How Do You Know?
4th Jun 2020
Reading Time: 9 minutes
A common icebreaker between children and adults is to asking the kids their age. They rarely have trouble answering this question; it's a cornerstone of how adults relate to them, and they expect it. Although most children seem to have no trouble reciting their age when asked, they usually have a lot more trouble answering my follow-up question: "how do you know?"
Sometimes I just get a quizzical or skeptical look. Sometimes they call me "silly" or "weird". After all, it is a silly thing to ask, right? How old we are is such a familiar fact that it feels unquestionable. Even young children can recall it to mind with an ease that makes it feel like an a priori law of nature.
But we don't remember being born. Most of us cannot recall what life was like when we were only a year or two old, and remember little or nothing before the age of three or four, when our declarative memory fully develops. We haven't been counting the days since we were born, so we only know our age - and our birthday - because someone told us, and we believed them.
We come equipped with some powerful tools for understanding the world. Infants show signs of object permanence from as early as 3.5 months old. Object permanence is the ability to recognize physical objects and mentally keep track of their location and other properties, even when out of sight. Object permanence is the basis for many magic tricks - we tend to react when an object we are mentally tracking seems to disappear in violation of our normal understanding of how the world works.
Babies also come equipped with other skills that allow them to nagivate their world and acquire more knowledge, such as the ability to recognize individual faces, possibly even from birth, and an ability to acquire language. These innate skills serve as a our toolset for learning, rather than specific information about the world. Being able to recognize faces doesn't mean that a baby is born knowing who anyone is; being able to learn a language doesn't mean babies are born knowing one.
Children learn first by observation and by experience, reacting to things that happen to them. As they grow, they begin to learn by experimentation; trying things and seeing what happens. They learn by simulation, playing make-believe games where they take on various different roles and exploring fictional scenarios. They learn by interaction with others, developing social skills and processing assertions and propositions provided to them through language.
Knowing their age comes mostly through this final vector. Adults they trust, such as their parents, grandparents, and siblings communicate their age and birthdate to them as matters of fact from the moment they can understand language. They may receive corroborating evidence from interaction with their peers, observing that children who claim to be near in age to them are also at similar levels of physical and emotional maturity. Most children are probably never exposed to wildly contradictory information about their age as they grow up, and so find it simple to accept what they are told as an established fact beyond any need of doubt.
As children get older, they are also exposed to supporting documentation, like birth certificates, which serve to corroborate the testimony of their family that they were born on a certain day. Birthdates are very important in our society; they're often used as a proxy for quantifying "normal" physical and mental development. Pediatricians, preschools, and peers all ask a child their age. They see their parents using birthdates as a form of identification by government agencies and corporations. A child could be forgiven for believing that a person's age is an integral, immutable fact about them.
If you were to ask the vast majority of people living in any modern, industrialized nation if they knew their birthdate, they would. We think of a birthdate as a fact - a piece of primary, indisputable evidence about a person upon which other conclusions can be based. What could be more factual, more quantified, about a person than the date of their birth?
And yet, a human's birthdate is not something that can be objectively determined after the fact. If birthdates were not considered terribly important, as was common in pre-modern times and in many illiterate societies today, it might be very difficult to discover a person's exact birthdate. For many important historical figures, we have only approximate birthdates, based on christening dates or other circumstantial evidence. Birthdays are a distinctly modern invention of literate, numerate societies.
Humans don't have any physiological evidence in their bodies of their exact birthdate, the way trees have tree rings that correspond to each season's growth. Doctors and forensic investigators can estimate the age of a person based on typical parameters previously observed in humans, but this is never exact. Certainly never precise enough to identify an exact date of birth.
Besides, what exactly constitutes "birth"? If you've ever been present for a birth (besides your own), one aspect of it you will likely remember is that it was not an instantaneous event. There is a period of time during which a baby is unborn; that is, still completely inside its mother and utterly dependent upon her body for its survival. There is also a definite time when the baby has been born; when it is completely separated from its mother and able to survive independently of her body. The time in-between these two extremes might be summarized as the time when they were being born. But at what point - what precise moment - does a child transition from the state of unborn to born?
No matter how we define the moment of birth, the more important point is that we define it. The instant of birth is not an objective phenomenon in nature; it is an inter-subjective decision by people. In a society which values specific birthdates and times, some date and time must be recorded on the birth certificate and told to relatives. Without an objective criterion to fall back on, considerable discretion is left to the adults at hand - physicians, parents, nurses, midwives, friends and family.
Perhaps the date and time is recorded after the whole birth process is over, and that's considered "good enough". Perhaps the time is rounded off a little; perhaps it is guesstimated a little. Perhaps a baby born near midnight is given one date or the other, based on the parents' preference. Perhaps the recorder of the date could be cajoled into recording another, nearby date of significance to the family. Perhaps the person writing the birth certificate makes a mistake in the date or time, and no one thinks it important to correct it. Since the date and time of birth cannot be objectively verified after the fact, nothing prevents an inaccurate date or time from being recorded.
But once that date is recorded, it becomes the canonical fact. It is memorized by the participants, repeated to the child ad nauseum as they grow up, and requested incessantly by record-keepers as they grow into adulthood. That arbitrarily chosen date and time becomes the truth, enshrined as fact.
