The "Reasonable Certainty" Standard for Belief
(Re)solving the problem of other minds, our duties to future people, and believing in the unknown
TL;DR: When is it unreasonable to be skeptical? When available evidence shows that a conclusion is intuitively certain and any doubt is only resolvable with evidence that is impossible to obtain.
Since all available evidence shows that other humans have minds like our own, we can be reasonably certain of other minds. Doubting other minds is, therefore, unreasonable if it requires impossible evidence to alleviate. The same principle of reasonable certainly also creates moral concern for future people as well, who we can be reasonably certain to exist in our future. Not being able to see into the future isn’t a valid basis for denying the moral standing of these future people. And reasonable certainty can also let us reject other ideas, like the existence of god and aliens.
Imagine a murder trial. The prosecution presents overwhelming evidence that a defendant had shot and killed a victim. The defendant was shown to have a violent history and was on bad terms with the victim. Witnesses testify that they saw the defendant carry out the shooting. When in custody, the defendant had no alibi and confessed to the murder shortly after some police interrogation. The defendant was also found in possession of a gun, which ballistic evidence verified to have been the murder weapon.
However, the judge refuses to convict the defendant. Why? Because the judge personally did not see the murder. “How can I take someone else’s freedom away when I can’t be absolutely sure he was responsible for the crime?” he asks sincerely.
You might think the judge has a prejudicial soft spot for the victim and isn’t fit to sit on the trial. Or the judge might be an overly skeptical philosopher and isn’t fit to be a judge.
Yet the judge might be right. If you’ve seen 12 angry men, you know that any “reasonable doubt” is enough to let a defendant go, despite overwhelming evidence to the contrary. In the above case, the defendant may be getting framed, and the police might have only elicited a false confession. If we can’t be truly sure, then what’s the justification for taking someone’s freedom away? As will be discussed below, the keyword in “reasonable doubt” is “reasonable.”
According to nearly everyone, the judge above is either corrupt or confused. Yet, according to some philosophers, the judge is only exercising sensible skepticism, which can be necessary when another’s rights are on the line. If a decision gets made in the above murder case, it’s because of practicality rather than principle.
It’s not enough to be 95% certain. Some philosophers may argue that without 100% certainty, our beliefs are not sufficiently justified. We might have to suspend judgment entirely if we lack a firm basis from which to make this judgment. One notable example of this skepticism is the problem of other minds.
The Problem of Other Minds
You might know that you’re conscious in the same way that I know I’m conscious. Yet how can you know that I’m conscious, and how can I know that you’re conscious? We may be certain that we are currently experiencing consciousness, but this is truly the only phenomenon we can be certain about. Therefore, anything beyond our own subjective experience is subject to suspicion.
And if we can’t be sure that others are free, conscious beings, then why be moral? We might be in a video game, and all those lives that you think are moral agents are nothing more than computer-generated pixels. Killing them would be as immoral as killing nazi zombies in Call of Duty.
Philosophers believe the problem of other minds to be an irresolvable dilemma, at least until we can transfer our consciousness and develop certainty for ourselves.
Other beings may behave the same us and are wired the same as us. And there is no evidence to deny that their internal states are any different from our own. But can we be sure they really are like us?
Yet we should respond to this skepticism. To what extent is this supposed problem of other minds reasonable?
The Reasonable Certainty Principle
There is something rationalists love about doubting. Skepticism is viewed by many as the hallmark of reason. No matter something’s internal logic or explanatory power, every scientific theory is subject to falsification and should be challenged.
Yet skepticism isn’t reason itself—it must be grounded on reason to be justified. And there is reasonable and unreasonable skepticism. The former is justified and helps us advance our knowledge. The latter is either unproductive and has us going around in circles or causes us to suspend judgment to the point of counterproductive ridiculousness.
The only authority over free people is reason. And for skepticism to be reasonable, it should be justifiable to others. Therefore, if skepticism isn’t justifiable to others, it lacks authority over free people (and can be freely ignored).
And what makes skepticism justifiable or unjustifiable to others depends on whether we have what I will refer to as “reasonable certainty.”
Reasonable certainty is when all available evidence leads to a certain conclusion, sufficient to justify that conclusion on intuition,1 and the remaining doubt can only be resolved with evidence that is impossible to obtain.
It is"certain” because we would intuitively act as if we were certain, based on all available evidence. And it is “reasonable” because having doubt that can only be alleviated with impossible-to-obtain evidence is unreasonable. Yet if we have doubt based on evidence that can be obtained, our doubt remains reasonable.
Given our conclusive intuitions, we can be reasonably certain that billiard balls will move when they are hit. Lacking perfect foresight isn’t a reasonable justification to deny our intuitive conclusion.
In the above murder case, the judge must find the defendant guilty since all the available evidence leads us to intuitively conclude that he committed the crime. Time travel is the only way to obtain the evidence required to cure the judge’s doubt (allowing him to watch the defendant commit the crime), which is unreasonable.
And the same applies to the so-called problem of other minds. We can analogize from ourselves that people built and behave like us also have minds like us, and are therefore free.
