An Improbable Definition of Faith


Today’s problematic definition of ‘faith’ comes from Loftus, himself, as he expands his description of faith as “an irrational leap over the probabilities.”  While emailing a Christian friend, he offered the following definition:

In my opinion faith is what fills in the gaps of the probabilities. If, say there is a 70 % probability something is the case then to conclude more than that 70% probability is faith, and I reject faith based reasoning like that. To reject that kind of faith is to live and operate based on the probabilities. If there is a 70 % chance of something then that’s all I can conclude and that’s all I can use to base my decisions on. And so I could never give my whole life over to a 70% probability. I could only give 70% of my life over to a 70% probability. This is Lessing’s ditch when applied to the past, as you know. Kierkegaard responded by acknowledging Lessing’s point and therefore decided faith must go beyond what the evidence calls for. And that’s what I must reject.

Loftus’s Christian interlocutor replied that he thought the phrase “faith is what fills in the gaps of the probabilities” was spot-on and a great way to encapsulate Hebrews 11:1.  I can’t speak to the exegesis, but I sure as heck have an issue with this treatment of probability.

Loftus is essentially saying that, when we aren’t certain, we have to hedge our bets, but that can be the wrong way to reason.  Let me give an example.  I tell you that I have a weighted coin — it is 60% likely to come down heads and 40% likely to come down tails.  Plenty of people, given this data, will conclude that they should call out ‘heads!’ 60% of the time and ‘tails!’ 40% of the time.  They’ll lose out to the people who call ‘heads!’ every single time you play with enough iterations.

If you’re doing a math test, you’re going to mark down a lot of probabilities that aren’t zero or one, but, when you’re taking action, you pick the best option you know of and commit to it.  It doesn’t matter that you think there’s a only a 70% chance that you’re right, instead of a 99%.  If you think it’s the best choice, you’re only self-sabotaging by hedging.

What that 70% means is that you need less new evidence to change your mind about this action than you would if you were truly 99% confident.  But, absent that new evidence, there’s no reason you shouldn’t stay the course.  Instead of half-heartedly committing to the choice you’ve made, you should just stay vigilant that you don’t discount new evidence in either direction, because you’ve started thinking of your current confidence level as an important part of your identity, one that it would hurt you to lose.

I’ve been framing this in terms of choosing actions, but it goes for beliefs also.  The main difference here is that there’s less obviously a moment of ‘choosing.’  When your estimate hits some critical level, you believe.  You can’t change your belief by an act of will, or a “jump over the probabilities.”  You can only change what you profess to believe, so that you don’t feel like you’re betraying the side.  But check out the link in the previous sentence to see how different belief looks from belief-in-belief.


*I’d like to preempt one objection I think may come up in the comments.  People are going to ask some variant on the Abraham question: “What if I’m very confident that the right thing to do is the wrong thing?”  I think you’re describing your reasoning incorrectly.  The choice that’s before you isn’t sundered from all the other data/priors you have; a good Bayesian is factoring them in.  Those qualms (or, more precisely, the evidence that causes your qualms to trigger) count as evidence against the choice that scares you.

About Leah Libresco


  • http://last-conformer.net/ Gilbert

    I don’t think this disagreement tracks the Christianity/atheism-devide, but I’ll take this opportunity to mention I reject your entire epistemology.

    Probabilities live on probability spaces and are meaningless without those probability spaces specified at least implicitly. Assigning probabilities to all our beliefs doesn’t make sense because we don’t even know the sample space. And in fact we don’t do that. Our beliefs just aren’t real numbers. Now some people cling to platonic idealizations of themselves whose beliefs would be real numbers (“perfect Bayesians”), but I have no need of that hypothesis. In reality “X% sure” is most of the time a figure of speech and not a mathematical statement. And that is good.

    On a more practical level, beliefs are mostly not changeable by single acts of the will, but eventually masks tend to shrink on and biases are heavily influenced by what we wish to believe. In the long run that makes beliefs much more voluntary than most people’s self-image would admit them to be.

    And while we’re at comforting pop-psychological explanations of disagreement, you only talk about this “belief in belief” thing because you’re angry at God.

    • http://deusdiapente.blogspot.com J. Quinton

      No one is saying that you have to have exact probabilities to think like a Bayesian, you just have to be aware that all events have multiple explanations, and some explanations are more likely than others given approximate probabilities. For example, the phrase “extraordinary claims require extraordinary evidence” makes perfect sense if you think in terms of Bayes theorem; anyone who follows that advice is a Bayesian to some degree. Yet, how do you figure out what “extraordinary” means? You would have to have some ballpark “low probability” figure.

