An Important Criterion for Establishing What Actually Happened

I am in the midst of a threat talking about how historians can use sources such as the Gospels to know what actually happened in Jesus’ life.  These books were not *meant* to provide disinterested historical information about the past, but were quite intentinally slanted accounts meant to encourage and shape faith in Jesus.  They nonetheless do contain important historical information.  How does the historian determine what his historical and what is legendary in them?

Yesterday I gave some o...