Believe - Hold (something) as an opinion; think or suppose
(definition #5)
- to think, assume, or suppose
(definition #5)
Know - Be aware of through observation, inquiry, or information
(Defintion #1)
- Have knowledge or information concerning
(Definition #2)
If you don't "know" (have evidence to support) some thing you are stating or commenting upon, then you must merely "believe" (be assuming or supposing) that thing. The lack of precision and consistency in your use of language suggests a lack of cognitive discipline and/or acumen, did you graduate from high school?