At its simplest, a song is a musical composition that combines melody and lyrics. A song may also contain harmony and rhythm, or beats. It typically has a verse and chorus, and it often repeats the same sections. It can also have a refrain. The words of a song are called lyrics, and they can tell a story or evoke emotion.
A song can vary in complexity, and it can be a folk or popular song, an art song or a classical piece of music. Despite their differences, all songs have some common features.
One important aspect is ornamentation, which refers to the complex variations of a perceived underlying musical structure. Examples include changes in melodic contour, harmonic progression, rhythm, motivic development and accent. A song with a high value for this variable has a lot of melody variation and complexity. Another important variable is the number of different pitch classes, which measures how many pitches sound equally equivalent in a range of octaves. For example, a song that uses all of the notes in the scale of C will have a higher score than one that uses only the pitches in the key of A. A third variable is the proportion of a song’s intervals that are based on steps. A song that uses many leaps between adjacent notes will have a low score.
These variables can help us distinguish between the four song types (dance, healing, love, and lullabies) as well as the subtypes within each type. For example, dance songs differ from lullabies in their tempo and accent, and dance songs tend to have more melodic variation than healing songs.