Why is there something rather than nothing at all? What is the best explanation for the existence of the universe? The famous Philosopher Gottfried Leibniz offers a deductive argument which concludes that the best explanation for the universe's existence is God. The argument is structured in the following way:
1. Everything that exists has an explanation for its existence.
2. If the universe has an explanation for its existence, that explanation is God.
3. The universe exists.
Now, it follows from premises 1) and 3) that:
4. The universe has an explanation.
But premise 2) says, "If the universe has an explanation of its existence, that explanation is God." Therefore, it follows that,
5. God is the explanation for the universe.
Since this is a deductive argument, it means that if the premises are true, the conclusion is necessarily true. In other words, there is no escape from the logical conclusion of the argument. Now, this puts skeptic in a tough spot. Unless the skeptic believes the universe is an illusion of the mind he will not deny premise 3. Therefore, the proponent of the argument needs to defend premises 1 and 2.
Defense of Premise 1
In defense of premise 1, I'd like to offer a thought experiment. Say you were hiking through the woods with a friend and came across a translucent basketball. You may ask how such a ball came to exist. But say your buddy stated, "Oh! Look! A ball! It exists without explanation!" It would probably be safe to say that your friend is simply trying to get to their destination quickly or doesn't care about the question of the ball's existence.
But what if you increased the size of the ball to the size of the state of New York? The problem still needs to be solved. Now what if you increased the size of the ball to that of planet Earth? What about increasing the size of the ball to that of the universe? See, no matter how big the ball becomes, it does nothing to impact the need for an explanation.
This is what the first premise of Leibniz's argument suggests: That everything that exists has an explanation of its existence. There is just no reason to exclude the universe.
Defense of Premise 2
What about the claim of premise 2, What good reasons do we have to believe it is true?
Well, since the universe, as defined in this argument, is all physical space-time reality, the cause of the universe must transcend space and time and therefore is not physically material. Only two types of things could fit this description: (i) abstract objects or (2) a mind. Yet, abstract objects do not stand in causal relation. The number 22 can't be the explanation for anything's existence. Therefore, the only thing that explains the universe's existence is a transcendent unembodied mind or what most people have traditionally called God.
Conclusion
Assuming that skeptic doesn't attack premise 3 and without any defeaters for premises 1 and 2, it logically follows that the universe has an explanation for its existence, and that explanation is God.