One of the classic arguments for the existence of God. Every event in the natural world has a preceding cause. But this opens up a regress of causes stretching back forever in time. To stop the regress we must postulate a first cause, and this will be the creative action of God. Russell supposed that the argument is uniquely bad, in that the conclusion (that there is a first cause) actually contradicts the premise (that every event has a preceding cause). To avoid his complaint a proponent of the argument must distinguish between natural events and unnatural or supernatural events. The former all require causes, but the latter may be their own cause. God is causa sui. The difficulty then lies in seeing why the natural world should not be causa sui. The argument inherits the problems of the cosmological argument, of which it is a variant.