How can we know if God is real? How can we know anything?

Extreme skepticism is a form of philosophical skepticism that considers it impossible to believe anything (1). Where atheists claim that we have not proved that God exists, an extreme skeptic would say, “We cannot prove that anything exists.” Some would take this to imply that God's existence and non-existence are equally likely.

At its mildest, extreme skepticism raises the question of whether any particular view can be proven or considered objectively correct. In its strongest form, such skepticism can lead to a total rejection of the physical world. As a philosophical quandary, skepticism of this kind has existed for thousands of years (1).

How Can We Know Anything?

Before showing why this argument cannot be used to counter atheism, it helps to understand exactly what is meant by skepticism in this sense. The reason that some claim that true knowledge is impossible is because we are limited by our senses and experiences, which are ultimately subjective. We perceive reality through our senses and think about it with our brains, and it’s impossible to know for sure whether these senses are actually trustworthy.

For example, consider the color blue. We understand scientifically that the color is caused by a specific wavelength of light bouncing off of an object, and we can measure the length of waves to determine whether a color can be classified as blue. We cannot, however, say with absolute certainty that the color we perceive as blue actually looks the same to anyone else. Because we cannot see through other people’s eyes, we can’t know for sure how colors look to them.

Indeed, it’s possible that we do not even really exist and that there is no such thing as reality. We could all be brains in vats, hooked up to a computer simulation, like in the famous movie The Matrix; everything you know and experience may be a lie. As the logic of this argument goes, we have no way of knowing whether we’re actually brains in vats; therefore, we have no way of knowing anything else about our world. Since this claim is in no way testable, however, we have no way of proving it and no reason to believe that it’s true. We can only live in the reality we can observe, not a hypothetical reality that we have no way of proving. To do otherwise would be insane. 

For example, imagine that someone tells you that there is a monster living beneath your bed. You can never know that he’s there, however, because he is invisible, makes no noise and leaves no trace of his existence. Since there is no way of proving that such a monster exists and since its existence is very unlikely given that it contradicts many highly predictive scientific models explaining our universe, there is simply no reason to act as though there’s a monster under your bed. Since such an unfalsifiable monster is indistinguishable from a monster that doesn’t exist, it is most practical to simply live as though there is no monster.

Are you currently awake, or is this a dream? Maybe you are still in bed. Maybe when you wake up, you’ll remember that you are not even who you think you are at this moment in your dream. You might have a different name, gender or race. You might not even be human. Or you might be just a character in someone else’s dream or an advanced computer game. And once whoever is dreaming this dream wakes up or turns off the gaming console, you would cease to exist. You can’t prove any of this is not true, but would it be reasonable to make any decisions based on these or the unlimited number of other unfalsifiable claims?

We do not require absolute certainty about our world. We can act on the information available to us, making the best choice possible with what we can know with some but not an absolute level of certainty. Such levels of certainty are sufficient for us to act upon. Science doesn’t claim to have absolute certainty about the world; it creates models that provide the best explanation based on the available evidence. If additional evidence is found, the model can be changed. Religious claims should stand up to the same scrutiny as scientific ones; claims should be testable, repeatable and falsifiable. If there is no way to test whether a claim is true, there is no reason to live as though it is. 

Beliefs Can Be Justified

We have no choice but to live in reality and obey the laws that govern it as they are perceived. Even if our reality were only a simulation, it’s the only option available to us, and so we base our beliefs about the world on what we can observe. We don’t wait until we have absolute certainty before acting; we make decisions about our world based upon what our experiences can tell us of the laws of our universe.

Carl Sagan once said, “Extraordinary claims require extraordinary evidence.” If you make a claim that does not contradict our current understanding of the universe, some basic level of data would be sufficient to support it. For example, if you claim that the sun will rise around 6 a.m. tomorrow, I could be inclined to believe you. Depending on the time of year and geographical location, I could determine whether your claim is consistent with what I could expect. If, however, you tell me that the sun will not rise tomorrow and will instead be eaten by a giant wolf in the sky, I’ll need significantly more evidence. Everything I can observe about reality suggests that this is incredibly unlikely, as it disregards many apparent laws of the universe. Before I could accept such an extraordinary claim, I would need some very compelling evidence. Otherwise, it would be much more likely to assume that you were insane or simply lying.

Saying that we can’t really know whether God exists does nothing to prove that it does. Not being able to know something for certain does not increase the odds of it being true. Unlike extreme forms of skepticism, scientific skepticism evaluates the likelihood of a claim by the strength of the evidence supporting it. Using such methods, we can assess the likelihood of claims. Unfalsifiable claims, such as God, Santa Claus or leprechauns, are not as likely as claims with strong testable, verifiable and repeatable evidence (2). Time and again, the scientific method has, more consistently than any other method, been successful at providing explanations with very accurate predictive power for our universe. This can easily be seen in the success of technological advancements in the past century and has justified belief in the stability of natural laws.

I Reject Your Reality and Substitute My Own

On the TV show Mythbusters, Adam Savage famously quipped, “I reject your reality and substitute my own” (3). He was joking, but the sentiment is one that can be easily applied to people who subscribe to extreme skepticism: if we cannot truly know anything, then anything could be true.

While there may be merit in discussing such ideas from a philosophical standpoint, it doesn’t hold water as an argument for the existence of God. If we accept this argument as true, then we also cannot be certain that this argument is correct, as certainty would refute the very basis of the argument. 

All of this philosophizing is really just a distraction from the fact that theists cannot prove the existence of their god. It is not the burden of atheists to defend their lack of belief, and atheists do not need to have all of the answers about the world in order to lack belief in a deity. Theists, by claiming that God exists, are making an extraordinary claim. This requires extraordinary evidence. That evidence does not exist. No argument laid out by theists so far is compellingly believable.


  1. Dancy, Jonathan, Ernest Sosa, and Matthias Steup, eds. A Companion to Epistemology. 2nd ed. Wiley-Blackwell, 2010.
  2. Kurtz, Paul. The New Skepticism. Prometheus Books, 1992.
  3. Savage, Adam. "Explosive Decompression/Frog Giggin'/Rear Axle." MythBusters. Discovery Channel. 11 Jan. 2004.

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