Assessing the Probability of Truth

It is time we revisit the fundamentals of how we reason what is true or false

We all disagree. On a lot of stuff. Politics. Religion. Which tastes better Italian or Thai food? Clearly the vast majority of what we take to be “true” is subjective. Then, why do we so often share our opinions in the form of absolutes?

I want to share a perspective I learned about recently called Bayesian reasoning. I will spare the reader the detailed history of its origins in science and get right to the meat of what it is and how you can and should apply it to virtually every aspect of your life:

Bayesian reasoning is the application of probability theory to what you hear and mentally digest. This is my definition, not Wikipedia’s.

The essence of it goes like this. In general, someone tells you a good idea – maybe you hear a political pundit on TV make what seems to be a reasonably sound point – and the usual thing people will do is say “that sounds right… it’s true” or “that sounds wrong… it’s false.” What Bayesian reasoning says is that you say to every possibility “Maybe it’s true, maybe it’s false.” Thus, I will assign a probability to it being true or false. Then I will go collect data and ask “What would the world be like if this were true?”

Let’s be clear, this principle should apply to everything from going through your everyday life and in personal relationships to being an actual professional scientist. Outside of things like gravity or the sun coming up, there isn’t much truly objective truth out there. So, look, go read a Deepak Chopra book, or watch Fox or MSNBC, and if you are tempted to believe what you read or hear on tv, then test it. Figure out, if X were true then the following things would happen…

If we all thought and reasoned more this way, perhaps, just perhaps, we might have more meaningful discourse and get more done.

To put this into context, if I were to tell you that the sun will come up tomorrow or that gravity will operate in the same way as it did today, based on your knowledge and experience, you assess the probability of that to be 99.99999…% true. I mean, of course, the sun will come up and gravity will work tomorrow, but you can’t actually know that. So, if I tell you that “Capitalism is the best economic system in the world” or that “Democratic Socialism is the next step in the historical evolution of effective governance” or that “hey, I think that pretty woman over there likes you;” rather than wholeheartedly accepting or outright dismissing any of those points of view as true or false, perhaps it is more productive, more beneficial, to assign a probability of truth to either statement and test it out. If we all thought and reasoned more this way, perhaps, just perhaps, we might have more meaningful discourse and get more done. I don’t know though. What probability of truth do you give that idea?


Mark Reid
Mark Reid
Mark Reid is the host of the Zen Sammich podcast. Previously, he was an English professor at Kanagawa University, Tokyo University of Science, and Ritsumeikan Asia Pacific University. He was also an attorney for 10 years, first as an Assistant District Attorney in New York state, and later worked in Securities Law for a large firm in Birmingham, Alabama. He now lives in the countryside of Japan and makes washi (traditional Japanese paper) for a living with his wife, Haruka. A graduate of the University of Alabama in political science and religion, with an MA from Florida State University in philosophy and ethics, and a JD from Syracuse University College of Law, he has a diversified background that through diligence and good fortune has taken him all over the world, including residential stints in Greece, England, and South Korea.

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  1. The “true” and “false” exist in particular circumstances. Relativism can only be applied in certain fields, when a factor is perceived differently by each individual; when it is not possible to speak of “absolute truth”; when our feelings are involved and, moreover, when no one is touched by our choices.

  2. Hi, Mark Reid.
    A good and TIMELY article. Thank you for posting it.

    To be able to truly assess whether or not something is ‘truth’, we probably need to define truth. The best definition that I have heard to date is this one:

    “A truth is something that NEVER changes.”

    Under that definition, even a lot of science can’t really be called ‘truth’ because new and ongoing research and discoveries keep changing the scientific landscape.

    Maybe maths???????????????

    And then you have to contend with individual perceptions, which can vary from where a person was standing when they witnessed the event to the mood they were in when they heard about it to past experiences in life all the way through to their political ideologies and/or religious beliefs.

    After which there are individual abilities for critical thinking, analysis, reasoning and logic – no wonder there are so many ‘versions’ of the truth of so many things.

    Way back when, when journalists still tried to TELL us the news instead of ‘manufacturing’ it, there was a WIDELY reported story that a man named Armstrong had ‘ackshully’ walked on the moon – – – – and there are still people who don’t accept that.

    Wunsa ponna time, everybody and their dog believed that the world was flat. Then some heretic named Columbus FAILED to sail over the edge of it – – – – and there are still people who will try to tell you that the world is flat.

    There are NONE so blind as those who will not see.

    Just my 0.02. Thanks again.

    You have a wonderful day. Best wishes. Deas Plant.

