Cosmological arguments all try to explain why anything moves, changes, or exists at all. But there are different versions of the argument with subtle differences.
Some are arguments from contingency – they focus on the fact that the universe didn’t have to exist, and so argue that a necessary being (God) must exist to explain why anything exists at all.
Others are arguments from causation – which is what this post is about. These versions say that everything that begins or changes must have a cause, and since there can’t be an infinite chain of causes, there must be a first cause (God).
But within these cosmological arguments from causation, there’s an important difference – the direction of causation:
- Horizontal: These arguments look backward through time, tracing a sequence of causes and effects until they reach a starting point in time.
- Vertical: They look through the hierarchy of causes in the present moment to explain what keeps everything going.
Horizontal cosmological arguments (e.g. Kalām)
Horizontal cosmological arguments work by tracing a sequence of causes or explanations backwards in time to a first cause, first mover, or necessary being: God.
The Kalām cosmological argument is a classic example of a horizontal argument:
- Whatever begins to exist has a cause
- The universe began to exist
- Therefore, the universe has a cause
This argument says the universe can’t have just popped into existence from nothing – because nothing comes from nothing: Whatever begins to exist has a (prior) cause.
For example, the sequences of causes leading to someone boiling a pot of water could be traced back like this:
- The water is hot
- Which was caused by someone putting the pot of water on the fire
- The fire was caused by the person lighting a match
- They struck the match because they wanted to boil water for coffee
- …
- The person was caused to exist by their parents
- …
- The person’s parents were caused to exist by their grandparents
- …
- The Earth formed
- … 13.8 billion years of causes…
- The Big Bang
- ???
Eventually, you reach a point where you can’t just keep going backward forever. The Kalām argument says that an infinite regress of causes is impossible. So at some point, you need a first cause – something that causes but isn’t itself caused: God.
So, horizontal cosmological arguments like the Kalām argument are about the origin of the universe in time. These arguments say there must have been a first cause at the very beginning (before even the Big Bang) and that this first cause is God.
Vertical cosmological arguments (e.g. Aquinas’ 2nd way)
Where horizontal arguments like the Kalām argument are about the chain of causes stretching backwards in time, vertical cosmological arguments are about the chain of causes that explain things in the present moment.
St. Thomas Aquinas’ 2nd way is often interpreted as a vertical cosmological argument:
- The world is full of causes and effects
- Nothing can cause itself
- Every cause needs a prior cause
- If this sequence goes on forever, there’s no first cause
- But if there’s no first cause, there’d be no causes at all
- But we know causes exist
- So there must be a first cause
- And this first cause is God
This might sound a bit like the Kalām argument at first because it also talks about a chain of causes. But where the Kalām argument talks about a sequence of causes stretching backward in time – a horizontal chain – Aquinas is talking about a vertical chain of causes happening right now – a vertical hierarchy of dependence in the present moment.
So again, using the example of a fire heating a pot of water:
- The water is hot
- Because of the pot
- Which is hot because of the fire
- Which is burning because of a chemical reaction
- Which is possible because of the structure of atoms and the laws of physics
- And so on.
All of this is happening simultaneously. Each level is dependent on the one above it, in the same moment.
Aquinas argues that this kind of stacked, real-time, sequence of causal explanations can’t go on forever either. If everything is dependent on something else, then the whole system would be suspended on nothing, and that’s impossible.
So, vertical cosmological arguments like Aquinas’ 2nd way are about the chain of causes in the present moment. At every moment, each cause depends on something else to sustain it. This means there must be a fundamental, uncaused cause at the top of this chain – something that isn’t caused by anything else but keeps everything else in existence. And this first cause is God.
Horizontal vs. vertical cosmological arguments
Both horizontal and vertical cosmological arguments try to explain what causes reality to exist and why it doesn’t collapse into nothing. But they ask different questions:
- Horizontal arguments (like Kalām) ask: How did everything begin? They trace a timeline of events back and argue that the universe must have had a beginning – and so a first cause.
- Vertical arguments (like Aquinas’ 2nd Way) ask: What is sustaining everything right now? They look at the present moment and argue that even if the universe had no beginning, it still needs a foundation – something that causes but is not caused.
Modern science can be used in support of horizontal arguments. According to the standard Big Bang model, space, time, matter, and energy all came into existence around 13.8 billion years ago. This is based on observations like the expansion of the universe, which if you extrapolate backwards points to a definite starting point in the past. So if this is when the universe began to exist, and whatever begins to exist has a cause, then we need a first cause to explain the universe.
However, the Big Bang model describes the universe after its earliest moments. What happened at – or before – the Big Bang is unknown. Physics breaks down at that point and several alternative models have been proposed such as the oscillating universe model where the universe infinitely expands and contracts. If such a view is correct, the universe may not have had a beginning in time at all – it is eternal and so doesn’t have a first cause.
This is where vertical cosmological arguments come in. They don’t ask what started the universe – they ask what sustains it. Aquinas’ point is that a chain of causes in time wouldn’t be enough to explain why anything exists right now. The continued operation of the laws of physics, the persistence of matter, and the stability of reality itself all seem to depend on something deeper. An eternal universe still needs a sustaining cause – something that explains why causes keep causing.
But whether the universe had a beginning or has always existed, both kinds of cosmological argument – horizontal and vertical – agree that there has to be an ultimate cause of reality: God.