How Do You Know You're Not Just Making It Up?
The Apple on the Table and the Big Question
Imagine you wake up on a school morning and see a bright red apple on the kitchen table. You immediately believe there’s an apple, and it’s red. Most of us would say your belief is justified—you have every right to hold it. But what exactly makes it justified?
For centuries, philosophers thought three pieces had to fall into place for you to know something: the belief must be true, you must actually believe it, and you must be justified in believing it. Justification is the special sauce—the good reasons or evidence that back up your belief. In 1963, Edmund Gettier (1927–2021) rattled this picture by showing that you could have a justified true belief that was really just a lucky accident. After that, the hunt was on for what justification itself really is.
Alvin Goldman’s Ground-Shaking Idea: Your Brain as a Factory
In 1979, Alvin Goldman (born 1938) turned the search upside down. He said justification isn’t about having good reasons you can recite on the spot. Instead, it’s about the reliable belief-forming process that produced the belief inside your head.
A reliable process is a mental factory that tends to crank out true beliefs way more often than false ones. Standard perception, clear memory, and careful reasoning are reliable. Wishful thinking, hasty guessing, and believing something just because it feels good are unreliable—they often lead you astray.
Goldman’s key move was to make justification a matter of mental history. You don’t need to be able to explain why your belief is reasonable right now. What matters is the actual track record of the brain machinery that caused it. If your perceptual system works well in the world—like a thermometer that usually gets the temperature right—then the beliefs it spits out are justified.
This idea was a huge break with the past. Older theories said justification depends only on what’s going on inside your consciousness at this very moment. Reliabilism says the reliability of the hidden process is what counts, even if you have no idea how it works.
The Clairvoyant Who Knew Too Much
Right away, other philosophers spotted a problem. Laurence BonJour (born 1943) asked us to imagine Norman, a perfectly reliable clairvoyant. Norman’s psychic power spits out true beliefs with fantastic accuracy. One day it tells him, without any images, sounds, or reasons, that the President is in New York City. Norman has absolutely no evidence that he has this power, or that it works. He just finds himself believing the claim.
Intuitively, Norman’s belief doesn’t seem justified—it feels like a lucky guess from the outside. But if reliabilism only cares about the process’s actual truth-ratio, Norman’s belief should count as perfectly justified. That seems to miss something important: justification seems to require some awareness or connection to evidence, not just a hidden reliable machine.
Some reliabilists reply by shifting the focus to how ordinary people actually judge justification. Called approved-list reliabilism, this version says we all build mental lists of processes we’ve learned are reliable or unreliable—like “vision” on the approved side and “wild hunches” on the disapproved side. When we meet a case like Norman’s, we file clairvoyance with suspicious, unproven powers, so we judge it unjustified. That’s why our intuitions push back, even if the process is, in fact, reliable.
The Evil Demon and the Virtual Reality Trap
Stewart Cohen (born 1957) and others crafted a second famous challenge: the new evil demon problem. Suppose a powerful demon feeds you a perfect virtual reality, exactly like the real world. Every apple you “see” is a fake, every voice a trick. The demon-world you has exactly the same sensory experiences as real-world you. But in that demon world, your perceptual processes are completely unreliable—they never lead to truth. According to simple reliabilism, your beliefs would be unjustified. Yet it feels wrong to say that you and your demon-world twin differ in justification when your inner lives are identical.
A clever reliabilist response distinguishes two ways to measure reliability. One way is reliability relative to the actual world. Another is reliability relative to the world the subject inhabits. From our perspective, the perceptual processes of the demon-world victim are unreliable relative to their own world. But they are reliable relative to our world, where perception normally works well. So we can allow that their beliefs are justified when we evaluate them using the standard of our world. This indexical reliabilism tries to keep the reliability intuition while saving the sense that the demon’s victim isn’t doing anything wrong internally.
Other philosophers take a harder line and deny that the demon-world person has justified beliefs at all. They might say that evidence is itself a matter of what you know, so the demon’s victim has less evidence than we do, making their beliefs excusable but not fully justified. This option still gives their beliefs a positive status—blamelessness—without calling them justified.
The Too-Many-Processes Problem
Perhaps the most stubborn puzzle is the generality problem. When you see a maple tree and believe “there’s a maple tree,” which process are we supposed to evaluate for reliability? Is it just “vision”? Or “vision on a sunny afternoon”? Or “recognizing leaf shapes”? Your belief is the result of a single token mental event, but it can be typed in countless ways, some highly reliable, some less so. There’s no obvious fact of the matter about which type is the right one.
One strategy is to look at how psychology actually carves up the mind. Some philosophers say the correct type is the broadest information-processing algorithm that is psychologically real and causally responsible for the belief. That narrows things down, but critics worry that multiple psychologically real algorithms still overlap. Another approach lands on common-sense typing: ask ordinary people how they would describe the belief-forming process. Experiments show that when shown scenes of people arriving at conclusions, people converge on mid-level labels like “hearing a story” rather than super-specific ones. If our everyday reliability judgments already track justification, maybe that folk typology solves the problem—or at least shows that the problem isn’t unique to reliabilism.
Why This Still Matters Every Time You Trust Your Eyes
Reliabilism changed how philosophers talk about trust in our own minds. You don’t need to be a tiny scientist inside your head, checking every reason before you act. The world can be deeply reliable even when you can’t prove it from the inside. That thought gives a foundation for ordinary life—for believing what you see, what you remember, and what careful reasoning tells you.
But it also leaves you with a responsibility. If justification depends on the real-world reliability of your mental processes, then wishful thinking, rumors, and quick emotional reactions are real dangers. Part of growing up as a thinker is noticing which of your own mental factories produce mostly truths and which ones produce junk. That’s just as true on the soccer field as it is in a classroom argument. The debate started in 1979 isn’t settled, and it pops up every time you ask: “How do I know I’m not just making this up?”
Think about it
- If you had a perfectly accurate gut feeling that always gave you the right answer on tests, but you had no idea why it worked, would you be justified trusting it? Why or why not?
- Imagine you’re in a super-realistic virtual world and everything you see is computer-generated. Are your beliefs about that world justified? Does it matter if you can never detect the simulation?
- Think of a time when “common sense” led you wrong. How could you test whether a mental shortcut you use every day is actually reliable?
