The rule, in one sentence
Two statements contradict when both cannot be true at the same time in the same sense. Anything less than that is a difference.
The rest of this step93 words
One account says the women found the tomb empty at dawn; another says while it was still dark. That is a difference: dawn and dark overlap, and people describe the same hour both ways.
One account says Jesus died and stayed dead; another says he rose. That would be a contradiction. There is nothing like that in the Bible, which is why nobody argues about it.
Almost every case you will meet lives in the space between those two, and the whole skill is learning to tell where in that space it sits.
