Secondary dominant (also applied dominant) is an analytical label for a specific harmonic device, prevalent in the tonal idiom of Western music beginning in the common practice period. It refers to a dominant-like function of a chromatically altered chord built on a scale degree other than the 5th of the prevailing key, with V7/V, the dominant of the dominant, "being the most frequently encountered".[1] The chord to which a secondary dominant progresses can be thought of as a briefly tonicized chord or pitch (tonicizations longer than a phrase are modulations). The secondary dominant terminology is still usually applied even if the chord resolution is nonfunctional (for example if V/ii is not followed by ii).[2]
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The normal diatonic major scale defines six (in one view, seven) basic chords, designated with Roman numerals in ascending order. For instance, in the key of C major, the six basic chords are these:
Of these chords, V (G major) is said to be the dominant of C major (the dominant of any key is the one whose root is a fifth higher). However, each of the chords from ii through vi also has its own dominant. For example, vi (A minor) has E major (Dominant (music)#Triads) as its dominant. These extra dominant chords are not part of the key of C major as such because they include notes that are not part of the C major scale. Instead, they are the secondary dominants.
Below is an illustration of the secondary dominant chords for C major. Each chord is accompanied by its standard number in harmonic notation. In this notation, a secondary dominant is usually labeled with the formula "V of ..."; thus "V of ii" stands for the dominant of the ii chord, "V of iii" for the dominant of iii, and so on. A shorter notation, used below, is "V/ii", "V/iii", etc. The secondary dominants are connected with lines to their corresponding tonic chords.
Note that of the above, V/IV is the same as I. However, as will become clear shortly, they are not always identical.
Like most chords, secondary dominants can be classified by whether they contain certain additional notes outside the basic triad; for details, see Figured bass. A dominant seventh chord (notation: V7) is one that contains the note that is a minor seventh above the root, and a dominant ninth chord (notation: V9) contains the note a ninth above the root. For instance, V7/IV, although it is a C chord, is distinct from regular C major because it also contains the note B flat, which is a minor seventh above the root of C, and not part of the C major scale.
To illustrate, here are the secondary dominants of C major, given as dominant seventh chords. They are shown leading into their respective tonics, as given in the second inversion.
Chromatic mediants, for example vi is also a secondary dominant of ii (V/ii) and III is V/vi, are distinguished from secondary dominants with context and analysis revealing the distinction.[3]
When used in music, a secondary dominant is very often (though not inevitably) directly followed by the chord of which it is the dominant. Thus V/ii is normally followed by ii, V/vi by vi, and so on. This is similar to the general pattern of music wherein the simple chord V is often followed by I. The tonic is said to "resolve" the slight dissonance created by the dominant. Indeed, the sequence V/X + X, where X is some basic chord, is thought of by some musicians as a tiny modulation, acting as a miniature dominant-tonic sequence in the key of X.
The concept of the secondary dominant was not widely recognized in writings on music theory prior to the 20th century. Before this time, in music of Bach, Mozart, Beethoven, and Brahms, a secondary dominant, along with its chord of resolution, was considered to be a modulation. Because the effect of modulation was so short, and did not sound like a real arrival of a new key, the two chords had a special name--"transient modulation"--that is, a modulation in which the new key is not established. Since this was a rather self-contradictory description, theorists in the early 1900s, such as Hugo Riemann (who used the term "Zwischendominante" - "dominant inbetween"), searched for a better description of the phenomenon. One method of signifying these chords at the time (used by both Riemann and Ernst Kurth) was by placing the chord symbol in parentheses, thereby indicating that the chord functions only in relation to the chord immediately following it - for example, (VII) V.
In the English-speaking world, the analysis "V7 of IV" was first used by Walter Piston in 1939, in a monograph entitled "Principles of Harmonic Analysis." (Notably, Piston's analytical symbol always used the word "of"--e.g. "V7 of IV" rather than the virgule "V7/IV.) In his 1941 "Harmony" Piston used the term "secondary dominant" for the first time.
In the Fifth edition of "Harmony" by Walter Piston and Mark DeVoto,[5] a passage from the last movement of Mozart's Piano Sonata K. 283 in G major serves as one illustration of secondary dominants. Below, the harmony alone is first given, labeled both for the literal names of the chords and for their chord number in the key of G major.
It can be seen that this passage has three secondary dominants, each one followed (as expected) by the chord of which it is the dominant. The final four bars form a back-cycle, ending in a standard dominant-tonic cadence, which concludes the phrase. The lines drawn below the diagram show each instance in which a dominant is followed by its corresponding tonic.
The harmony is distributed more subtly between the notes, and goes faster, in Mozart's original:
The secondary dominants here create a rapidly descending chromatic harmony, an effective lead-up to the tonic cadence at the end of the phrase. There are many similar passages in Mozart's music.
In jazz harmony, a secondary dominant is any Dominant chord (major-minor 7th chord) which occurs on a weak beat and resolves downward by a perfect 5th. Thus, a chord is a secondary dominant when it is functioning as the dominant of some harmonic element other than the key's tonic, and promptly resolves to that element. This is slightly different from the traditional use of the term, where a secondary dominant does not have to be a 7th chord, occur on a weak beat, or resolve downward. If a non-diatonic dominant chord is used on a strong beat, it is considered an extended dominant. If it doesn't resolve downward, it may be a borrowed chord.
Secondary dominants are used in jazz harmony in the Bebop blues and other blues progression variations, as are sub V and turnarounds.[6]
Examples include II7 (V7/V) in Bob Dylan's "Don't Think Twice, It's All Right" and III7 (V7/vi) in Betty Everett's "The Shoop Shoop Song (It's in His Kiss)".[7]
An extended dominant is a non-diatonic secondary dominant seventh chord that resolves downwards to another dominant chord. A series of extended dominant chords continues to resolve downwards by perfect fifths until they reach the tonic chord.
Typically used in jazz, extended dominants have been used in other contexts as well.
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