I’m trying to explain to my friends about things existing. I gave them this question: if you place a pencil in an opaque box and close the box, does the pencil exist? They say yes and I ask how do they know and why. All they come up with is “because I put the pencil in there”. I’m having a tough time explaining why the pencil ceases to exist once you close the box.

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    Can you explain what led you to believe the pencil ceases to exist in the first place? Perhaps a misunderstanding of Schrödinger's cat? – reirab Feb 13 at 17:39
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    I am having difficulty understanding the question. Suppose instead I said "I am trying to explain to my friends about sisters. I ask them, do you have a sister, and if they say yes, I ask them if she is female, and they say yes. I ask them how they know. Now I am having a tough time explaining to them why their sister is not female." My scenario appears to me to be the same as your scenario. Can you explain your question to show how your scenario and my scenario are not the same? Or, if they are the same, can you explain why you find it odd that explaining counterfactuals is hard? – Eric Lippert Feb 13 at 18:21
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    Maybe that's because the pencil doesn't cease to exist? This is hardly philosophy. – Carl Witthoft Feb 13 at 19:42
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    When you get frustrated with your friends and take the box home, do your friends also cease to exist? – DarthFennec Feb 14 at 0:04
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    Have you considered asking friends who have not yet developed object permanence? – Ray Feb 14 at 0:06

17 Answers 17


If you shake the box, it rattles. If you measure its weight before you put in the pencil and after, it will have increased by exactly the weight of the pencil. That's how you know the pencil still exists in there.

And if you really want to explore the basic meaning of "existence": how and why do you know the pencil exists before you put it into the box? How and why is this different from the rattling and weight increase?

  • Comments are not for extended discussion; this conversation has been moved to chat. Comments should only be used to suggest improvements of the post. – Philip Klöcking Feb 15 at 23:18
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    Even if you don't measure the box at all - something does exist in the box, which will cause you to see the pencil, when you open the box. So there is something in the box, which is different from an empty box - and we simply call this "being there when I look" = "existing", without any need to define the exact state in which the pen exists if I don't look – Falco Feb 18 at 10:34

I’m having a tough time explaining why the pencil ceases to exist once you close the box.

Because you're trying to explain something which is wrong physically and wrong philosophically. Your friends are correct.

The issue is that you have no proof of its presence or absence once you close the box. That does not mean it ceases to exist. It just means that you cannot prove whether it still exists, or whether it ceases to exist at some point whilst the box is closed, or even whether it ceases to exist at the moment the box is closed and reappears at the moment the box is opened, or flickers in and out of existence, or becomes an alien spaceship when you're not looking.

Absence of evidence does not mean evidence of absence - that's a basic logical fallacy. It simply means we don't know.

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    Also, even "absence of evidence" doesn't really apply to this case. The fact that you put the pencil into the box and haven't opened it to remove it is actually quite strong evidence that the pencil remains in the box and continues to exist. It's not proof, but it's definitely evidence. – reirab Feb 13 at 17:35
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    @reirab Strong evidence isn't conclusive proof though, which I think is where the OP is coming from. Sure, Occam's Razor strongly suggests the pencil is still there. However Teller, of Penn and Teller, has a wonderful "smoking a cigarette" sleight of hand routine involving a pencil, which shows just how wrong Occam can be! I personally think the line of philosophy the OP seems to be falling into is just irrelevant bullshit sophistry, but I'm happy to concede "absence of evidence" for something which is irrelevant bullshit. :) – Graham Feb 13 at 18:19
  • @Graham Occam's razor says that the simplest explanation that fits the facts is the best. If a magician stops in the middle of an act to smoke a cigarette, "they really want a smoke" doesn't fit the facts. – Acccumulation Feb 14 at 22:08
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    @Graham but "just smoking a cigarette" doesn't match the facts that the pencil has vanished (or whatever, not actually seen the trick) so it doesn't satisfy Occam's Razor. – Baldrickk Feb 15 at 12:45
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    @Graham I'm confused on how one can 'violate' Occam's Razor? As far as I know, Occam's Razor is a heuristic used to pick out the best hypothesis in the absence of complete information. Of course it's not going to always result in picking the same hypothesis as the one you'd have picked if you had more information. In the case of being mislead (by a magician, statistics or otherwise), forming a hypothesis based on what you knew at the time and it later being revealed to be 'wrong' in the presence of more information doesn't 'violate' Occam's Razor. – tangrs Feb 17 at 4:04

