Overview
A grace note is a kind of music notation denoting several kinds of musical ornaments. It is usually printed smaller to indicate that it is melodically and harmonically nonessential. When occurring by itself, a single grace note indicates either an acciaccatura when notated with an oblique stroke through the stem, or an appoggiatura when notated without. When they occur in groups, grace notes can be interpreted to indicate any of several different classes of ornamentation, depending on interpretation. For percussion, such as drums, a related concept are ghost notes — supportive snare-hits at a lower volume.
Notation
In notation, a grace note is distinguished from a standard note by print size. A grace note is indicated by printing a note much smaller than an ordinary note, sometimes with a slash through the note stem (if two or more grace notes, there might be a slash through the note stem of the first note but not the subsequent grace notes). The presence or absence of a slash through a note stem is often interpreted to indicate the intention of an acciaccatura or an appoggiatura, respectively.
The works of some composers, especially Frédéric Chopin, may contain long series of notes printed in the small type reserved for grace notes simply to show that the amount of time to be taken up by those notes as a whole unit is a subjective matter to be decided by the performer. Such a group of small printed notes may or may not have an accompanying principal note, and so may or may not be considered as grace notes in analysis.
Function
A grace note represents an ornament, and distinguishing whether a given singular grace note is to be played as an appoggiatura or acciaccatura in the performance practice of a given historical period (or in the practice of a given composer) is usually the subject of lively debate. This is because we must rely on literary, interpretative accounts of performance practice in those days before such time as audio recording was implemented, and even then, only a composer's personal or sanctioned recording could directly document usage.
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