Sforzando
A single note or chord suddenly accented, independent of the basic volume.
What it means
Sforzando comes from sforzare, “to execute with force,” and calls for a single note or chord to be suddenly brought out. Abbreviated it appears as sf or sfz. After the accented note the previous dynamic applies again — the marking does not change the basic volume.
Decisive is that the sforzando relates to its respective context. In a pianissimo section, an sf is distinctly softer than in a forte section; what is meant is a contrast to the surroundings, not an absolute value. Playing a sforzando in a soft passage as an outburst misjudges the marking.
Compared with rinforzando, which reinforces a short group, the sforzando is at a single point. It differs from the accent sign by degree: the sforzando counts as the stronger emphasis.
In the notation
The abbreviation stands below the staff, for vocal parts above the text, directly at the note concerned. Related forms are sfp, which calls for a sharp attack with an immediately following piano, and fz (forzando). With chords, the marking applies to all the notes of the sonority.
Musical use
The sforzando sets accents against the metric order: on unaccented beats, in syncopations, at points where the listener expects no emphasis. It is thus one of the most effective means of disturbing a regular metre. In the Viennese Classical period it is extraordinarily frequent; there it often stands in series on light beats and shifts the accent across several bars.
Other names
Sforzato has the same meaning and is likewise abbreviated sf or sfz. Both forms come from sforzare, to force, and designate a sudden, strong accent on a single note or chord.
Performance practice
Relate the strength to the surroundings: an sf in piano stays soft. Place the emphasis in the attack and pull back immediately afterward, instead of continuing to play louder. Take care that the note does not become hard — the emphasis should arise from a definite beginning, not from pressure. And check whether the spot is metrically accented: precisely on light beats the sign works most strongly.