The assumption that the pencil continues to exist - even when the box is closed - is the most simple hypothesis which explains all relevant observations. E.g., the observation that the pencil exists when opening the box, as @Mauro ALLEGRANZA explains.

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    Most simple hypothesis is usually referred to as Occam's razor – user2813274 Feb 13 at 15:14
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    I think the word intuitive is a better description than simple. I don't see why ceasing to exist must be more complex than continuing to exist. – Cell Feb 13 at 20:36
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    @Cell I mean „simple“ not „intuitive“. Intuition can be a deceptive adviser. The hypothesis of continuous existence is simpler than the opposite hypothesis. Because the opposite hypothesis has to explain how opening and closing the box destroys and recreates the pencil. – Jo Wehler Feb 13 at 21:15
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    @Cell The OP speaks about "explaining why the pencil ceases to exist once you close the box". – Jo Wehler Feb 13 at 22:05
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    @Anush Of course, this belief is simple. But necessary and difficult is the additional explanation how things vanish and reappear; see my previous comment. – Jo Wehler Feb 14 at 17:22

You are assuming that existence is a phenomenon that can undergo sudden state changes. Or in simpler words: That things can cease to exist and came (back) into existence instantly and without observable side effects.

As Carl Sagan said: “extraordinary claims require extraordinary evidence”

Your claim has no supporting evidence. No such sudden stage changes have ever been observed or measured, not directly nor indirectly. No other evidence of such stage changes exists, to the best of my knowledge. All our experience, all our physical and other natural laws indicate that objects persist even when not observed.

There is a philosophical argument that Nietzsche made (can't remember which book, sorry) in that an object is defined by its interactions with other objects. If you were to somehow remove all interactions with other objects, the object is indistinguishable from not existing at all.

However, you only remove simple visual observation. There are many, many other interactions, including gravity and electromagnetic forces both with the outside and the box itself. Eliminating all interactions with all other objects is impractical. It also suffers from the sudden state change problem: How are these interactions restored by the act of opening the lid of the box, at which time the pencil will certainly be observed to be in the exact same place again?

Also, if we complete the thought experiment, and even postulate your non-existence theorem, our experience shows that if we resume observation, i.e. open the lid, the pencil will exist again in the same place and position as it was before. Where is the information about its position, rotation, relative movement (or lack thereof), and all other conditions of that object stored? Whatever that storage of information is, is it not indistinguishable from continued existence of the object?

  • I think your Nietzsche book is The Will to Power: "The properties of a thing are effects on other 'things': if one removes other "things,' then a thing has no properties, i.e., there is no thing without other things, i.e., there is no 'thing-in-itself.'" – Lord Farquaad Feb 14 at 22:31

If you place a pencil in an opaque box and close the box, does the pencil exist?

This is a Metaphysical question to which we do not know the correct answer. But here are some philosophical views

Idealism : The pencil does not exist when no one is watching

The mind is what creates matter, if something is not created by any mind (i.e : inside an opaque box), then it does not exist.

But different idealist philosophers have different stories to say, for example : George Berkeley would argue that even if the pencil is an illusion created by our minds, it still exists inside the box because it is always in the Mind of God : When we are not watching, God is watching.


According to Leibniz's Theory of Monads on the other hand, the pencil would vanish from existence and reappear when we bring it back to our consciousness. But Leibniz does not think that the pencil is a mere illusion created by our minds, but rather that real nature of matter (that is : its substance) is mind itself.


