The difference between tied notes and slurred notes in music can cause confusion—which is not surprising, since they are both noted the exact same way! Both slurs and ties are indicated with arc-shaped lines placed either above a grouping of notes (if the notes’ stems are pointing down) or below a grouping of notes (if the stems are pointing up).
However, these curved lines connecting two or more notes function very differently depending on the context. A “tie” is a rhythmic indication, while a slur is a phrasing marking.
Ties connect two or more notes of the same pitch: All of the notes within the tie are sustained smoothly, with their individual rhythmic values combined. In other words, the tied notes function as a single note. (The only exception to this comes if articulation markings, such as accents or staccato markings, also appear within the tie. In this case, the markings call for re-articulation of the individual notes, for example, through bow pressure in string instruments or from tonguing in wind instruments.)
Ties are essential in order to notate pitches sustained across a barline; in other instances, it may be possible to notate a tied rhythm in a different way, but the use of a tie makes it clearer to see where the beat falls.
In the example below, the tie on the C allows the pitch to carry across the barline. On the other hand, the A at the end of the tune technically could be notated with a dotted quarter note, but the tie clearly distinguishes the fourth beat—which makes the music a bit easier to read.
Slurs connect notes of differing pitches. Here, the arched line indicates that the notes should be played legato—smoothly and seamlessly—despite the pitches changing.
In the version of the same tune below, the first two notes, D and E, are now slurred—and therefore, should be smoothly connected together.
Bowed string instruments slur notes by playing them within a single bow stroke, and guitarists slur by playing multiple notes with the left hand without plucking or strumming the strings again with the right hand. Wind and brass instruments, as well as singers, perform all of the notes within the slur in a single breath. (In vocal music, this is known by a different name: a “melisma.”) For piano, the definition is not quite so tangible, but just as with any other instrument, slurs are accomplished by ensuring connectivity from note to note.
In the final example below, notice that it is possible for a tie to be included within a slur. (However, it would not be possible for a slur to be included within a tie, because ties only connect notes of the same pitch!)