    • Again, I think you nailed it. Namely, that more often than not there are merely “versions” of the truth (which might all have some validity or rationale) rather than there being one capital “T” – Truth. And in some instances, sadly, some people refuse to accept any other truth than the one they staunchly believe in.

  3. Hi, Folks.
    Firstly, thank you, Mark Reid, for an interesting AND timely article. Good stuff.

    Next, I would suggest that before you can assess whether ANYTHING is ‘truth’ or not, you would first need a definition of ‘truth’. With that in mind, I offer you this one:

    “A truth is something that NEVER changes.”

    By that standard, there are VERY few real truths in the world or in any of our lives. Even much of science and medicine can NOT be said to be truth because they often change with new research and findings.

    As for the news, even way back when, when journalists were trying to REPORT the news instead of ‘making’ it, there was always the possibility of some bias creeping in or even just a viewpoint – which could be as innocent as which side of the street they were standing on when they witnessed an event – – – or as manipulative as a political agenda.

    All I try to is to assess for myself the logic and reason of what I read and/or hear and, to some extent at least, assess the source or sources from whence it came and base my level of acceptance on those things. All of these assessments can at best be subjective unless I was a witness to or a participant in the related events.

    I also try to be NON-judgemental when it come to the ‘ rights’ or the ‘wrongs’ of what people do and/or say as I believe in freedom of expression. Instead, I ask myself if that is something that I would like to read in my autobiography and base my future speech and actions on the answer to that question.

    Another way of putting this is: “It doesn’t matter who else you sleep with, you still have to sleep with yourself.”

    Just my 0.02. Thanks again, Mark Reid.

    You all have a wonderful day. Best wishes. Deas Plant.

    • Thanks for your insight, Deas. I agree there are very few real truths by the definition you posited and that bias creeps into our observation, even by way of “which side of the street” we are standing on when we observe something. I assess the validity of your statements to be about 87% true (that’s a joke).

  4. Good post, Mark. I try to put any idea to the “smell test”. If it doesn’t “smell right” then I have doubts about it. I also try to find the source. Having found the source, I explore what the potential/probable motives are for presenting the idea or position. Those processes usually lead me down a path that I am comfortable in believing or trashing. Welcome to our little corner of the world.

  5. Welcome Mark and congratulations on a powerful and thought provoking essay!
    The concepts here on probability theory are brilliant.
    “If we all thought and reasoned more this way, perhaps, just perhaps, we might have more meaningful discourse and get more done.”
    The answer is YES. #BRAVO

  6. Hi Mark, welcome to the tribe. That was a very interesting and well reasoned post or maybe it wasn’t. No just kidding. The hard part of having a disciplined methodology for discerning what’s real and what’s not, I would argue, could very well be beyond the intellectual capability of the people who would need it most. For example, can you see someone carrying a sign in serious need of spellchecking and grammar checking read this article and actually have a light bulb go of in their head? Don’t get me wrong, I think it’ s a great methodology for people who can actually embrace both sides of any issue. But, IMHO, the people who really need to do this are the very ones who don’t seem to be able to. It would be great if there was a way to mix this into their coffee and have it manifest in their consciousness. Who knows, maybe there are a bunch of mad scientists working on just such a thing as we speak.

    • Yeah, unfortunately, I think you are right that many people simply aren’t capable of this kind of reasoning. It might not be their fault even. We are hard wired for survival, right? To think fast and decide “this is true” or “this is right.” But, one of the benefits of being an “evolved” species is that we can have these conversations in the first place. And, I do feel that with the world becoming increasingly polarized, we have to stress the importance of critical analysis over simply buying into whatever a political party or a particular religious leader simply tells you to believe.

  7. Mark: Bayesian reasoning certainly sounds worth a try, and likely much more productive than Googlesian reasoning! Some of what we collectively believe can, of course, be argued ad nauseam. We can split hairs all day long, for example, around your contention that ‘the sun comes up every morning.’ Of course the sun doesn’t move at all, but our perception has it ‘coming up,’ so it’s often simple semantics. I believe part of our contentiousness these days has to do with knowing too little about too much. Just my 2 cents. Thanks for writing.

    • Excellent point, Byron! I think that’s really what I was trying to get at, that so many people speak in absolutes while not realizing that they are speaking from a point of relativity (e.g., as you pointed out, that the sun doesn’t “come up” at all… you just see it that way from where you are standing). I think MOST of our “truths” are only true from a particular point of relativity. Thanks for your input.

    • Can’t help but pointing out that the sun actually moves because the whole galaxy does, but from our point in the same solar system, it stands still. Ha, just splitting hairs because I can.

      That said, Mark, I love this piece and how your comment back to Byron lifted perspective elegantly into the conversation. Is it a 6 or a 9? Yes.