The relation of necessary consequence to that which requires it is not identical in every respect to an ordinary causal connection. For instance, a given effect might have several causes, while a genuinely necessary condition has a different logical role.
RelationIllustrationCaution
Cause / effectOne cause produces an outcomeOther causes may exist
Necessary conditionAnother fact is required for a resultIdentify the direction of necessity
Read an example of law with attention to whether it asserts a causal explanation or draws a specific inference. Without that distinction the argumentative force is liable to be reversed.