Barline
A vertical line separating bars; the accented downbeat lies directly after it.
What it means
The barline is the vertical line separating two bars from each other. Immediately after it the new bar begins, and with it the accented downbeat. The line itself is no sign for an accent, no rest, and no caesura — it organizes the notation, nothing more. That the downbeat is strong follows from the time signature, not from the line.
Alongside the simple barline there are further forms. The double bar, two thin lines, marks the end of a section or stands before a change of time signature or key signature. The final barline, of one thin and one thick line, ends the piece. If two dots are added, it becomes a repeat sign. The dashed barline organizes within a bar without dividing it and is used with irregular time signatures to show the groups.
In the notation
The barline reaches, in a single staff, from the lowest to the highest line. In scores it can be drawn through several staves, to connect instrument groups belonging together; with vocal parts it often remains limited to the single staff. Accidentals apply only within one bar and lose their validity with the next barline.
Musical use
The consistent use of barlines becomes established in the sixteenth and seventeenth centuries. In older music they are absent, and modern editions of early music sometimes place them only between the staves, so as not to obscure the freer metric order. In twentieth-century music the barline is at times given up altogether or set irregularly.
The double bar separates larger sections.
Performance practice
Read across the barline: phrases rarely end where it stands, and an automatic accent after every line chops up the line. Conversely, take care that the bar order nonetheless remains perceptible. Remember the rule for accidentals — with the barline, the key signature begins to apply again. And use double bars, when practising, as points of orientation for the form.