Cause and effect
Nietzsche on necessity:
Against determinism and teleology.-- From the fact that something ensues regularly and ensues calculably, it does not follow that it ensues necessarily. That a quantum of force determines and conducts itself in every particular case in one way and manner does not make it into an "unfree will." "Mechanical necessity" is not a fact: it is we who first interpreted it into events. We have interpreted the formulatable character of events as the consequence of a necessity that rules over events. But from the fact that I do a certain thing, it by no means follows that I am compelled to do it. Compulsion in things certainly cannot be demonstrated: the rule proves only that one and the same event is not another event as well. Only because we have introduced subjects, "doers," into things does it appear that all events are the consequences of compulsion exerted upon subjects--exerted by whom? again by a "doer." Cause and effect--a dangerous concept so long as one thinks of something that causes and something upon which an effect is produced.