When we talk about responsibility, we often use the phrase "is one's duty to". However, there are many other synonyms that can help us convey the same message. These include "is incumbent upon", "is obliged to", "should", "must", "needs to", "has an obligation to" and "ought to". Depending on the context, one synonym may be more appropriate than another. For example, "is incumbent upon" may be more suitable in a formal or legal setting, while "should" may be more appropriate in a casual conversation. Using synonyms can help us vary our language and avoid repeating the same phrases, making our communication more effective.