Dr Ben Holloway, Professor of Philosophy and History of Ideas, Southeastern Baptist Theological Seminary

“Are you certain?”

You wonder how to reply. Suppose you say no. Your friend might say, “Well I didn’t think so. Christianity is just a leap in the dark.” Suppose you say yes. Doing so will oblige you to defend your beliefs as being certain. But you don’t feel able to defend them to that degree.

Being certain about our Christian beliefs is something we all want. But what exactly is the worry about? In this post, I will try to explain how certainty plays a role in scepticism, the view that there are some things (perhaps all things) we can’t know. I will show one way of avoiding one particularly extreme version of skepticism that will involve denying that knowledge requires certainty. I will then introduce another kind of certainty and then use all that I have said to explain a good way to answer your friend’s question.

First, return to a story I told you about in my first post.

When I was seven years old, I was sent to boarding school. Perhaps because I would rather not have gone, I began to use my imagination to escape. At some point, I began to wonder if what I was experiencing was real. I considered the possibility that I was not at school but was in a laboratory hooked up to a machine capable of inducing illusions in my mind. Perhaps what I thought was real—being at school—was my imagination and what I was imagining—being in the laboratory—was what was real. A question then occurred to me: how could I know which version of my life was real?


It turns out that my imagination had struck upon a scenario of philosophical significance. Other philosophers have considered whether it would be possible to distinguish having a dream and experiencing reality (Descartes), or whether one can rule out the possibility that we aren’t just brains in vats hooked up to a computer.

Whichever way the scenario is configured, it poses a problem for anyone who thinks we can know about the world. Imagine discovering that you are not really in the world and that nothing has ever really happened to you. Instead, you are a brain in a vat of preservative. Your brain is attached to all sorts of wires that are connected to computers. All your life experiences turn out to be the result of a series of computer-generated stimulations. Thus, you don’t really know anything about the world. You only think you do.

How should we avoid the threat of this kind of scepticism? One way would be to argue that you are not a brain in a vat. If you could show that you are not a brain in a vat, then the threat would go away.

An argument might begin by suggesting that if you can be certain that you have arms, then you’re not a brain in a vat. We can all be sure of that. It doesn’t rely on any knowledge of the external world. It just says that if I have arms, then I am not a brain in a vat. It would follow from knowing that you do in fact have arms that you would know that you are not a brain in a vat. Thus, you could avoid the terrible conclusion that it is possible that you are merely a brain in a vat. You might try to show you have arms by holding them out in front of yourself and saying, “See! There they are!”

However, the sceptic argues that you cannot be certain that you have arms. How could you possibly know whether what you are experiencing is genuine or merely the result of a computer simulation? The argument demonstrates that knowledge of the external world is never guaranteed. It is always possible that you are a brain in a vat.

At this point, the conversation has reached an impasse. Hence, another strategy is required to combat the threat of scepticism.

To see how to avoid the conclusion, consider the basic argument the sceptic makes. It begins by suggesting that any belief about your perceptions of the world could be mistaken. You could be wrong. You could be dreaming or just seeing what the computer makes you see. This seems clearly true. We can’t absolutely rule it out. The sceptic then suggests that if you can’t be certain about something, you don’t know it. For example, if you can’t be certain that you have arms, you don’t know that you have arms. The conclusion follows: you don’t know anything about the world.

What’s wrong with the argument? We’ve conceded the first point. We could be wrong about what we see and hear. But what about the next one? Is it really true that if we can’t be certain about something, then we don’t know it? It is at this point we have a way to fend off scepticism. You don’t have to be 100% certain in order to know it.


To adopt the suggested strategy is to embrace fallibilism. A fallibilist thinks that our justification for beliefs does not require 100% certainty. Instead, good reasons for beliefs are enough to justify them even if there remains the possibility of being mistaken. One can even be only 60% certain of a belief and it will still be justified, although weakly. The fallibilist view aids us in responding to skeptics deploying the above argument.

