How to translate belief?
I would say:

知識是一種信念, 但信念不必是知識.

I thus translate it because of the following reasons.

1) A belief is something that is not tested or proved. 

2) Knowledge in natural sciences is something that passes lots of tests. But, it is still to a certain extent a belief; for there is no way to be sure that knowledge in natural sciences will not be disputed by new evidence. 

Therefore, knowledge can be viewed as the collection of tested beliefs.