Does God Exist?

Start here: the train with no engine

Picture a long goods train rolling past a level crossing. Each carriage is pulled by the one in front of it. Carriage 50 moves because 49 pulls it; 49 moves because 48 pulls it.

Now suppose someone tells you there is no engine: just carriages, going back forever. Would the train be moving?

No. Every carriage only passes on motion it receives. Add more carriages, even infinitely many, and you still have nothing that starts the motion. Somewhere there has to be an engine.

That simple idea sits at the heart of the most famous arguments for God’s existence ever written.

Can reason know God exists?

Some people think belief in God is purely a matter of feeling, or of faith with no reasons at all. The Catholic tradition disagrees. It has always taught that the existence of God can be known with certainty by the natural light of reason, from the things that have been made.

St Thomas Aquinas gave five arguments, known as the Five Ways. Each starts from something we can observe in the world and reasons back to its cause. We’ll look closely at the first three.

The First Way: from change

1. Things in the world change. (We see this every day.)
2. Whatever changes is moved from potency to act by something already in act. (Lesson 4: the acorn needs sun, soil and water that are actually there.)
3. That mover, if it is itself being changed, needs a mover too.
4. This chain cannot go back forever, or nothing would be moving now. (The train needs an engine.)
5. So there must be a First Mover that is not moved by anything: pure act, with no potency at all.

And this, Aquinas says, everyone understands to be God.

The Second Way: from causes

The Second Way follows the same pattern with efficient causes. Things are brought about and kept in being by causes. A lamp gives light because electricity flows; electricity flows because a generator runs; the generator runs because…

Notice that this is a chain of causes acting right now, not a timeline stretching into the past. The question isn’t “what happened first?” but “what is holding all of this in being at this very moment?” A chain of dependent causes, each borrowing its power from the next, must end in a First Cause that is uncaused.

The Third Way: from contingency

Everything around you is contingent: it exists, but it could have not existed. You, your house, the sun and the stars all depend on other things for their existence.

If everything were contingent, there would be no explanation for why anything exists at all. So there must be at least one necessary being: something that cannot fail to exist, whose existence depends on nothing else, and on which everything contingent ultimately depends.

The Fourth and Fifth Ways, briefly

• The Fourth Way notices that things are more or less good, true and noble. “More” and “less” imply a standard, so there must be something that is good, true and noble to the highest degree.
• The Fifth Way notices that natural things without minds act regularly for ends (acorns become oaks, eyes see). Purpose without a mind points to an intelligence that directs nature.

”But who made God?”

This is the most common objection, and it rests on a misunderstanding. Aquinas never says everything needs a cause. He says that things which change, which are caused, or which are contingent need a cause.

His conclusion is a being that does not change, is not caused and is not contingent. Asking “who caused the uncaused cause?” is like asking “what is north of the North Pole?”

Reason and faith

These arguments show that there is a First Cause: one, unchanging, necessary and the source of all things. Reason can go further and show that such a being must be perfect and good.

But reason alone cannot tell you everything. That God is a Trinity, or that God became man in Jesus Christ, are truths we know because God has revealed them. Reason prepares the way for faith; it does not replace it.

Read the texts

Read Summa Theologica I, q.2, a.2 and a.3. As you read the First Way, try mapping it step by step against the train example. Ask:

1. Which step of the First Way do you think a sceptic would most likely challenge?
2. Why does Aquinas start from things we can see rather than from the idea of God?