We believe that Brian is a lion. We believe that John dropped the apple. It is certain that Lily is a swan.
There is a very good chance that either Lily is a swan, or John dropped the apple.
It is probably not the case that either Lily is a swan, or John dropped the apple.
There is a very good chance that either Lily is a swan, or John dropped the apple.
Either Lily is a swan, or John dropped the apple.