Dualism and Materialism : The pencil exists inside the box

Different flavors of dualism hold that both matter and mind do exist separately, While Materialism holds that only matter exists : But according to both Materialistic and Dualistic philosophies : The pencil is in the box.

In my opinion, I would argue that probably (like 99.99%) the pencil is in the opaque box. And here is my argument :

I rely on abduction, Ockham's razor, Uniformitarianism and pragmatism, to come to the conclusion that the pencil probably exists in the box.

Different modes of reasoning make it possible for me to conclude that there is no reason to believe that things disappear, when you think about it :

  • The idea violates Uniformitarianism (that the Universe works the same way even when we were not there to see it)
  • The idea is more complex, since it requires things to disappear and reappear, and your mind has to do all that work. (applying Ockham's Razor and abductive reasoning). https://plato.stanford.edu/entries/simplicity/#Int
  • The idea is meaningless according to pragmatism (only what can be practically applicable is meaningful)

Additionally, if the pencil is just a mind illusion, then what it is that makes it permanent, and therefore sets it apart from all the pencils that I have seen in my dreams, that are not permanent?

I know that pencil I put in the box in my dream is an illusion, which makes me sure that I probably would not find it there while awake or in another dream.

Therefore, the 'real' pencil has to be something more than what we call illusion, an illusion that persists, an illusion that the Universe does not seem to forget about...?

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    it is always in the Mind of God Or from Spinoza's point of view, God is inside the box with the pencil, and inside the pencil itself. – Graham Feb 13 at 16:28
  • "According to Leibniz's Theory of Monads on the other hand, the pencil would vanish from existence and reappear when we bring it back to our consciousness." So then what would be his answer to the question of why we can trip over objects that neither we nor anyone else around us is aware of? – Mason Wheeler Feb 13 at 23:27
  • @MasonWheeler, if you trip over something you cannot see, it is still brought back to your consciousness, but not in a visual form. As for Leibniz I do not know what would be his answer here. – SmootQ Feb 14 at 9:18
  • Yes, but not until after you've already physically made contact with it. – Mason Wheeler Feb 14 at 11:57
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    You probably should add "experience/knowledge" to your set of reasoning modes. If it was not a pen but an ice cube, the ice cube will cease to exist at some point, but this is within experience, as opposed to the situation of disappearing pens. (my pens always seem to disappear, but I guess this is another problem) – Stefan Feb 15 at 13:22

Simplicity is a criterion for theory or explanation selection. It can clash with other criteria such as explanatory reach. Also there is no agreement on the nature of simplicity. Intuitively, I suppose, it denotes ontological parsimony or theoretical elegance - notions which themselves stand in need of clarification.

The question asks 'how they know'. There is no necessary connection between simplicity and knowledge. Simplicity is a sound methodological rule - but why ?- but a theory or explanation can be simple but false.

I am inclined to say that we do not know that the pencil exists in the duration. (1) The belief that it does is not immune from error; (2) in the circumstances described we cannot confirm or verify the pencil's existence; (3) there is no causal connection between the pencil and our mental state of believing in its existence (invoking a causal theory of knowledge here); and (4) no epistemological intuition of continued existence is available and reliable.

At best, that the pencil exists merely fits - is most consistent with - our 'web of belief' (Quine). Given our overall view of the world, in general the continued existence of unobserved objects best fits our theoretical and explanatory assumptions. I don't deny this but I also don't see how, granting it, we know that the pencil exists in the situation described.

The crucial point is, however, that these sceptical considerations against the assumption of the pencil's existence equally apply to your own assumption of its non-existence.

  • @TG2. Fine, thanks, I appreciate the clarification. As a Moderator I have to keep an eye on language that might cause offence - not to me, I don't mind but there are community rules. Anyhow, it's behind us now and I'll look forward to your further contributions. Best - Geoffrey – Geoffrey Thomas Feb 13 at 15:23

I’m having a tough time explaining why the pencil ceases to exist once you close the box.

