A reasonable man holds that the things he believes are true. At the same time, any reasonable man knows that some of his beliefs will turn out to be false, although he knows not which. So the reasonable man holds that some of his beliefs are both true and false. I for one had hoped for more from the reasonable man.
— (Uncertain origin, please let me know if you have any information)
“Quid est veritas?”
— Pontius Pilate
kybernetikos 
Logic is a tool for increasing the number of things you believe in, not for evaulating the truth of beliefs. You will have to choose your own way of determining the truth of a belief, and although some ways are more accepted than others, there is no way to be certain which is the right and which is the wrong way.
Commonly accepted requirements for truth
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