I'm not sure--------he will come tomorrow.中间为什么不能用whether来连接

朋友,你肯定弄错了.
问题I'm not sure--------he will come tomorrow.中间只能用whether引导宾语从句,因为难以肯定的内容才不确信.
而 I'm sure--------he will come tomorrow中间用that引导宾语从句,因为肯定、明确的内容可确信.
同理：I doubt whether he will come tomorrow和I don't doubt that he will come tomorrow.