You're having trouble because your claim that the pencil ceases to exist relies directly on a philosophical proposition that your friend does not accept. That would be something along the lines of "only those things that I directly detect with my senses exist." If you accept that as true then you're taking it, or something substantially equivalent, as an axiom.

Your friend takes a different view. He claims that "because [he] put the pencil in there," it still exists. That seems to belie a philosophical position directly in opposition to yours: that objects' existence is independent of whether anyone observes them. A number of additional assumptions presumably accompany that, such as that it requires the operation of some force or agent to cause an existing object to cease to exist, and your friend is probably interpreting your claim to include that no additional action or forces in play. By that reasoning, his rejection of your proposition is entirely logical.

Overall, when you say

I’m trying to explain to my friends about things existing.

, I get the impression that you think you're trying to convey facts. You are not. Rather, you are advancing philosophical position that is neither provable nor disprovable -- in effect, a definition for what it means to "exist". However, inasmuch as that definition is inconsistent, in my experience, with common usage of the term, it should not be a surprise that your friend resists the idea.

  • +1 for addressing the difference in viewpoint and not just trying to prove the OP wrong. – Cell Feb 16 at 3:07

There are two hypothesis, assuming there is no gimmick in the box (i.e. a magician's box with a false bottom):

  1. The pencil ceases to exist while the box is closed, but returns to existence when it is opened.

  2. The pencil remains in existence while inside the box.

If you measure the weight of the box before and after you put the pencil inside, the weight is different, and that difference is equal to the pencil's own weight. As someone else mentioned, the box may rattle if you shake it inside, and its center of mass will shift when tilted.

With hypothesis one you need to explain why the phenomena of the previous paragraph happen if the pencil does not exist while the box is closed. Hypothesis two renders those observations' explanation moot (it happens because there is an unseen pencil inside the box).

Applying Occam's razor, we can discard #1. Therefore the pencil does not cease to exist once the opaque box is closed.


Existence of something like the topic's pencil is unrelated to you observing it or not. Assuming we don't take into account hundreds of years intervals (one way for the pencil to disintegrate due to the passage of time) in the case the box is not perfectly sealed from the external environment (or any other such variables) and assuming nothing else is inside that may affect it, the pencil does exist.

This is related to matter and energy conversion. If the pencil wouldn't be there, it would mean it was converted to something else (due to variables like above).

  • But in the same sense, your lifetime experience with natural phenomena is based on observation. Obviously we don't see things disappearing in front of our eyes for no apparant reason thus you know the pencil is still there. But why should we trust your past observations instead of the present one? – Cell Feb 13 at 20:40
  • Because in the instance we talk about you actually cannot do the observation. Therefore you cannot make a determination of something's state. – Overmind Feb 14 at 6:16

Since you and your friends are doubting about existence, I'll tell you this: It depends on the box...

There are a lot of magicians that would love to contradict you by bringing their own box. They will let you put a pencil inside, say abracadabra and open the box again. For your surprise and your friends', the pencil will be gone. Vanished out of existence. Don't panic, after another magic conjure it will probably reappear!


First of all, you need to understand that exist means to be present. If you are asking whether the pencil object ceases to exist when in the box, definitely it is existing although you are not able to see it with your unaided eyes because it is in the opaque box. If you used a scanner then it could be seen.

In other words, you are asking if somebody covers my eyes with a piece of cloth, does the entire world cease to exist? Definitely it is still present.


What you call a "pencil" - a pattern in the way certain subatomic particles are arranged, exhibiting certain properties in interactions with other things - continues to exist even inside the box. The conditions for observing some of those interactions continues to exist (e.g. you can measure mass, mass distribution, changes in mass distribution following certain changes in orientation with respect to a gravitational field, production of certain sounds given certain applied forces, and interaction with other electromagnetic frequencies to which the box is not as opaque) even if you have temporarily removed your capability for observing other of those interactions. At any time, whether in the box or not, you can only observe some of the interactions associated with the pattern-label "pencil," due to our limitations as observers. By putting the pencil in the box, you are slightly modifying the set of interactions you can easily observe.

