Evidence Morphemes ( evidentials )  give the basis upon which a statement is made. They are not required for every statement, only when you wish to make the basis clear. 

ba: I know because I perceived it myself 

bi: I know because it's obvious to anyone

bu: I assume it's true because I trust the source

wobu: I assume it's false because I don't trust the source

be: I know because I percieved it in a dream

bo: I imagine it, it's hypothetical

woba: I have a total lack of knowledge as to whether it's true or not.

The idea for these came from LAadan.