Answer: Cosmological arguments attempt to demonstrate God’s existence using the concept of causality. Effects require a cause, and everything we observe in the universe appears to be an effect; therefore, there must be an underlying or primary cause of all things. These arguments typically come in two major types, known as the “horizontal” and “vertical” approaches. The most commonly used form is “horizontal,” also known as the kalam cosmological argument. According to the kalam, there can be only one itself-uncaused-and-eternal thing that causes all other things, and that first cause is God.

The term kalam is Arabic and means “eternal.” The earliest form of this particular argument was formulated by Islamic thinkers. It was also used by Christian philosophers such as the Scholastics. As with any logical argument, some scholars support it and others dismiss it. Unlike less-impactful approaches such as the ontological argument, the kalam remains among the more effective logical arguments for the existence of a Creator.

The kalam claims that each effect requires a preceding cause. If that cause is itself an effect, it has its own preceding cause. This would imply a backwards-facing chain of causality. However, this leads to a logical conundrum: if everything is caused, this chain can never end. But if it never ends, then there would never be anything to begin the chain. A literally infinite series of past events is insensible; it implies a literally infinite time between two moments. Therefore, there must be some point at which the chain of causality “stops”—as we look backwards—or more correctly, where it “begins.”

This can be visualized as a railway train. Each car is being pulled by the car in front of it. The “cause” of movement for any car is the next car ahead. However, if the train were extended forward infinitely, how could it be moving? If the train has an unending succession of cars, then there would be nothing providing force to move the cars. At some point, there must be an engine—something that pulls but is not itself being pulled. Causes and effects can be imagined the same way: for causality to exist, it must begin, and that requires a single un-caused cause.

That single, un-caused, necessary, and unique First Cause would be God. The kalam shows this is not special pleading. The argument does not suggest that “everything” has a cause, only that everything that begins to exist or begins to happen has a cause. The kalam argument is not an attempt to avoid certain conclusions, but is a concession to the only rational conclusion possible. It is basic logic, not doctrine, which suggests there is a First Cause (Psalm 19:1; Romans 1:18–20).

The kalam cosmological argument doesn’t prove, by itself, that the First Cause is the God of the Bible. Nor does it prove that whatever caused the universe to begin is actively involved or personal, or imply that it has any specific properties. The scope of the kalam argument is narrow but extraordinarily powerful: logic itself appears to dictate that there is a First Cause. The nature of that thing is subject to further exploration apart from the kalam.

The kalam cosmological argument is labelled as “horizontal” because it deals with a linear chain of cause and effect. This style of cosmological argument looks at causality from the perspective of mechanisms. For instance, a falling branch lands on a puddle; the resulting splash makes a noise; the noise travels to someone’s ear; the person who hears it turns to see what made the noise. That’s a horizontal line of causality. The alternative to this is the “vertical” sense of causality, which suggests that God is actively and perpetually sustaining the existence of all things. This is significantly more abstract and less useful, and so it is not commonly applied.