It wouldn’t be parsimonious if we shared the same internal features as others, expressed the same behaviors resulting from the same stimulus as others, yet had an entirely different conscious experience from others. Is it even conceivable to think those parallel mechanisms that produced parallel results were the result of different, yet immeasurable, operations? Is it reasonable to believe in some shadow universe that creates philosophical zombies among materially-similar beings?2
Denying the freedom of others isn’t reasonable. It’s not because of “practicability” that we obey moral rules, but because we submit our will to reason, which informs us when skepticism is and is not warranted. This is why we accept the freedom of the other parties in the social contract.
The “reasonable certainty” standard also means that the more evidence that becomes possible to obtain (say, through better technology), the more reasonable our doubt can be. So if we can get 100% certainty, despite having only 99%, it’s appropriate to want to pursue that 1%.
For instance, we don’t deny the insanity defense simply because we can’t experience someone else's subjective experience for confirmation. Yet as we learn more about the workings of the mind, the standards that are required for making this defense should change equivalently. If we can be more certain that someone was acting from a mental deficiency (say, through certain brain patterns), it’s reasonable to be skeptical if evidence of a mental deficiency falls below that standard (say, relying on only witness accounts).
Yet it’s not reasonable to deny the defense because we cannot transfer our consciousness. That standard is impossible to meet and therefore is unreasonable.
Duties to Future People
I’ve argued elsewhere that we have duties to free, existing beings—not fictions. Hypothetical people exist outside our moral universe, and we consequently don’t have duties toward them. Childlessness and murder may both lead to the non-existence of a being, yet both are not equal moral acts.
Yet this doesn’t mean we can churn through all of our natural resources and pass on overwhelming debt to the next generation. We may not be certain that there will be people in 2122, yet we are reasonably certain that there will be.
Just like how generations have procreated and persisted in the past, we have no reasonable basis to doubt that generations won’t continue to do so in the future. And these people who are reasonably certain to exist in the future are also within our moral community, being parties to the social contract.
Any contractual agreement made behind a veil of ignorance would include people of different generations. And using the time period we live to horde resources for ourselves and deny them to the “reasonably certain to exist” future people, is an exercise of power, not reason.
Under the agreement between parties, we wouldn’t place burdens on the current generations to save the nonillions of future generations. Yet our current generation isn’t free and clear of duties to future people either.
More likely, the social contract would include a Rawlsian Just Savings Principle where all generations would agree to a certain amount of conservation and accumulation. Not an overwhelming burden, but still giving fair consideration for future well-being.
We wouldn’t require Dark Age peasants to act on behalf of our 21st-century welfare. And we 21st-century humans aren’t required to act on behalf of 31st-century transhuman welfare.
God, Aliens, and Other Dogs That Don’t Bark
The reasonable certainty principle doesn’t just help us accept certain conclusions but lets us deny them as well.
Evidence of god and aliens are possible if they exist. If an all-powerful being or hyper-advanced civilization were to exist, it would have left its mark on the world in some way. If these beings are so almighty or intelligent, then why would they be so shy?
Mere proof of their existence is a very low standard. It’s not impossible to find cases of clear divine intervention or obvious UFOs (no, not just shadows). Yet, since no such evidence exists, we can reasonably conclude that these beings also don’t exist.
Or let’s say that these beings are so powerful that they can hide all evidence of their existence to remain hidden for reasons beyond our comprehension. In that case, any evidence would be impossible to obtain, and we can still reasonably conclude that they don’t exist.
Moreover, many who say these beings exist don’t actually act as if they exist. They don’t live their lives as if the evidence was intuitively conclusive. Rather, people who tend to believe in god or aliens, or any other supernatural entities, act a lot like non-believers. Wouldn’t believing in something as world-changing as god or aliens at least change your own internal world?
The primary difference between believers and skeptics is how much believers talk about believing something. Yet talk is cheap. And talking might only be intended to convey how one desires to be perceived rather than wanting to present a truly convincing argument. Too often, believers in gods or aliens want to believe and want the world to know that they believe, rather than act as if they believe.
Skepticism is fine, but it must be justified by reasons others can accept. If our only source of doubt is only resolvable by impossible-to-obtain evidence, then it’s unreasonable to concern ourselves over it. Instead, we should let the existing and possible evidence determine what’s justified to believe in, not the impossible evidence.
We don’t acquit people because of our 1% doubt that can only be resolved through omnipotence. We don’t kill others on our belief that they’re videogame pixels because we can’t experience their consciousness. We don’t screw over the next generation because we can’t see into the future. Instead, we act on what is sufficiently convincing and don’t demand the ridiculous when making decisions.
We need a principled way to settle our disagreements. Too many self-satisfied skeptics feel free to doubt the world only to act like everyone else due to “practicality.” Yet let’s call practicality what it is—reasonableness, and ungrounded skepticism what it is—unreasonableness.
Meaning that we would live our lives as if that conclusion was certain, given all the available evidence.
See “Why Materialism Is Baloney: How True Skeptics Know There Is No Death and Fathom Answers to life, the Universe, and Everything” by Bernardo Kastrup for a more in-depth discussion.