Secondary dominant
The dominant of a degree other than the tonic.
What it means
A secondary dominant is a dominant sonority that relates not to the tonic but to a different degree of the key. It treats this degree, for a moment, like a tonic and places its own dominant before it. The term Nebendominante designates the same thing.
In the notation
Secondary dominants are recognizable by notes foreign to the scale, mostly by an accidental that produces a leading tone to the target degree. In C major, the dominant of D minor needs a C-sharp, the dominant of E minor a D-sharp, the dominant of the dominant an F-sharp. In keys with many accidentals, double sharps or natural signs may become necessary for this. In function symbols, secondary dominants are placed in brackets or given an arrow pointing to the following sonority.
Musical use
Secondary dominants colour a passage without leaving the key. They sharpen the goal direction of individual degrees, create additional leading tones, and make harmonic progressions more urgent. In cadences, the dominant of the dominant, the double dominant, is especially frequent: it stands before the cadential six-four chord or directly before the dominant and reinforces its entry. If several secondary dominants follow one another, a chain of dominants in falling fifths arises.
The secondary dominant is to be distinguished from three related phenomena. The double dominant is its most frequent special case, namely the secondary dominant to the dominant. Modulation permanently relocates the tonal centre and confirms it through a cadence; the secondary dominant, by contrast, colours a degree only temporarily, after which the main key continues to apply. And the altered chord changes an existing chord tone, while the secondary dominant brings a new leading tone to a different degree.
Other names
Nebendominante is mostly used synonymously. Some textbooks distinguish: it is called Zwischendominante when it is the dominant of a degree other than the tonic and resolves directly into that degree; it is called Nebendominante as a sonority in its own right, even if the resolution fails to occur. Both differ from modulation in that the home key remains in force.
Performance practice
Look for the note foreign to the scale and lead it as a leading tone to its goal; intonate it close. Shape the target degree as a brief point of rest, without losing the main key from your ear. And mark secondary dominants when analysing — they show where the music builds up pressure.