Nothing is true until proven otherwise

One of the guidelines I try to follow is to strive to close the gap between my beliefs and the truth. That is, I want my mental representation of the world to be as close to reality as possible. This is a pursuit I find intrinsically worthwhile and is aligned with my desire to learn. But beyond the pure sweet taste of knowledge, striving for truth is also beneficial in practice. In fact, I find it hard to think of anything more useful. When I am about to cross the street, I look left and right to see if there are incoming vehicles. Knowing the situation I’m in is essential if I want to get to the other side without getting crushed by a truck.

A rule I’ve given myself that I try to follow as religiously as I can is: assume nothing is true until proven otherwise. What I mean is that I should avoid believing a statement unless there is good reason to do so. Skepticism, to put it in a word. A belief that rests on good reasons — i.e., a reasonable belief — is more likely to be accurate.

It isn’t always easy to hold such an approach, actually, it’s pretty hard, especially given the strong human tendency to believe what one wants to believe, but it at least sets a positive direction to follow.

Some may have noticed that the definition I gave of “reasonable belief” is a bit vague. When are reasons good? When can I say I have sufficient evidence to support what I think?

First, if I really want to be a jerk, I can doubt everything, fall into Solipsism, and go so far as to question the very fabric of reality. Following this path doesn’t seem useful to me, nor viable in practice. I may accept philosophically that I cannot be absolutely certain of anything, but I cannot act accordingly. I’m forced to assume that reality is real and to rest my thoughts and actions on a set of beliefs that I believe to be true (or at least accurate enough). I have no alternative.

Then, keeping in mind the pragmatic assumption that reality exists, I can decide how skeptical I want to be. In theory, this isn’t an actual choice either because there is a definite rule that states how I should update my level of confidence based on the information available to me: Bayes’ theorem. This theorem tells us, mathematically, how to revise the probabilities we assign to beliefs based on the evidence we have. As far as I know, it can’t get more accurate than that.

Unfortunately, resorting to Bayes in everyday life is impractical, bordering on impossible. Applying the theorem requires knowledge of the probabilities underlying the phenomena under consideration, probabilities that we almost never actually know. So the question remains, though slightly different: when I can’t apply Bayes’ rule, how do I know whether I have sufficient evidence? My answer is that one can resort to heuristics, which, while never exact, are still better than nothing. Some examples of questions I can ask myself:

• Is what I believe falsifiable? Is there, at least in theory, an observation that would force me to question it?
• Is the supporting evidence experimentally replicable? If I had the right knowledge and equipment, could I investigate that evidence?
• What does science say about this? Is there a theory that is supported by most of the scientific community? Are there conflicting theories? Is there an open debate?
• What is the source of the evidence? Has it proven to be consistently honest and reliable? Is it reasonably neutral or does it have a conflict of interest?
• Is the reasoning behind the belief rational? Have I checked for logical leaps and fallacies?
• Am I subject to some bias or prejudice that pushes me toward a certain position? Am I making unwarranted assumptions?

These and similar questions act as a checklist to quickly get an indication of how well-founded a belief is. On the other hand, for a more long-term-oriented approach, I find it useful to build a foundation in rationality, critical thinking, and the scientific method. And of course, when possible, studying the specific topic is still the strongest line of defense. The more knowledgeable you are about a subject, the easier it becomes to evaluate related claims.

An important “corollary” that follows, more or less, from all the above is the question of the burden of proof. I must avoid believing any assertion until proven otherwise, but who is responsible for bringing that proof? Simple: the person making the claim. Let us conduct a thought experiment to see why this is the case.

Let’s imagine that I am arguing with Pinky Ponky and he asserts X, where X can be any proposition, such as “this drink boosts the immune system,” “the earth is flat,” “god exists,” “there is a temperature of 28°C outside,” “ice is less dense than water,” “simultaneity is relative,” etc etc etc. To simplify the example let’s imagine X = “the core of the moon is entirely made of cheese.” To believe or not to believe? Let’s pretend that the burden of proof is not on Pinky Ponky but it’s my duty to refute the claim. According to these rules, assuming I have no evidence against it, I must believe that the moon has a cheesy core.

But now, when the discussion is about to close, Bean Bananean enters the scene. She has a strong opinion on the matter and wants to express it. Bean confidently says that the moon’s core is made of onions. As before, assuming I have no evidence against it, I have to give in and believe her. Since I cannot refute either of the claims, I am forced to agree with both. But how can I if the two statements contradict each other? I cannot; it is not logically possible.

Believing without evidence leads to contradictions of all kinds, since one can assert X and not-X just as easily. The burden of proof, therefore, is on who’s making the statement, and the most rational position, in the absence of good reasons, is to reject the belief.

Beware that this does not mean that I cannot choose to investigate by myself, nor that the person is necessarily wrong: even the opposite claim would have to be proven. It just means that I am entitled not to believe unless there is good reason and I have no duty to bring evidence against. “You cannot prove the opposite” is a direct violation of this principle and proves exactly nothing. It is a fallacious argument. Absence of proof is not proof of absence. Only those who do not have good reasons to offer use such a rhetorical device since, if they had any, they would bring those instead of trying to unload their duties on the interlocutor.

Keeping in mind where the burden of proof is located is important if I value truth. It nudges me towards minimizing the number of false beliefs I hold and helps me not to be fooled, especially by those who would profit from my naiveté: a sponsored influencer, the seller of a course on how to get rich, a politician looking for votes, the writer of a book on a miracle diet, an activist collecting donations. Maybe they are right, but not before they prove it. In the meantime, I reserve the right to exercise a healthy dose of skepticism.