diminuita, eccedente
Braille example

The notes of a chord may be arranged in the following forms:

  1. Triad in root position (3rd + 5th)
  2. Triad in first inversion (3rd + 6th)
  3. Triad in second inversion (4th + 6th)

triadi allo stato fondamentale, in primo e in secondo rivolto
Braille example

10.3 Primary triads

The triads constructed on the first (tonic), fourth (subdominant) and fifth (dominant) degrees of the scale are known as the primary triads and together they include all the notes of the scale:
gli accordi principali
Braille example

The triads constructed on other degrees of the scale - sixth, second and seventh - are known as the secondary triads because they are simply derivatives of the primary triads. Each of them, in fact, has two notes in common with the relative primary triad, two notes that define clearly the harmonic group to which they belong:
accordi principali e secondari

The triad built on the third degree of the scale is “hybrid” insofar as it contains elements of both the tonic and dominant primary triads. It contains an E, characteristic of the tonic triad and it contains a B, characteristic of the dominant triad.
la sensibile e la caratteristica

10.4 Four-note chords (tetrads)

Adding a fourth note to a triad at an interval of a third produces a tetrad or seventh chord.
This can have four inversions:
Le quadriadi rivoltate

A seventh chord much used is that built on the dominant (fifth degree of the scale). Such a seventh chord contains notes that are characteristic of the key (dominant and subdominant) and has a natural tendency to resolve onto the tonic chord.
The classification of the seventh chords depends upon the type of 7th interval it contains and the type of triad from which it is formed.
Here are some examples of seventh chords:
Braille example

By convention, when a seventh chord is formed from a major triad this part of the label is often left out. Therefore a chord with a minor 7th on a major triad will be referred to as a dominant seventh. If it formed from a minor triad it will be called a minor seventh.
A seventh chord formed from a major 7th on a major triad will be referred to as a major seventh.
Sometimes the chord will be referred to only in terms of the type of triad on which it is built without reference to the type of 7th interval it contains.
The chord formed from the diminished 7th interval and a diminished triad is usually referred to as a diminished seventh chord.
Here are some examples:
Accordi di settima
Braille example

10.5 5-note chords

Adding a fifth note to a seventh chord produces a chord of a ninth. The classification is similar to that of the seventh chords, that is one names the type of ninth, then the type of seventh and then the type of triad.
Accordi di 5 suoni
Braille example

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