To oblige a person or entity to do something is to require or force them to do it, either because of a law or rule, or because it is necessary. To simply oblige someone is to do them a favor.

// The law obliges the government to release certain documents to the public.

// When my friend said he needed someone to taste test his new recipe for the cooking competition, I was happy to oblige.

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“I was irked 30 years ago when our neighbor said she intended to install a free-standing fence between our driveways. … It seemed unneighborly to humans and wildlife alike. We were a family who spent more time outdoors than in, always nearby when our neighbor pulled into her driveway. Once the fence was up, she was no longer obliged to speak to us.” — Margaret Renkl, New York Times, 2 June 2025

If you are obliged by a rule or law you are metaphorically bound by it—that is, you are required to obey it. The idea of binding links the word to its Latin source, ligāre, meaning “to fasten, bind.” But in other common uses, the idea of binding is somewhat masked: it is applied when someone is bound by a debt for some favor or service, as in “We’re much obliged to you for the help,” but in the phrase “happy to oblige” it simply expresses a willingness to do someone a favor, as in “They needed a ride and we were happy to oblige.”