It’s a basic topic, but an important one: how do you know that God exits? Many people are unable to articulate a convincing answer to this. This doesn’t make such a person’s faith wrong; personal experiences of God can be hard to articulate and are normally not verifiable, requiring one to trust the words and experiences of another human being. These experiences are still valid proof for an individual, but don’t make good arguments. How can we construct a good argument for the existence of God for someone who has not had these experiences?
I’m going to take a stab at it, using St. Thomas Aquinas (a great medieval thinker) and C.S. Lewis (a 20th century atheist who converted to Christianity and became a famous apologist.)
All That Is
The best argument starts from the tangible universe. Every effect has a cause, and every cause has an effect. ‘Why is this book here?’ leads us back through chains of causation that will eventually take us into distant history – the printing press – the first alphabets and even further back to the origin of communication abilities and beyond. Eventually, we come to a time where we can only guess at causes. We draw a blank, and there are two suppositions made about this “blank”: one is that it contains more causes and effects, in an infinite chain; another that this is where the chain stops and its origin or “first cause” is.
Let’s take a look at the former claim. Is it possible that this chain of cause and effect is infinite? No. Let’s go back to our book. Suppose that it’s lying on the table in front of you, and there are an infinite number of things you need to do before reading it. Even if you lived forever, would you ever read the book? No, there simply isn’t enough time (no matter how much of it you have.) In such a universe, we wouldn’t have enough time to get to the way things are now. This chain of causes needs to have a finite number of links leading to a “First Cause.”
This “First Cause” cannot be part of the chain of causation. If it were, it would be subject to the same rules that everything else in the chain is, principally that each thing must have a cause. (This rule is also why even an infinite chain demands a First Cause for its own existence.) So our First Cause is something outside of the tangible universe, itself uncaused and outside the chain of causation.
Determining What Our “First Cause” Is
Some additional details can be determined about our First Cause by looking at the universe that this cause has put into effect. There’s an intelligible pattern to the way that the universe works, suggesting that the First Cause itself has some sort of logical structure. The fact that we are able to comprehend the logical structure of the universe suggests that our minds have something in common with that First Cause, at least in part. The universe is constantly in motion or changing, both of which need something to start that motion or change without itself being moved or changed (for the same reasons that our cause and effect chain can’t be infinite and need an uncaused First Cause.)
It’s also possible to start with the internal convictions of mankind rather than the tangible universe. Everyone in the world (except a psychopath) buys into the existence of the intangible categories of things that are right and things that are wrong. To be clear, people don’t always agree on what constitutes right and wrong, especially once we come to technical questions, but that’s not essential for our argument. The mere fact of supposing that these categories exist supposes the existence of someone with the authority to define these categories.
Otherwise, right simply becomes “the category of things that I personally approve of.” (One might also say the category of things that are legal, or that society approves of and so on.) By the same token, wrong becomes the category of things that one disapproves of. Genocide becomes, in the final evaluation, wrong only in the same sense that earwax flavored Jelly Beans are. Slavery is wrong only when prohibited by law or custom, and only to the degree that speeding is. Morality becomes relative, with no way to pass anything other than a personal judgement on the validity of one’s actions. For right and wrong to have absolute weight, there needs to be an objective Authority that has made it so.
Classically, Christianity asserts that this First Cause, this Authority on right and wrong, is God. These arguments tell us that God is unmoved, unchanging, works in an intelligible way, is the creator of all things and the one who delineates right and wrong. This is far from a validation of all that Christianity teaches about God. This does not, for example, teach us that God is loving, actively involved in our current world or a Trinity of persons. Any monotheist could embrace these arguments. It is, however, an important first step: these arguments can give us a rational certainty that God is for real.