Also keep in mind that interactions with visual wavelengths are not the only interactions we use to define "pencil;" for example there are some objects which look and/or feel like pencils but don't write like pencils (e.g. they might write like pens or not write), which many ontologists would likely say is a defining characteristic, though it depends on the purpose for which the label is being applied. You're probably not easily able to observe those properties at all times even when the pencil is not in the box.

By contrast, let us consider what happens when I put a small piece of dry ice in the same box, and let that box sit for some time at "normal" room temperature and pressure. In that case, the dry ice does actually cease to exist. This is because what we call "dry ice" definitionally refers to the solid form of carbon dioxide, an arrangement of particles that has certain properties in interactions with other things. When the carbon dioxide has all sublimated to the gaseous form, it no longer exhibits those properties.

If the dry ice box were airtight, one could still observe (with a very sensitive scale) that the mass of the box + dry ice was equal to the mass of the "empty" box plus the mass of the dry ice, and if the right equipment were available one could theoretically recapture all the carbon dioxide, and re-form the dry ice. If the box were not airtight and left alone long enough, even the mass difference would no longer be observed because the extra carbon dioxide would escape, and relative fractions of different gases would equalize with the surrounding atmosphere.

However, if the dry ice box (airtight or not) also contained a plant, even [at least some of] the carbon dioxide molecules would no longer "exist" but would have been disassembled and reassembled into patterns that we might call "gaseous oxygen" and "cell wall" based on their properties in interactions with other things.


I'm not smart in this field and almost no other topic, so first I want to try and understand why we need this constant to be an opaque box. Is it because we can't allow light through to possibly consider it not existing? For example, say I put my left over pizza in my fridge to prevent it from spoiling. I can't ask that my pizza may or may not exist because I can't see it, unless I open the fridge again for the reason I stated before? How about if you paint over an item with Vantablack? One last thing I want to add, can we just use common sense like his friends are and say for example, "It still exists because no item as common as a pencil can just disappear in thin air?"

  • Welcome to PSE. I didn't downvote, someone else did. They did so because your answer needs refinement to count as philosophical. I suggest you read the other answers to get a clearer idea of how philosophical answers go. Everything comes with practice. It might be a good idea, just for a while, to offer comments rather than answers - just until you get the swing of things. Only a suggestion. I look forward to your future contributions. Best - GLT. – Geoffrey Thomas Feb 13 at 21:21
  • I agree. Pencils can't just sprout wings and fly away :D – Bread Feb 13 at 23:42
  • The word opaque was used to imply that it cannot be perceived i.e "does something exist if it is not perceived" Of course most answers are taking the question too literally and writing about weighing the box and how physics works. Pretty unexpected for philosophy stackexchange. – Cell Feb 14 at 18:53

This is at the root of a key confusion people often have between the endurable model of the world and the perdurable.

In an endurable model of the world, the world is viewed as snapshots, thin slices of time. While the pencil is in your hand, it's easy to point and say "in this time slice, there is a pencil right here." Once you put it in the box, it's harder to do this. Unless you have X-ray vision that permits you to directly observe the pencil, it's hard to say "in this time slice, it's right here." We have to fall back on the less strong "we don't know." Note that this is less strong than saying "there is no pencil in this time slice."

In a perdurable way of thinking, we connect the existence of this object through time. In most cases, this is obvious. If we are holding onto the pencil, it's typically easy to argue that the pencil continues to exist in my hand. Once it is put in the box and the lid is closed, most people find it reasonable to assume that the pencil continues to exist inside the box. They find it reasonable because they have done this countless times in their life and every time they've found the pencil is there when they open the box (or it's a magic trick). However, a 1 year old does not demonstrate this way of thinking. For them, put an object in a box and it ceases to exist until you open it again!

