 One persistent worry about the sole-source thesis has its roots in the medieval debate over whether there is secondary causation (i.e., genuine causation by created things). Suppose that created things are causes: fire really does cause water to boil, and ice really does cause it to cool. If creatures can affect future events in this way, why should they not at least help to bring about their own future existence? Why should their causal powers be limited to affecting the qualities of things without contributing to their own presence in the world? Contrapositively, if created things cannot bring about their own future existence, are they also unable to have any effect on the future?