It will rain next Sunday. Is this certain, possible or impossible?
If you say that something is certain to happen, you mean that it will definitely happen. 肯定的; 有把握的
A possible event is one that might happen. 可能 (发生) 的
Something that is impossible cannot be done or cannot happen. 不可能的
Probability is how likely something is to happen. Many events can’t be predicted with total certainty. The best we can say is how likely they are to happen, using the idea of probability.