Certainty of occurrence:
* In-: This prefix often implies something is unavoidable or certain to happen, as in "inevitable" or "invariable."
* Un-: Used with words like "unquestionable" or "unavoidable" to indicate certainty or lack of doubt.
* Ir-: This prefix implies an impossibility of changing or altering something, as in "irrevocable" or "irrefutable."
Certainty of knowledge:
* De-: This prefix can emphasize certainty or conviction, as in "definite" or "decisive."
* Con-: Used with words like "confident" or "convinced" to express certainty or strong belief.
* As-: This prefix emphasizes certainty or reliability, as in "assured" or "assuredly."
The best prefix to use will depend on the specific word and the desired nuance of meaning.