How do people come to believe a thing? They can believe a thing because of reason, or take something on faith.
The realm of reason is systems of falsifiable facts, which is to say facts that can be shown to be true or false with certain levels of accuracy. Any person (or system!) that can reason and observe outcomes can come to agreement about a system of beliefs resting upon tested and falsifiable facts. One cannot have wars over the value of pi; the facts will speak for themselves.
Things taken on faith by definition cannot be proven. Critically, this means that they cannot be disproven. A foolish, if typical, defense of religion rests on this lack of disprovability, treating it as a strength and not a weakness. While it’s true that one cannot prove that God does not exist, there is an infinite set of absurd beliefs that also cannot be disproven; for example, that the world was created six seconds ago exactly as it is now with, of course, your memory of the past being invented by a metaphysical entity. If one were to believe all things that were non-disprovable, they would find many would contradict each other – and without a system for proving or disproving which beliefs to hold and which to discard, they’d have to hold all of these impossibly conflicting beliefs at the same time, or discard an arbitrary set of them.
Since articles of faith are not arrived at by reason, the path to emotional or spiritual belief differs from person to person and consequently is difficult to transfer via discourse or objective demonstration. Non-disprovable beliefs cannot be constructively argued — while acknowledging that history clearly demonstrates that the futility of the matter has not kept people from attempting to argue religion.
Emotional beliefs often transfer with passion – when we see someone deeply enthralled with an idea, that excitement can become infectious. Likewise, when someone who we admire believes certain things we tend to want to think like they think and believe what they believe regardless of rational inspection of their beliefs. This is why the role of the charismatic preacher is so often important to a fast-growing religion and also why parental indoctrination is so critical for these beliefs.
Much of this is an understandable shortcut; it would be impossibly exhausting to personally verify all of the facts that one believes, so there are some areas in which we have to rely on the reason of others. The degree to which I can share a system of reasoning with another is the degree to which I can trust a commonality of judgement and expectation. This commonality is the basis for systems of trade and standardization. I contrast the value of a house sold to me that a shaman insisted the gods would protect from collapse with a house sold to me inspected by a licensed civil engineer. It is possible that the shaman is right and that there are gods actually defending my house from harm, but unless I share the same set of beliefs it is difficult for me to accept…and impossible for me to verify.
It is difficult to measure the forward progress or development of religious beliefs. While we can certainly observe changes and schisms in movements, there is no clear bar by which we can say that these changes constitute improvements. Indeed, it is a very common thing for a longstanding religious movement to attempt to “return to its roots” and explicitly revert to an earlier belief system. It would be hard to argue clearly for or against such a reversion without a metric.
In contrast, falsifiable ideas can through experiment be observed to be true or false with varying degrees of certainty. Once a result is examined and agreed upon, future experiments strive for additional precision of certainty or to test new ideas. This allows for the intergenerational accumulation of a body of knowledge of ideas along with data from experiments that variously illustrate their truth. Every generation can then know more than the last.
Not infrequently, as we improve our precision of measurement, we discover that an idea that was thought to be verified is actually not entirely correct – it was merely sufficiently correct to be observed as such by a less precise experiment. Hence the value in re-running old experiments when new equipment or techniques can allow the experiment to be run with greater precision. This answers why scientists may dig into an experiment with such relish where they are expecting to observe a certain value (with greater precision) even when a few years ago an experiment to measure said value succeeded (with lower precision).
Skepticism is bred in the public when they observe as a consequence of the above that scientists seem to believe one thing (when an experiment is conducted that appears to show that a thing is true when observed at a certain level of accuracy) and then later not (when a further experiment measuring at greater detail observes a subtly but importantly different result). Without taking into account that the precision of the data measured is increasing, it can feel like scientists are vacillating, in the very same ways that religious movements can vacillate. This doesn’t look like progress.
But the difference is that models are discarded principally because they have been falsified; the falsified model will not be returned to later. It was discarded for a better model that, in turn, may be discarded but only when a superior model in turn arrives. As a species, our understanding of the universe advances and each generation is made more knowledgeable, powerful, and aware.
This process may never end because we know that measurement with perfect precision is an unattainable goal. Consequently every generation can only hope for superior precision to the last in testing our ideas. There are also not a finite number of ideas to be verified.
But what is the origin of these falsifiable ideas? How do we know what to test, and how? Some of these beliefs can be axiomatically built one upon the other, but many are arrived at through intuition, randomness, and/or accident. This means that half of science – the generation of hypotheses – is not itself arrived at through scientific process itself. It is held accountable to logic while not stemming from it.
Logic, therefore, is the course by which we may direct the spirit’s passions towards progress. With only reason, we would be able to observe and test but never discover new ways to observe or ideas to test. With only emotion, we would have many conflicting ideas and no way to advance. With both, in balance, we can continue to develop our species with new, better models of how the world works.