In music notation, a note value indicates the relative duration of a note, using the color or shape of the note head, the presence or absence of a stem, and the presence or absence of flags/beams/hooks/tails.
A rest indicates a silence of an equivalent duration.
|Note||Rest||American name||British name||Value||Dotted Value||Double Dotted Value||Tripled Dotted Value|
|double whole note||breve||8||12||14||15|
|whole note||semibreve||4||6||7||15/2 or 7 1/2|
|half note||minim||2||3||7/2 or 3 1/2||15/4 or 3 3/4|
|or||quarter note||crotchet||1||3/2 or 1 1/2||7/4 or 1 3/4||15/8 or 1 7/8|
|hundred twenty-eighth note||Quasihemidemisemiquaver Semihemidemisemiquaver||1/32||3/64||7/128||15/256|
The breve appears in several different versions, as shown at right.
Sometimes the longa is used to indicate a very long note of indefinite duration, as at the end of a piece.
When a stem is present, it can go either up (from the right side of the note head) or down (from the left side, except in the case of the longa). In most cases, the stem goes down if the notehead is on the center line or above, and up otherwise. Any flags always go to the right of the stem.
When two or more notes which would normally have flags (eighth notes or shorter) appear successively, the flags may be replaced by beams, as shown at right. Notes are typically beamed only if they appear in the same beat within the bar.
A note value may be augmented by adding a dot after it. This dot adds the next lower note value, making it one and a half times its original duration. A number of dots (n) lengthen the note value by its value, so two dots add two lower note values, making a total of one and three quarters times its original duration. The rare three dots make it one and seven eighths the duration, and so on.
Gregorian chant 
Although note heads of various shapes, and notes with and without stems appear in early Gregorian chant manuscripts, many scholars agree that these symbols do not indicate different durations, although the dot is used for augmentation. See neume.
In the 13th century, chant was sometimes performed according to rhythmic modes, roughly equivalent to meters; however, the note shapes still did not indicate duration in the same way as modern note values.
Mensural notation 
Around 1250, Franco of Cologne invented different symbols for different durations, although the relation between different note values could vary; three was the most common ratio. Philippe de Vitry's treatise Ars nova (1320) described a system in which the ratios of different note values could be 2:1 or 3:1, with a system of mensural time signatures to distinguish between them.
This black mensural notation gave way to white mensural notation around 1450, in which all note values were written with white (outline) noteheads. In white notation the use of triplets was indicated by coloration, i.e. filling in the noteheads to make them black (or sometimes red). Both black and white notation periodically made use of ligatures, a holdover from the clivis and porrectus neumes used in chant.
Around 1600 the modern notational system was generally adopted, along with barlines and the practice of writing multipart music in scores rather than only individual parts. In the 17th century, however, old usages came up occasionally.
Origins of the names 
The British names go back at least to English renaissance music, and the terms of Latin origin had international currency at that time. Obviously, longa means 'long', and the rest mostly indicate relative shortness. Breve is from Latin brevis, 'short', minim is from minimus, 'very small', and quaver refers to the quivering effect of very fast notes. The elements semi-, demi- and hemi- mean 'half' in Latin, French and Greek respectively, while quasi- means 'almost'. The chain semantic shift whereby notes which were originally perceived as short came progressively to be long notes is interesting both linguistically and musically. However, the crotchet is named after the shape of the note, from the Old French for a 'little hook', and it is possible to argue that the same is true of the minim, since the word is also used in palaeography to mean a vertical stroke in mediaeval handwriting.
|Wikisource has the text of a 1905 New International Encyclopedia article about Note value.|