A slur is a symbol in Western musical notation indicating that the notes it embraces are to be played without separation, i.e. with legato articulation. A slur is denoted with a curved line generally placed over the notes if the stems point downward, and under them if the stems point upwards:
The slur is not to be confused with two other similar musical symbols. The tie is a curved line that links two notes of the same pitch to show that their durations are to be added together. The phrase mark is a curved line that extends over a passage which is visually indistinguishable from the slur, and indicates that the passage is to be interpreted as a single phrase.
When two instruments written on the same staff both have slurred phrases with the same note values (e.g., clarinets playing in thirds) it is customary to have two sets of slurs, though in some scores just one set is used and it is understood to apply to both of the instruments.
- For bowed string instruments, the notes should be played in one bow.
- For guitars, the notes should be played without plucking the individual strings (hammer-ons and pull-offs).
- For wind instruments, the notes should be played without rearticulating each note (tonguing), except in trombone.
- For vocal music, slurs are usually used to mark notes which are sung to a single syllable (melisma).
A slur can be extended over many notes, sometimes encompassing several bars. In extreme cases, composers are known to write slurs which are near-impossible to achieve; in that case the composer wishes to emphasise that the notes should be performed with as much legato as possible.