The term "ex-postulate" is not commonly used in everyday language, and it does not have widely recognized antonyms. Ex-postulate refers to a statement or proposition that is made after something has been proven or established. Some possible antonyms could include "hypothesis," "speculation," or "conjecture," which suggest a lack of proof or evidence. Other antonyms could include terms that describe statements made before an event has occurred or before evidence has been gathered, such as "prediction," "proposition," or "assumption." In general, the antonyms for ex-postulate will describe statements that are uncertain or unproven, highlighting the contrast between a statement made before or after an event has taken place.