      You might say that Leah is “angry at god” but, if you thought like a Bayesian, you would at least attempt to look at the multitude of reasons for why she writes what she does and not stick with the “angry at god” reason.

      • http://last-conformer.net Gilbert

        I have nothing against the Rev. T. Bayes’ theorem. It is a useful calculation tool for probability spaces. I just object to using it as a universal hammer turning everything into nails shaped like probability measures. And my main objection is not the faux precision, bad as that is, but the blotting over of the issue of the undefined sample space.

        Being aware that “all events have multiple explanations” has absolutely nothing to do with statistical ideologies and, unless you misunderstand “likely” in too technical a way (which would be question begging) neither does awareness that “some explanations are more likely than others”. The “given approximate probabilities” probably (haha) does count as thinking “like a Bayesian”, but I don’t see how that should be a good thing. The way real people actually think we don’t have even approximate probabilities for most of our beliefs and neither should we. Of course that needn’t hinder us from using probability as a figure of speech. But then it’s a figure of speech, not an approximation.

        “Extraordinary claims require extraordinary evidence” makes sense if we take “extraordinary claims” to mean “claims against which we already have substantial evidence”. In that case it reduces to “look at all the evidence”, something quite understandable without pseudo-mathematical voodoo. But in common practical usage it’s more of a rhetorical battle-cry than of a sound epistemological principle.

        As for the last paragraph the snark doesn’t quite seem to have carried through, so I will have to work on my unsubtlety.

  • deiseach

    “I could only give 70% of my life over to a 70% probability.”

    Given that this is the week of Cheltenham, has the man ever bet on a horse in his life? Even in the usual workplace sweepstakes where you join in not because you expect to win, but just for the craic?

    This Loftus bloke must be great fun at family gatherings and other social occasions.

    Suppose I am stuck on the top floor of my house, which is on fire. If I stay in the room, the best thing that will happen is that I will suffocate due to smoke inhalation (the worst thing is that I will be burned alive while conscious). However, if I jump out my window, there’s probably a 70% chance I’ll break at least one leg, maybe both.

    Is there anyone who would stick 70% of their body out the window and keep 30% inside? Or who would not jump out the window, even though they can’t be 100% sure they’ll walk away unhurt?

  • InvincibleIronyMan

    Ooh, nice! I’ve been folowing John’s posts on this subject, and this is by far the best objection I have seen to anything he’s said. I bet there are quite a few theists out there who are kicking themselves wishing that they had come up with this!

  • Patrick


    I can’t see why this would be so. Is this a psychological claim? Are you using “belief” to mean “certain enough that I treat the possibility of err as negligible?”

  • Jay

    Leah, you’re clearly correct on the point that it’s not always right to hedge our bets when faced with uncertainty, and depending on how literally to interpret Loftus’s comment about only giving 70% of his life over to something, that’s a valid criticism. For example, if I somehow thought there were a 70% of Catholicism being true on all counts, I sure as hell wouldn’t be a 70% Catholic — I’d be as close to a 100% Catholic as I could possibly be.

    But I think Loftus is still onto something when he says that faith (at least for many people) is something like jumping over the probabilities. You see this sentiment reflected in the phrase “but there’s still a chance, right?,” especially when religious people encounter scientific arguments for why their beliefs are so improbable. I don’t claim that “faith” is any one thing for all people, but for many, I expect that “faith” is the name given to the wordless process by which motivated believers accept certain propositions that, on some level, they know to be less likely than other alternatives. It’s a way of reducing cognitive dissonance — “I understand why you think this is unlikely, but there’s still a chance, and I have faith.”

    Indeed, one sort of argument you often hear put forward to defend Christianity is that it’s right precisely because it’s so improbable. That sort of argument is dangerously honest for people who want to go on believing, because it comes close to giving away the game entirely. And I don’t expect many believers would acknowledge my concept of faith as correct, because it would require admitting that it’s just a trick to reduce cognitive dissonance. But for a lot of people, I think that’s what this concept of “faith” is actually doing.

  • deiseach

    Let me just throw this freshly-hewed hunk of bleeding quotation onto the table:

    Science likewise is pluriform, each science having its own specific object and method. There is a modern tendency to reserve the term science to “hard” sciences (mathematics, experimental sciences, etc.) and to dismiss as irrational and mere opinion knowledge which does not correspond to the criteria of those sciences. This univocal view of science and of rationality is reductive and inadequate.”

