Subscribe to 18Forty's NEW PODCAST "18 Questions, 40 Israeli Thinkers" on Apple, Spotify, or wherever you listen


What Makes Beliefs Rational?

When can we take belief in God for granted? And does that make us irrational?

This is the second essay of 18Forty’s new “Faith in Reason” series with Rabbi Steven Gotlib, released every month. Sign up for it here, and read the first essay here.

The ultimate goal of this series is to demonstrate that many of Judaism’s core assumptions can be part of a reasonable worldview. Such a perspective need not be stereotypically rationalist, but it should be able to withstand serious intellectual scrutiny. As my teacher Rabbi Dr. Sam Lebens said in his 18Forty interview, “I don’t recognize a hard and fast distinction between mysticism and rationalism. I recognize a hard and fast distinction between bad philosophy and good philosophy.” Indeed, if one digs deeply enough, they can find that figures assumed to be staunch rationalists—such as Descartes, Spinoza, and Maimonides—were deeply mystical in their own ways. Given that, this series will follow Lebens’ example and use “rationalist” and “mystical” sources largely interchangeably – provided that such sources are sound. Before examining any sources, though, we must answer a more basic question: What does it mean to be rational?

What Is Rationality? Epistemic and Practical

Rationality itself has many faces and interpretations. Recently, many religious thinkers have noted and utilized the distinction between epistemic rationality on the one hand and pragmatic or practical rationality on the other. 

In Lebens’ formulation, something is epistemically rational to believe if it corresponds to evidence while something is practically rational if it is reasonable “given your interests, given your makeup, given what you believe, but also given what you want.” There is a big debate in philosophy as to what degree practical rationality should influence decision-making over epistemic rationality, but overall “pragmatic encroachment on epistemology” is rather controversial. While it is intuitive that decision-making takes both forms of rationality into account, one still needs an epistemic base for the decision to make sense, and one should not simply choose to do or believe something because it is convenient for them. Lebens uses the example of seeing a movie: 

Depending on whether you want to see a comedy, or a tragedy, or an action movie, different things will be rational… It’s rational for you to go and see film X if you’ve been told reliably that it’s a comedy, therefore you believe it’s a comedy, and you want to see a comedy. It wouldn’t be rational if you believed it was a tragedy and you want to see a comedy. So beliefs are relevant to practical rationality, but they’re not the only thing. So you ask me. What would I be saying pedagogically, at the beginning of the conversation, with somebody, I guess in their 20s thinking about, is [Orthodox Judaism] for me? I’d ask them to think about first of all, what’s in their practical interest?

Of course, if there are 10 movies playing in the theater, you want to see a comedy, and three of them are comedies then there are only three practical options to choose from. If one was to pick a fourth movie thinking it’s a comedy only to find out that it is, in fact, a horror film, they would leave that theater immediately and try a different one. And if one’s friend tried to talk them into seeing a different movie, but it was not a comedy, they would not want to watch it in the first place. Therefore even our practical decisions need to be backed by epistemic confidence that what we are doing is, in fact, in line with reality in the first place. Someone can still choose to see a different type of movie if they want to, but doing so would require rejecting their original desire to see a comedy. 

When one switches from discussing movies to discussing religion, the problem becomes clearer. 

Applying Rationality to Religion

If someone is Jewish for practical reasons, they may still be able to take it fairly seriously, but they can easily say “I feel like I want to try something different today” unless there is sufficient epistemic reason for Judaism to be compelling to them—independent of the practical factors. The question, then, is how we can be reasonably sure that our beliefs align with the truth of reality to begin with. 

This is most reliably achieved through appealing to Bayesian Reasoning. In his book, The Big Picture, Atheist cosmologist Sean Carroll explains how this works using the imagery of jars of sand corresponding to different beliefs that someone can hold: 

The credence of proposition X is the number of grains of sand in jar X divided by the total number in all the jars. What this procedure does is to re-weigh the prior credences by the likelihoods, in order to obtain posterior credences. We might start with a situation where several jars have approximately the same amount of sand, corresponding to equal credences. But then we obtain some new information, which would be likely under some propositions and unlikely under some other ones. We remove just a little sand from the jars where the information was likely and a lot from those where the information was unlikely. We’re left with a relatively greater amount of sand in the more-likely jars, corresponding to greater posterior credence for those propositions. Of course, if our prior credence in one proposition was incredibly large compared to that for its competitors, we would have to remove a very large amount of sand (collect data that was very unlikely under that proposition) for that credence to become small. When priors are very large or very small, the data has to be very surprising in order to shift our credences. 

The natural issue with this sort of reasoning is that it is impossible to reach complete certainty about anything. Despite that, though, we can still aim to know things with a high degree of confidence (credence) and remain open to reassessment based on new information. At the end of the day, Carroll notes that we are left with “not absolute proof of anything, but a high degree of confidence in some things, and greater uncertainty in others.” 