If an adult were to somehow discover late in their life that their birthdate and time had been falsified - perhaps via the deathbed confession of an elderly parent - and that their true age differed from what they'd always believed by a matter of minutes, hours, or even a day or two, most would probably not be overly troubled. Perhaps devout believers in astrology would be distraught at the news, but it's probably fair to say that most adults would find this imprecision to be a mild curiosity at most.
But suppose this person, for whatever reason, really wanted to have their birthdate officially corrected. What evidence could they possibly provide to convince an impartial curator of records that the revised date and time were more correct than what was originally written? If all the available written records agreed on a certain date, it would probably be nearly impossible to convince anyone that date was wrong. What stronger, more convincing evidence than the birth certificate could be presented to show that the recorded dates were wrong?
For all intents and purposes, the birthday that every person and written record agrees on for a person is their birthday. It is a fact, one that has been created entirely by mutual agreement of the people involved. It is not an Objective fact, but it is an Inter-subjective one. If everyone everywhere spontaneously decided that your birthdate were different, then it would be, and the records would be amended to reflect this. For example, say your country decided to adopt a different calendar and apply it retroactively to all birth records; your birthdate might change, and the new value would be the correct one.
Note that I said everyone would have to decide to make such a change. The Inter-subjective reality is co-constructed by all its participants, so changing something in it means having the agreement of all of the individuals involved, which may not be so easy. Once a fact has been established, other subjective and Inter-subjective facts get built around it, creating a logically consistent and inter-dependent web of knowledge.
Changing one fact - and getting everyone to agree to that change - could require changing many other facts as well, in order to maintain that consistency. The same pattern-recognition hardware our brains deploy to make sense of the external, objective world are put to use evaluating claims about Inter-subjective facts and how each fits with the other facts we've already accepted.
In 2018, a Dutchman named Emile Ratelband asked a district court in Arnhem to adjust his age by 20 years. The court refused, but what's interesting from an epistemological point of view is that all parties involved accept the court's power to make such a change. If the full power and credit of the Dutch government were put behind a different age for Mr. Ratelband, most people would treat the new birthdate as legally correct to avoid conflict with the Dutch government. They might lose some faith in that government, and few people would agree that he was in fact twenty years younger. Doing so would conflict with many other facts.
Whenever we encounter a new assertion and evaluate how likely it is to be true, we compare it to the facts we already know and see how well it fits with them. If a claim fits very well with what we already believe about the world, we judge it more likely to be true. The more an assertion disagrees with what we already believe, the more evidence we will need to convince us, because each contradiction created by the new information must be addressed and explained.
For example, adjusting a birthdate by a few hours or days with the explanation that new information has come to light about the birth is something people can understand, and the change has minimal impact on the logical consistency of the world. Adjusting a birthdate by twenty years would require much more adjustment. As the Dutch court observed, it would require editing twenty years of other records - the physical evidence supporting the logical consistency of our Inter-subjective reality.
At the heart of George Orwell's dystopian classic 1984 is the epistemic horror of an absolutist regime that compels its citizens to continually alter their knowledge of the past. A vast bureaucracy - The Ministry of Truth - is tasked with altering the physical evidence of the past, while Party members are compelled to consciously revise their memories using Doublethink, "the power of holding two contradictory beliefs in one’s mind simultaneously, and accepting both of them."
The epistemology of the Party is described:
The mutability of the past is the central tenet of Ingsoc. Past events, it is argued, have no objective existence, but survive only in written records and in human memories. The past is whatever the records and the memories agree upon. And since the Party is in full control of all records and in equally full control of the minds of its members, it follows that the past is whatever the Party chooses to make it.
In other words, the Party does not completely abandon logical consistency, but instead puts great effort into continually revising all evidence that contradicts whatever history is useful to them at the moment. If Inter-subjective facts are merely the product of agreement between the individuals involved, could this actually work?
One major obstacle to the Party's approach is cognitive dissonance. Doublethink requires effort, because we must constantly reconcile the contradictory information. We feel psychological pressure to resolve the conflict and settle on a single, coherent reality, and unfortunately for the Party, people's memories don't change without a fight. Whether or not the past has an objective existence, past events have left their marks on physical objects - including us.
Our minds and our memories are the product of our brains, and our brains are physical objects with a specific history. Events cause physical changes to our brains which are then incorporated into our mental lives. Our ancestors' brains were never under any evolutionary pressure to spend energy maintaining multiple realities or editing memories. Quite the contrary, life in the wild favors creatures that remember experiences accurately and construct models of the physical world that are consistent with those experiences.
If the Party of Orwell's nightmare were able to replace their citizens' brains with artificial ones, they would no doubt make it possible to simply erase old memories and replace them with new ones, as we can do on a computer. But their 1984 hasn't even heard of digital computers, so they're stuck working with squishy brains that cling tenaciously to memories.
The Party of 1984 would ultimately be foiled for the same reason a child refuses to reconsider their birthdate. Even though birthdates are completely arbitrary, the product of human invention and contrivance, the child is equipped with a sophisticated brain that remembers the past, prefers consistency over effort, and recognizes patterns. They may only know their birthdate because someone told it to them, but because it's consistent with everything else, they're right to believe it. It is a fact.