Applied to the brain-in-a-vat scenario, it is not a condition upon my belief that I am not a brain in a vat that it must not be possible that I am brain in a vat. I can accept that it is possible that I am a brain in vat. It doesn’t follow from that that I don’t know anything.

Now, for the original argument to work, the sceptic must show that you are in fact a brain in a vat. Lacking any evidence at all for such a situation, you are free and clear to continue believing that you are not a brain in a vat. Such a conclusion would have served as a relief to the seven-year-old me!


It may come as a surprise that our beliefs about the world aren’t 100% certain. Surely some of them are. Two things might be said. First, the beliefs in question are limited to those about the empirical world, the things we can observe. They include the ordinary beliefs we have such as your belief you have arms. But they also include beliefs about what happened in history. Other beliefs appear to have near or complete certainty, but they aren’t the kind of beliefs reliant on perception. Beliefs such as anything coloured takes up space can’t be doubted easily. Even a brain in a vat is justified in believing it! Hence, we are only talking about what we might call ‘empirical beliefs’, beliefs reliant on the produce of our perceptive faculties.

Second, even if empirical beliefs are not 100% certain—we could be mistaken—this doesn’t alone entail that we can’t have another kind of certainty about them. For, as Ludwig Wittgenstein points out, beliefs can have maximal justification for the kind of beliefs they are. For example, perceptual beliefs can be very clearly true. I can admit that they might be false. I could be dreaming. So, perhaps they can only have 90% justification. But still, given that that is the best I can expect for that kind of belief, I don’t have to worry about them being false. I can have a psychological commitment to them equivalent to the kind of commitment I can have for the belief that 2+2=4.

Such a distinction is important for Christian beliefs. Most Christian beliefs are about events in history that we derive from the accounts given in the Bible. On a fallibilist view, historical beliefs are never 100% certain. They could be false. Does that entail that you should doubt them? Not at all. They have a sufficient degree of support rendering them as justified as they could be. Hence, one can be 100% committed to them even if their evidential support only gives them 90%. Hence, one can have maximal psychological certainty for beliefs about the history of Israel and the life of Christ.

How to Answer the Question

Any demand for certainty presents a kind of practical dilemma for the Christian. If you say you aren’t certain, you can be accused of a kind of blind faith. If you say you can be certain, then there is demand for an absolutely irrefutable argument, which most of us feel unable to provide.

What I have suggested so far allows an answer to deal with both sides of the problem. The first thing to say is that most beliefs don’t require certainty for knowledge. You don’t have to provide an irrefutable proof for the occurrence of events in the past. You must only provide enough evidence to make it more likely to have occurred than not. Hence, a Christian does not have to supply any argument for historical beliefs about God’s actions in history that are irrefutable. You only have to supply good arguments that sufficiently support your claims. This is eminently more doable.

Further, just because historical beliefs don’t get certainty from evidence, it doesn’t follow that you have to be less committed to them than more certain beliefs. Christian convictions are such that we can feel psychologically sure about them. So sure, in fact, that we’d never deny them no matter what the cost. This is because psychological certainty can outstrip the evidence. Christians don’t have to be racked by doubt over their beliefs. They can have a confidence in them that will be sustained by the Holy Spirit even when the cost for having them is high.

Descartes writes about the possibility of his experiences being a dream in Meditations on First Philosophy, meditation I (1647). Brains in vats are discussed by Hilary Putnam in “Brains in a Vat,” in eds. Sven Bernecker and Fred Dretske Knowledge: Readings in Contemporary Epistemology (New York: Oxford University Press, 1999), 1–21. For an argument for having arms, see G. E. Moore’s essay, “Proof of an External World” in Philosophical Papers (New York: Collier Books, 2959). Richard Feldman gives an explanation of fallibilism in his paper, “Fallibilism and Knowing that one Knows,” Philosophical Review 90 (1981): 77–93. For a discussion of certainty, see Ludwig Wittgenstein’s book On Certainty (New York: Harper, 1969). I was introduced to Wittgenstein’s way of handling certainty by John Feinberg. He describes it in chapter 6 of Can You Believe It’s True? (Wheaton: Crossway, 2013).