The first cause is the postulate, popular in philosophy and theology, that, since everything that happens must have a cause, everything is traceable back to a first cause, usually referred to as God. A popular argument for atheism - along with being a popular scientific rebuttal of intelligent design - is the notion of the infinite regress. Every action or being requires a cause, so if God exists, God must have a cause; that cause also had a cause, and so on, literally ad infinitum.