Music, like any other area of study, has a very specialized vocabulary. In order to speak intelligently with other musicians, you need to know and understand a wide variety of these terms. Unfortunately, some of these terms can be quite difficult for a musician to understand at first. Theme and motif are two similar musical terms that novices often get confused.
A musical theme is a specific musical figure that is the basis of an entire composition. Musical themes can be either melodic or rhythmic in nature. Themes will repeat several times throughout a piece of music. The theme of a piece of music can be slowed down, sped up, transposed into a different key or otherwise altered. The theme should, however, remain recognizable. In the vast majority of cases, a theme is several measures long.
A motif is a tune, melodic or harmonic in nature, or a rhythm that helps to unify or characterize a composition. In general, motifs are fairly short -- a few measures at most -- but there is no technical limit to the length of a motif. Motifs are often repeated several times throughout a piece of music, and they should be easy for the astute listener to pick up. Some motifs, known as leitmotifs, can also identify a certain character, place or feeling. This use of motif is especially prevalent in opera.
Theme Versus Motif
A theme is a larger, more important unit than a motif. Even if the motif were to contain more measures than the theme -- an extremely unlikely occurrence -- the theme would still be more important to the overall composition of a piece of music. In addition, a motif can actually be placed within the musical theme of a composition, either from the first time the theme is sounded or added later as an alteration of the theme. Finally, motifs and themes can be altered. Motifs tend to lend themselves to a greater degree of alteration than themes.
Beethoven's "Symphony No. 9" is built around an extremely well-known theme. The first 16 measures of this composition make up the theme, which is then repeated and slightly changed throughout the song. Another Beethoven piece, "Symphony No. 5," uses one of the most recognizable motifs in the history of music. The dire-sounding first four notes of the first movement of this symphony are repeated and altered several times throughout the piece of music, serving to unify the sections. This motif is only two measures long, much shorter than the theme in "Symphony No. 9."
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