In order to stress or emphasise a certain note or chord, besides the marks of expression decrescendo and sf, chords of 2, 3, and 4 notes can be inserted into the melodic progression by the instruments of the string quartet, each playing a single note; short notes in the wood-wind may also be used as well as a chain of three or four grace notes, in the form of a scale, either in strings or wood-wind. These unstressed notes (anacrusis), generally written very small, form a kind of upward glide, the downward direction being less common. As a rule they are connected to the main note by a slur. In the strings they should not lead up to chords of three or four notes, as this would be awkward for the bow.