Mordent and turn: signs, variants, and performance

Definition

The mordent and the turn (gruppetto) are short ornaments that circle around the main note.

The mordent is a single, very rapid oscillation: main note, neighbor note, main note.
The turn is a figure of four or five notes that wraps around the main note, touching the upper and the lower neighbor.

Type	Sign	Performance on C
Upper mordent (in German Pralltriller)	short wavy line	C–D–C
Lower mordent	wavy line crossed by a vertical stroke	C–B–C

It is performed on the beat, with the first two notes very fast and the last taking the rest of the value.
A small accidental above or below the sign modifies the neighbor note.
In the table of ornaments that Bach wrote for his son Wilhelm Friedemann, the true “mordent” is the lower one; the upper one is meant as a very short trill. In modern Italian terminology both names are used, specifying upper or lower.
In the Baroque, the upper mordent that follows a tied higher note behaves like a small trill starting from above.

The sign is a sideways S. Its position changes the performance:

Above the note: performed immediately, on the beat: upper note, main note, lower note, main note (D–C–B–C).
Between two notes (shifted to the right): first the main note is played, then the turn at the end of its value: C–D–C–B–C and then the next note. This is the most common form in Classical and Romantic music.
Inverted turn (sign turned upside down or with a vertical stroke): starts from below, B–C–D–C.
Accidentals above the sign refer to the upper note, those below to the lower note. In C major, a turn on A with a sharp below the sign requires G#.

The turn between two notes is placed toward the end of the value of the first note: it should not be anticipated.
The rhythm of the turn adapts to the tempo: in an Adagio it can be almost sung, in an Allegro it is as quick as an extended mordent.
On the lower note of the turn a half step is often used even when the scale would give a whole step, to give the main note a leading-tone function (particularly on the fifth degree).

Bach, Keyboard Suites and Partitas: mordents on almost every long note, especially at the beginning of dances.
Bellini, “Casta diva” (Norma): the vocal line is ornamented with turns that make the melody fluid and singable.
Chopin, Nocturnes: turns and flourishes derived from Italian bel canto.
Wagner: the turn is a signature of his melodic writing, so much so that people speak of the “Wagnerian turn”.
In R&B and soul singing, the “turn” on the final note (above, main, below, main) is a vocal turn.

The mordent gives bite to the attack of a note without changing its duration: excellent in dance themes.
The turn connects two distant notes, making the passage smooth and vocal.
In a very simple melody, a single turn at the climactic point can be enough to make it expressive.
In MIDI, program mordents and turns with notes of 30–60 ms, slightly below the velocity of the main note.

Write out in full the performances of the upper mordent, lower mordent, turn above the note, and turn between two notes on G in C major.
Add three turns to a slow eight-bar melody, at different points of the phrase, and choose the most effective one.
Sing a turn on the final note of a pop phrase, then transcribe it.

Ornaments; Trill; Acciaccatura and appoggiatura; Passing tones and neighbor tones; Ad-libs and vocal runs; Melodic writing and contour.