A tempo
Return to the original tempo after a change.
What it means
A tempo is Italian and means literally “in time”. The instruction cancels a preceding tempo change: after a ritardando, an accelerando or a free passage, the music returns to the tempo that held before the change. A tempo thus names no new tempo but points back to one already known. In this it differs from markings such as Allegro or ♩ = 120, which set a tempo independently.
A tempo is also to be distinguished from tempo primo (also tempo I): tempo primo expressly calls for the opening tempo of the piece, even if quite a different tempo was introduced in between. A tempo, by contrast, means only the tempo that held immediately before — which may, but need not, be the opening tempo.
In the notation
The marking stands above the staff, usually in italics, and holds from the note above which it appears. As a rule it follows shortly after a tempo change, often immediately after the end of a ritardando led by a dashed line. In piano and chamber-music editions it appears in every part involved, so that all players see the common re-entry.
Some editions supplement a tempo with a metronome figure in brackets. These figures often come from the editors and not from the composer; they are to be read as a guide and can differ from edition to edition.
Musical use
A tempo almost always marks a formal seam: the end of a transition, the return of a main theme, the fresh start after a cadenza. The effect lies in the contrast — the clearer the preceding holding-back, the more strongly the return acts as a breath of relief or a new run-up. In the music of the Viennese Classicism a tempo usually stands terse and matter-of-fact; in Romanticism it becomes part of a larger dramaturgy of tempo, with frequent alternation between stretching and restoring.
Performance practice
Take up the old tempo again at once and fully, not gradually — otherwise the effect is blurred. It helps to count the basic tempo inwardly while you slow down, so that at the re-entry you have a firm point of reference. In an ensemble it is worth rehearsing the spot deliberately: whoever is back in tempo first gives the others the impulse. See that the return does not become louder merely because it becomes faster — here tempo and dynamics are independent of each other.