From Teflpedia

A circumstance (/ˈsɜ:.kəm.stəns/) is a semantic property of an events and states.

In terms of events it expresses:

  1. The place where the event occurs (question word - where?)
  2. The manner in which the event occurs - how?
  3. The time at which the event occurs. when?
  4. The duration of the event; how long?
  5. The number of occurrences of the event - how many times?
  6. The frequency that the event occurs - how often?
  7. The reason why the event occurs; why?
  8. The degree to which something occurs - how much?
  9. The result of the event. (no question word in English).

In English, circumstances are expressed using adverbials. There are also specific circumstantial adverbs.