Why these disagreements? Well perdurable models are tricky. The most famous issue of this kind is the Ship of Theseus, which is similar to your box but doesn't have an "unknown" element because you can "watch" the ship through the entire process.

From there, one can dive into the question of whether the pencil exists in an ontological sense, or if all you can state is whether an image of it exists in your mind. That's a fun rabbit hole to explore.

But in the end, the purpose of the whole exercise is not to demonstrate that the pencil does not exist while it is in the box. It's to demonstrate something else, something that only makes sense if you draw the conclusion that the pencil did not exist while it is in the box. For example, one line of reasoning that can be drawn from The Ship Of Theseus is that the ship is actually only a concept that exists in your mind. Some thing does exist as part of reality, but it is only a "ship" as part of your mental image of what this thing is and does. This line of reasoning is consistent, though typically unpopular.

You might also make a statement about our ability to know things about reality. If you bet your life that the pencil exists while the box is closed, you might be in trouble when you failed to observe my assistant opening a false bottom in the box, taking the pencil, and throwing it in a woodchipper, ending its pencil-ness. A worldview which encourages one not to take such a bet might explore the question of whether the pencil existed at all.


You haven't given specific objections they had, but I think there's two points that would be helpful to make.

  • As others users commented, the pen's existence can be verified by shaking the box. By "opaque" you probably meant opaque to all senses, not just vision - ie. the question is not a puzzle. You can enforce this by slightly modifying the question: You watch a man on live video put the pen in the box. The feed is one way.
  • One common method of proof is counterexample.
    • What if the pen teleported away?
    • What if the box has a hidden grinder?
    • What if the man used sleight of hand to whisk the pencil away?

These do also run into the issue of using an unconventional meaning of "exists" - specifically, we mean "exists inside the box", not anywhere. The hidden grinder is an exception, and should give you an idea of how to modify further if this semantic hurdle is a problem.

  • I am somewhat confused with what you are trying to say. If you have a reference this may help make your answer clearer and give the reader a place to go for more information. – Frank Hubeny Feb 14 at 8:48

If you are placed in an opaque box, and the box is closed, do you cease to exist?

  1. Let's suppose that you and a friend are in a closed suite, with no windows. The suite contains two rooms, with a door between them. There are no windows in either the divider wall or the door. The door is open. May I assume that both you and your friend exist?

  2. Suppose you are both in the same room, and you close the door. May I assume that both you and your friend still exist, since you can both verify each other's presence in the room?

  3. Suppose your friend opens the door, and goes into the other room. May I assume that both you and your friend still exist?

  4. Now your friend closes the door, so that you and your friend are now in separate rooms. In other words, your friend has placed you in an opaque box, and closed the lid. Do you still exist?

Note that it can equally well be said that you have placed your friend in an opaque box, and closed the lid. If you still exist, then it can equally well be said that your friend still exists.

Suppose your friend is dressed up like a pencil, complete with an eraser and a writing tip. You have placed a pencil in an opaque box, and closed the lid. If you still exist, then so does the pencil.


Well, as always, when judging the plausibility of an idea, we must bring to bear all relevant prior information that we have.

So, when I see someone place a pencil in a box, and I ask myself, 'does the pencil still exist now that it's been placed in a box?' I must consider what I know about that person, the pencil and the box.

If I know that the box or pencil are somehow special, e.g., special 'trick' ones with elaborate mechanisms for making something disappear, I might guess that the pencil no longer exists inside the box. If I know the person is a magician, I might again think they are up to something and that the pencil may have disappeared from the box. If the person approached me unprompted in this scenario, I might assume they are playing a trick on me, and that it would disappear. And so on and so forth.

But generally, based on my prior experience with putting things in boxes, they tend to still be there when I open it the next time. So I would probably consider that to be the overwhelmingly most likely outcome. This is not, however, a deductive proof that the pencil continues to exist.

In summary, I think the closest correst statement to the one you are making to your friends is, 'our uncertainty about the existence of the pencil should increase once it is placed inside the opaque box'.

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