Obbligato is traditionally a term for a part of a piece of music that is essential to the composition, and must be played as part of the entire piece. Other pieces of classical music are sometimes marked with the phrase ad libidum, meaning they are not essential to the larger piece of music. The use of this musical term has become somewhat obsolete over time, but is still familiar to music experts who read classical pieces of music in which this marking is used.
Music experts who understand the use of the term obbligato in the time period when it was most used, sometimes explain the term with a synonym such as “indispensable.” Obbligato parts of music were seen as integral to their musical surroundings. They were also often seen as independent from a larger work. In some cases, they added more specific meaning related to the transition between two parts of music. Some obbligato parts were seen as “bridges” or other transitional devices in a piece of music with a changing dynamic.
Depending on context, obbligato parts of a musical composition may be seen as pieces that are essential, but which may be subordinate to another part of the larger piece. Multiple obbligato portions of a piece of sheet music may tie into a larger theme, yet stand on their own in some senses. Music students can look at various pieces of classical music including cantatas, arias, and other compositions of the eighteenth century for examples of this phenomenon in music. Composers like Bach, Mozart, and Beethoven, who were among the greatest and most popular musicians of their time, used this marking in certain parts of their musical compositions.
In modern day music, obbligato is not commonly used. Those who are familiar with the use of this term will generally explain that in modern music, there is no concrete idea of which parts of a piece are more important than others or need to be included in a composition. In general, everything that is written in a modern piece is considered essential, which makes sense to the modern composer and the modern listener; performers generally had more leeway for improvisation in earlier times. Obbligato and some other understandings about music in the classical era have ceased to be relevant in the present era, but these markings can of great interest to music historians seeking an understanding of how these works were originally perceived and performed.