    Three guesses where this comes from?

    From here, a report by the International Theological Commission, an advisory body to the Congregation for the Doctrine of the Faith (formerly known as the Roman Inquisition). There is also a long section midway through about faith, what it is, how it is found, and so forth, which may be of some bearing on the topic under discussion.

  • Tara S

    Ooo. Yes to all of that…all of these clever people!

    I especially like the “belief-in-belief” link. I used to be a “belief-in-belief” type of person (that silly creature also called The Ironic Christian), but I don’t make any excuses for the dragon in my garage anymore. Seriously, go look! A dragon!

  • http://prodigalnomore.wordpress.com The Ubiquitous

    Leah: Have you seen the right answer yet? Faith, being an act of the will, &c:

    To have faith, or to believe, is not simply to make a passive assessment as to the probability that something is true, it is to decide to believe something to be the case or not be the case (and one presumes to act accordingly.)

  • Pingback: “Ethics is Like Physics” is total me-linkbait

  • Darren

    I have to say “Nope” to the whole ‘missing 30%’ idea. I fail to see how this correlates to any use of the concept of Faith that I have seen.
    So, I shall try my own definition, quite possibly taken unwittingly from some unremembered source. Belief is a conclusion based upon insufficient evidence, Faith is a conviction in the face of countervailing evidence.
    Disagree? Let’s look at common articles of Faith within the Christian frame: humans die, remain dead for multiple days, then reanimate; humans walk upon the surface of water; virgins conceive; water transmogrifies into wine; humans are bitten by venomous snakes with no ill effects; frogs fall from the sky; shrubbery spontaneously combusts and engages in conversation with humans. Our common experience says that these things do not happen. Science says that these things cannot happen, not probably don’t, but cannot. So, how is one to Believe they do? By Faith.
    In my Youth for Christ days, a speaker told a story about Faith.
    A tightrope walker was demonstrating his skill by crossing a line strung between the near and far shore shores of Niagara falls. A crowd had gathered to watch as the man crossed the line to the far shore, then crossed back. Not content with his feat, the tightrope walker crossed again.
    Then he crossed a third time. Addressing the crowd, he asked the question, “Shall I cross again?”
    The crowd replied that he should. The walker then addressed one particular observer, “Do you believe I can cross again?”
    The observer answered “Yes.”
    Then the tightrope walker asked the man, “Do you believe that I could cross carrying a load upon my shoulders?”
    Again, the observer answered “Yes.”
    The tightrope walker returned to the man and asked, “Do you believe that I could cross carrying a man on my shoulders?”
    Still, the observer answered, “Yes.”
    Finally, the tightrope walker said proudly, “Very good! Climb on!”
    I was told that the members of the crowd had Belief, but that it would take Faith to climb onto the tightrope walker’s shoulders.
    This does not, however, correlate with how Faith is understood or promoted. The crowd knew of tightrope walkers. Even if they did not, they had just seen this one cross multiple times. They had never seen him do so carrying a man on his shoulders, but the task would not seem that very different. If the walker says he has done so in the past, and is confident he can do so again, we can be expected to Believe him. Climbing onto his back merely confirms our Belief, ups the confidence limit is you like, whether justified or not. Here is your ‘missing 30%’, but this is a far cry from resurrection or virginal conception.
    Imagine instead the tightrope walker standing before the crowd, explaining to them how an Angel of the Lord guided him to a secret cave wherein he found tablets of gold with mystical writing. The writing, being translated via the artifice of magical scrying stones, instructed the tightrope walker in the weaving of an infinitely strong, yet completely invisible rope. The tightrope walker than claims to have constructed such a rope, and to have secured it to the near and far shores. As proof of this, he will walk along the rope, and invites a member of the crowd to come along with him, held aloft on the walker’s shoulders.
    That would be Faith.
    Few proponents of Faith choose such obviously testable examples, though. It is more typical to have the Bert and Ernie scenario.
    Bert and Ernie are walking along. Ernie appears to have a banana lodged in one ear.
    Bert says, “Hey, Ernie.”
    No response.
    “Hey, Ernie.”
    No response.
    “Hey, Ernie!”
    Ernie pulls out the banana and answers, “Sorry Bert, you’ll have to speak up, I have a banana in my ear.”
    “I noticed.” replies Bert, “Why?”
    “To keep the Elephants away, of course.”
    “Ernie, you idiot, there aren’t any Elephants around here!”