Everything that begins to exist has a cause. The universe began. So what caused it?

The Kalam argument runs in three short steps: everything that begins to exist has a cause, the universe began to exist, therefore the universe has a cause. Islamic theologian Al-Ghazali formulated it in the 11th century to argue against philosophers who claimed the universe had always existed. Philosopher William Lane Craig revived the argument for modern academic debate in his 1979 book, and it remains one of the most actively contested arguments in philosophy of religion.

— William Lane Craig (modern revival); Al-Ghazali (medieval formulation), The Kalām Cosmological Argument — Craig, 1979; Al-Ghazali, 11th century