Triads
Chords consisting of three notes

Major and minor

A major triad can also be described by its intervals: the interval between the bottom and middle notes is a major third and the interval between the middle and top notes is a minor third.

In Western classical music from 1600 to 1820 and in Western pop, folk and rock music, a major chord is usually played as a triad. Along with the minor triad, the major triad is one of the basic building blocks of tonal music in the Western common practice period and Western pop, folk and rock music. It is considered consonant, stable, or not requiring resolution. In Western music, a minor chord "sounds darker than a major chord", giving off a sense of sadness or somber feeling.

A major
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A
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A unique particularity of the minor chord is that this is the only chord of three notes in which the three notes have one harmonic – hearable and with a not too high row – in common (more or less exactly, depending on the tuning system used). This harmonic, common to the three notes, is situated 2 octaves above the high note of the chord. This is the sixth harmonic of the root of the chord, the fifth of the middle note, and the fourth of the high note:

In the example C, E♭, G, the common harmonic is a G 2 octaves above.

Demonstration:

  • Minor third = 6:5 = 12:10
  • Major third = 5:4 = 15:12
  • So the ratios of minor chord are 10:12:15
  • And the explication of the unique harmonic in common, between the three notes, is verified by : 10 × 6 = 12 × 5 = 15 × 4

Suspended chords

A suspended chord (or sus chord) is a musical chord in which the (major or minor) third is omitted and replaced with a perfect fourth or, less commonly, a major second. The lack of a minor or a major third in the chord creates an open sound, while the dissonance between the fourth and fifth or second and root creates tension. When using popular-music symbols, they are indicated by the symbols "sus4" and "sus2".

The term is borrowed from the contrapuntal technique of suspension, where a note from a previous chord is carried over to the next chord, and then resolved down to the third or tonic, suspending a note from the previous chord. However, in modern usage, the term concerns only the notes played at a given time; in a suspended chord, the added tone does not necessarily resolve and is not necessarily "prepared" (i.e., held over) from the prior chord. As such, in C–F–G, F would resolve to E (or E♭, in the case of C minor), but in rock and popular music, "the term is used to indicate only the harmonic structure, with no implications about what comes before or after," though preparation of the fourth occurs about half the time and traditional resolution of the fourth occurs usually. In modern jazz, a third can be added to the chord voicing, as long as it is above the fourth.

Each suspended chord has two inversions. Suspended second chords are inversions of suspended fourth chords, and vice versa. For example, Gsus2 (G–A–D) is the first inversion of Dsus4 (D–G–A) which is the second inversion of Gsus2 (G–A–D). The sus2 and sus4 chords both have an inversion that creates a quartal chord (A–D–G) with two stacked perfect fourths.

Sevenths on suspended chords are "virtually always minor sevenths", while the 9sus4 chord is similar to an eleventh chord and may be notated as such. For example, C9sus4 (C–F–G–B♭–D) may be notated C11 (C–G–B♭–D–F).

A suspended second
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Augmented and diminished

A diminished triad (also known as the minor flatted fifth) is a triad consisting of two minor thirds above the root. It is a minor triad with a lowered (flattened) fifth. When using chord symbols, it may be indicated by the symbols "dim", "o", "m♭5", or "MI(♭5)". However, in most popular-music chord books, the symbol "dim" and "o" represents a diminished seventh chord (a four-tone chord), which in some modern jazz books and music theory books is represented by the "dim7" or "o7" symbols.

In major scales, a diminished triad occurs only on the seventh scale degree. For instance, in the key of C, this is a B diminished triad (B, D, F). Since the triad is built on the seventh scale degree, it is also called the leading-tone triad. This chord has a dominant function. Unlike the dominant triad or dominant seventh, the leading-tone triad functions as a prolongational chord rather than a structural chord since the strong root motion by fifth is absent.

On the other hand, in natural minor scales, the diminished triad occurs on the second scale degree; in the key of C minor, this is the D diminished triad (D, F, A♭). This triad is consequently called the supertonic diminished triad. Like the supertonic triad found in a major key, the supertonic diminished triad has a predominant function, almost always resolving to a dominant functioning chord.

If the music is in a minor key, diminished triads can also be found on the raised seventh note, ♯viio. This is because the ascending melodic minor scale has a raised sixth and seventh degree. For example, the chord progression ♯viio–i is common.

The leading-tone diminished triad and supertonic diminished triad are usually found in first inversion (viio6 and iio6, respectively) since the spelling of the chord forms a diminished fifth with the bass. This differs from the fully diminished seventh chord, which commonly occurs in root position. In both cases, the bass resolves up and the upper voices move downwards in contrary motion.

A augmented
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The term augmented triad arises from an augmented triad being considered a major chord whose top note (fifth) is raised. When using popular-music symbols, it is indicated by the symbol "+" or "aug". For example, the augmented triad built on C, written as C+, has pitches C–E–G♯:

Whereas a major triad, such as C–E–G, contains a major third (C–E) and a minor third (E–G), with the interval of the fifth (C–G) being perfect, the augmented triad has an augmented fifth, becoming C–E–G♯. In other words, the top note is raised a semitone.

The augmented triad on the V may be used as a substitute dominant, and may also be considered as ♭III+. The example below shows ♭III+ as a substitute dominant in a ii-V-I turnaround in C major.

Though rare, the augmented chord occurs in rock music, "almost always as a linear embellishment linking an opening tonic chord with the next chord," for example John Lennon's "(Just Like) Starting Over" and The Beatles' "All My Loving". Thus, with an opening tonic chord, an augmented chord results from ascending or descending movement between the fifth and sixth degrees, such as in the chord progression I – I+ – vi. This progression forms the verse for Oasis's 2005 single "Let There Be Love" (I – I+ – vi – IV)

Synthetic triads

A synthetic chord is a made-up or non-traditional (synthetic) chord (collection of pitches) which cannot be analyzed in terms of traditional harmonic structures, such as the triad or seventh chord.

This title is applied to a group of notes, usually a scale-like succession of pitches, with a fixed progression of tones and semitones. This scale can obviously be transposed to any pitch, and depending on its intervallic makeup, will have a fixed number of possible transpositions. Furthermore, the sintetakkord can be used either vertically or horizontally; Roslavets' music is not concerned with the order of the pitches, but rather with the whole 'field' thus created, so that the system is less oriented toward themes and more toward harmonic fields.

— Sitsky (1994)

A Mb5
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