Complex sentence: A third possibility is that indeterminism is true, but our actions are caused by free will, which itself has no deterministic cause, since indeterminism does not necessitate the non-existence of all cause.
Split into simpler sentences: A third possibility is that indeterminism is true, but our actions are caused by free will, which itself has no deterministic cause. Indeterminism does not necessitate the non-existence of all cause.