In Western classical music, obbligato (Italian pronunciation: [obbliˈɡaːto], also spelled obligato[1]) usually describes a musical line that is in some way indispensable in performance. Its opposite is the marking ad libitum. It can also be used, more specifically, to indicate that a passage of music was to be played exactly as written, or only by the specified instrument, without changes or omissions. The word is borrowed from Italian (an adjective meaning mandatory; from Latin obligatus p.p. of obligare, to oblige); the spelling obligato is not acceptable in British English,[2] but it is often used as an alternative spelling in the US.[3] The word can stand on its own, in English, as a noun, or appear as a modifier in a noun phrase (e.g. organ obbligato).
The term has also come to refer to a countermelody.[4]
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