Given that reality, how much credence does one need to be able to assign in them to justifiably believe in religious propositions (God, revelation, etc)? A natural way to think about it could be having a preponderance of evidence: confidence that the belief in question is more likely to be true than it is to be false. Lebens goes in this direction in his Guide for the Jewish Undecided by arguing that it would be crazy for someone who is already grounded in Judaism not to become religious if they become convinced that there is at least a 50% chance that God exists and, in addition to that, another 50% chance that God wants Jews to keep the Torah. Blaise Pascal famously made a similar argument, explaining that if one were to get to the 50% mark (even if not over that mark), practical considerations could then push the rest of the way. Christian apologist William Lane Craig summarizes it well in his book, Reasonable Faith

Pascal argues that since the odds are even, reason is not violated in making either choice; so reason cannot determine which bet to make. Therefore, the choice should be made pragmatically, in terms of maximizing one’s happiness. If one wagers that God exists and he does, one has gained eternal life and infinite happiness. If he does not exist, one has lost nothing. On the other hand, if one wagers that God does not exist and he does, then one has suffered infinite loss. If he does not in fact exist, then one has gained nothing. Hence, the only prudent choice is to believe that God exists. 

But what if someone engages in research and still ends up with less than 50% credence in religious propositions? Could such a person still justifiably believe them?  Protestant analytic philosopher Alvin Plantinga has noted that 

obviously you can’t have propositional evidence for everything you believe. Every train of arguments will have to start somewhere, and the ultimate premises from which it starts will not themselves be believed on the evidential basis of other propositions; they will have to be accepted in the basic way, that is, not on the evidential basis of other beliefs.

While John Locke argued that the only things one could take for certain in such a basic way are beliefs about their own mental state and self-evident facts, Plantinga argues that belief in God ought to be added to that list as long as it is warranted. In his words, “a belief has warrant for a person S only if that belief is produced in S by cognitive faculties functioning properly (subject to no dysfunction) in a cognitive environment that is appropriate for S’s kind of cognitive faculties, according to a design plan that is successfully aimed at truth.” Such a warrant does not show or demonstrate God’s existence, but Plantinga argues that should not count against it since relatively little in our own lives can be adequately shown or demonstrated when we really think about it. Indeed, Plantinga argues that belief in God ought to be “in the same boat as beliefs in other minds, the past, and perceptual objects.” All things being equal, such things do not require formal argumentation or propositional evidence in order to be believed in. In his words, “if my belief in other minds is rational, so is my belief in God. But obviously the former is rational; so, therefore, is the latter.”

Rational, Religious Conclusions

Whether arguments for God or experiences of God are truly warranted (such that they can be taken for granted even without propositional evidence) will be discussed in the next part of this series. For now, it should just be noted that if such a warrant can be aptly demonstrated, one might be rationally justified in taking belief in God for granted even in absence of overwhelming evidence.

Lebens goes in this direction as well, arguing that “as long as Judaism isn’t obviously false, [we] have overwhelmingly good reason to take the plunge on the chance that it’s true… the demands of rationality are such that we need lots more and lots better evidence for the falsehood of Judaism than we do for its truth – as long as we’re socially and culturally rooted in the way that many of us are.” 

Even if belief in God could be regarded as a basic belief for some people, and therefore require less propositional evidence; others may disagree. So while we will explore the question of belief in God as basic, this series will attempt to provide at least a preponderance (50% threshold) of evidence for the unbiased reader to take into account. The goal is not to prove anything beyond a shadow of a doubt, but rather to provide a rational and objective argument for Judaism from first principles that is in conversation with contemporary science and philosophy while not being entirely reliant on them. This will hopefully provide an explanation for many of Judaism’s beliefs that minimize explanatory gaps without creating more “gods of the gaps” in the process. 

Recommended Reading

The Big Picture: On the Origins of Life, Meaning, and the Universe Itself, by Sean Carroll

Sean Caroll’s complete worldview, including how one might think about the world through a pure Bayesian perspective.

Strauss, Spinoza, and Sinai: Orthodox Judaism and Modern Questions of Faith, edited by Jeffrey Bloom, Alec Goldstein, and Gil Student

Leo Strauss once argued that Orthodox Judaism is refuted by the philosophy of Baruch Spinoza only if Orthodoxy claims to know truth. If Orthodoxy only claims to believe, it can survive. This book records 15 Orthodox responses to Strauss’ claim.  

A Guide for the Jewish Undecided: A Philosopher makes the Case for Orthodox Judaism, by Samuel Lebel Philosopher Samuel Lebens’ argument for the rationality of living a religious life. 

Steven Gotlib is Director of Glebe Shul: The Capital Jewish Experience and Interim Rabbi at the Young Israel of Ottawa.



Each person approaches their religious values differently, and Rabbi Steven Gotlib gives us an insight into his own belief.


So does rationality offer consolation? The answer is of course that it depends—on what agonizes you and what sort of comfort you seek.


Without logic and reason, faith is bound to crumble. That’s exactly what happened to me.