The cosmological argument is the argument that the existence of the world or universe is strong evidence for the existence of a God who created it.
The existence of the universe, the argument claims, stands in need of explanation, and the only adequate explanation of its existence is that it was created by God.
Like most arguments for the existence of God, the cosmological argument exists in several forms; two are discussed here: the temporal, kalam cosmological argument (i.e. the first cause argument), and the modal "argument from contingency".
The main distinguishing feature between these two arguments is the way in which they evade an initial objection to the argument, introduced with a question: "Does God have a cause of his existence?"
To explain this objection, and how the two forms of cosmological argument evade it, I'll use a simple, generic statement of the cosmological argument:
The Simple Cosmological Argument
(1) Everything that exists has a cause of its existence.
(2) The universe exists.
Therefore:
(3) The universe has a cause of its existence.
(4) If the universe has a cause of its existence, then that cause is God.
Therefore:
(5) God exists.
This argument is subject to a simple objection, introduced by asking, "Does God have a cause of his existence?"
If, on the one hand, God is thought to have a cause of his existence, then positing the existence of God in order to explain the existence of the universe doesn't get us anywhere. Without God there is one entity the existence of which we cannot explain, namely the universe; with God there is one entity the existence of which we cannot explain, namely God. Positing the existence of God, then, raises as many problems as ...