A slur, sometimes called a phrase mark, is a curved line used in musical notation which indicates that the notes are to be played smoothly together. String players will typically play the notes in one stroke of the bow, wind players or singers will take the notes in one breath.
Slurs are also used in vocal music to indicate that one syllable is to be sung across several notes, called a “melisma“.
When writing music, it is important that the extent of a phrase be immediately clear to the musicians.
When a phrase ends with a tied note, it’s perhaps natural to want to attach the phrase mark to the start of the tied series, but, except in one specific case we will cover in a moment, this is actually incorrect.
One slur should completely cover the entire phrase, with the end of the slur attached to the final tied note in the series. The following is correct:
Here is another example:
A series of tied notes across several bars is the one exception to the above rule.
“When a final pitch is extended by a series of tied notes, jt is acceptable (and a convention) to end the slur with the first whole-bar duration (a); alternatively, in cramped conditions, with the first tied note (b):”