两者的区别跟形容词 probable 与 possible 的区别一样，probability 表示比 possibility 更大的可能性。如：

War is now a probability rather than a possibility. 战争现在很可能会发生。

Formal talks are still said to be a possibility, not a probability. 正式谈判据说仍有可能，但不是很可能。

A peace agreement now seems a probability rather than a possibility. 达成和平协定现在似乎是十有八九而不只是有可能的事。