The great German philosopher Immanuel Kant (born April 22, 1724) is perhaps the most well-known philosopher of the modern era. Among his many works was a book titled Critique of Pure Reason, which he wrote in 1781. The work is an analysis of purely theoretical arguments, or proofs, for metaphysics or for the existence of God. Two proofs in particular receive significant attention in the work: the cosmological and teleological arguments. Kant attempts to dismantle these arguments, but in a later work he ends up contributing a proof of his own.

The cosmological argument has to do with the cosmos—the world—and the law of cause and effect. The law of cause and effect is that for every effect there is an equal or greater cause. The cosmos is an effect, so there must be a cause behind it. The existence of the world points beyond itself to a source, that is, a Creator. Kant’s response was to say that we cannot extrapolate from our experience with cause and effect to the realm of metaphysics, the realm beyond our physical experience. In other words, we cannot use the law of cause and effect to prove the existence of God.

Kant also attempted to dismantle the teleological argument. The teleological argument builds upon the cosmological argument. Teleological is rooted in the Greek word telos, which means “end,” referring to a design or purpose. The teleological argument states that the world reveals and reflects significant and complex design and therefore points to an intelligent designer.

So, Kant attempted to dismantle the cosmological and teleological arguments, but despite his critique, these arguments didn’t go away. They are still used today, and they have a place in pointing us beyond this world and pointing to a Creator. But Kant sought to make a different argument for metaphysics and the existence of God.

In 1788, he published his second critique, the Critique of Practical Reason. The first chapter contains Kant’s moral argument for the existence of God. The argument is based on what Kant called “the categorical imperative,” which he stated like this: Act in such a way that your action can become a universal law. In other words, Kant believed that we are all bound and obligated by morality. In fact, Kant went on to say that the proof that God exists “is the starry heavens above and the moral law within.”

In the twentieth century, C.S. Lewis used the moral argument for the existence of God in Mere Christianity. He begins by saying that there is a universal moral law, and at one point he writes: “There is nothing indulgent about the Moral Law. It is as hard as nails.” Perhaps saying that there is a universal moral law prompted Lewis to ask, What lies behind the law? The answer is that behind the law is a Lawgiver. We cannot get rid of the moral law, the “oughtness” that we all have universally, and that moral law points beyond the existence of this world and the phenomena of experience to God.