What does “existence” mean?

During a recent online discussion I discovered, somewhat to my surprise, that there is no general agreement on what the word “exist” means. Everyone has an intuitive understanding of it but when it comes to an explicit definition of the word there is no consensus, and indeed philosophers have written a vast literature on the topic of ontology, or what exists.

Dictionaries don’t really help; for example Oxford Dictionaries gives a nicely circular set of definitions:

Exist: 1. have objective reality or being
Reality: 1. the state of things as they actually exist
Being: 1. existence.

Of course physicists have a perfectly good operational definition: something exists if it is capable of making a detector go ping. Try arguing that, however, and you’re immediately accused of materialism, physicalism, scientism, being blind to possibilities beyond a very narrow world-view, and a host of similar sins (I plead guilty to at least the first three).

Many want to believe in the existence of things that are non-physical and do not make physicists’ detectors go ping. Such people avoid any explicit definition of what “exists”, preferring to rely on human intuition. I’m often puzzled by the weight given to intuition in philosophy. Yes, it is a guide, but we know that human intuition is horribly suspect and fallible, and unreliable unless corroborated by evidence. As H. Allen Orr says: “a scientific education is, to a considerable extent, an exercise in taming the authority of one’s intuition”.

I thus thought it worthwhile to take the physicists’ “ping” definition and see how it compares with philosophers’ ideas about ontology. Refining the definition a little, I arrived at:

Something “exists” if there is a potential chain of causal links between it and our sense data.

This is an empiricist’s stance, placing our own sense data at the root of our knowledge of the world. Even a pinging detector is useless unless we get to know about it. To adapt Descartes: “I feel therefore I am, and things that cause me to feel are”.

Of course we hardly ever experience anything directly, since even when looking directly at something we are experiencing the photons bouncing off it, not the thing itself. Hence we know about something only because it has affected a thing which affected another thing which affected something else … and ended up affecting sense data. Hence the “chain of causal links” in my definition.

The causal connections need only be between adjacent links in the chain. There might not be a causal connection between the ends of the chain (between the thing itself and our sense data) since, owing to the finite speed of sending a signal along the chain, the signal might not be able to travel that far.

For example, our universe has an “observable horizon” beyond which we can not know about, since even light-speed signals will not have had time to reach us given the finite age of the universe. Presumably, though, stuff still “exists” out there, even if we can’t see it (horrible consequences follow if that isn’t the case, including a violation of the Cosmological Principle, and the fact that material might go out of existence or come into existence as it crossed our observable horizon, as if we mattered).

The word “potential” is included in the definition since many possible causal effects will not, in practice, be realised. Lastly, I should probably remove the word “is” from the definition of “exists” and make the definition iterative: Start with the sense data; Thing 1 potentially affecting it then “exists”; Thing 2 potentially affecting Thing 1 then exists; and so on along the chain. Such a chain is, of course, our mechanism for discovering the world around us.

The above is a definition of whether something “exists”, not of whether we know that it exists. Obviously we can’t know about anything existing beyond the observable horizon, and we can only know about what has produced actual causal effects, not what just has the potential to do so.

The philosophical literature on existent and non-existent entities is extensive, but let’s simply apply the above definition and see what happens.

Do composite objects, such as crystals or fruits or stars “exist”? Yes, these exist, since they are patterns of material, and detectors can be designed to go ping about particular patterns of material. Indeed, this is always the case, since nearly everything is a pattern of lower-level stuff (molecules being patterns of atoms, which are patterns of nuclei and electrons, and the nuclei are patterns of nucleons, which are patterns of quarks and gluons, which … well we’re getting beyond established physics to go further).

What about ideas and thoughts and emotions, do they “exist”? Does pain exist? Yes, since these are manifest as patterns of matter (patterns of electrical and chemical impulses in our brains) and, as above, patterns of matter can quite readily make detectors go ping (an fMRI scanner can read thoughts, though only very crudely as yet).

What about mathematical “objects”, such as an idealised perfect circle, or the number 7, do they exist? Not in their own right, but conceptions of these do exist, as ideas in our brains.

What about properties or attributes, such as the colour red? Does the colour red “exist”? (This is the philosophical Problem of Universals.) Things coloured red certainly do, and the conception of “red” also does in our brains. But “red” doesn’t exist in its own right. This is the philosophical stance of conceptualism, with a long history back to at least William of Ockham.

What about classes of objects, such as the collection of all members of a species, does the class, the species, exist in its own right? I’d say, no, though the concepts certain do, again as patterns in our mind.


Now, suppose one proposed a new type of non-interacting physical particle which interacts with other such particles but has no interaction at all with the known things in the universe. Could that particle be said to “exist”? A similar postulate is that there are faeries which can never be seen or heard or interacted with at all.

One response is to shrug and declare the question uninteresting as unfalsifiable and literally of no consequences. Under the above definition, though, they clearly (ex hypothesi) don’t “exist”.

How about causally disconnected parallel universes in a proposed multiverse? Again, ex hypothesi, causally disconnected parallel universes would not “exist” (though one could invent the concept that they might “para-exist”, along with the unseen faeries and the non-interacting particles). Note, by the way, that some multiverse models propose multiple connected universes, and these universes would exist in the same way that matter beyond the cosmological horizon does.

What about the multiple worlds in Everett’s interpretation of quantum mechanics? Since these go causally disconnected immediately on splitting they would not “exist”.

So that is how a philosophically naive physicist might see “existence”. So far I’m not aware of significant flaws in this way of defining “existence”, nor of any better general definition of the word — but if there are I’d be interested to know about it. Of course those not into scientism would have a fit of the vapours over a definition that is close to: “If we can’t see it then it doesn’t exist”.


8 thoughts on “What does “existence” mean?

  1. Pingback: What does “existence” mean? | As Ric3Hard

  2. fojap

    Reblogged this on fojap and commented:
    I rarely reblog posts, but since I just wrote something in which I declared myself to be a “materialist” and found myself hoping some naive person doesn’t come by and “challenge” me with a silly question like “do thoughts exist”, I have decided to preemptively counter that possibility by reblogging this post.

  3. David Evans

    Does this view imply that Everett’s interpretation cannot be true, or even that it is logically incoherent? By your account, his other universes would not exist even if they did exist.

  4. Pingback: A scientism defence of Logical Positivism | coelsblog

  5. Richard Wein

    Hi Coels. I just got here (to this old-ish post) via your comment at Scientia Salon.

    I would say that the view you express here is based on a somewhat misguided way of thinking about language. Wittgenstein famously said that philosophy is a battle against the bewitchment of our language by our intellect. Unfortunately, I would say that much philosophy remains pretty damn bewitched.

    You gave the following definition: Something “exists” if there is a potential chain of causal links between it and our sense data.

    First, I would say that this sort of definition does not tell us the meaning (or sense) of the word. It just gives us a necessary and sufficient condition for using the word, which is not quite the same thing. I for one would be wary of even calling it a definition. More importantly, it seems to be circular, since it uses the word “is”, a near-synonym for “exists”. You could equally have said “Something exists if there exists a potential chain…”. To make any sense of this we must assume you are employing two different concepts of existence, in the two places. The second sense must be a broader sense than the first, and you’ve told us nothing about that broader sense.

    Competent speakers understand the word “exists” perfectly well, without any need for a definition, at least when applied to familiar sorts of cases. Problems sometimes arise when philosophers invent weird cases, but in those cases we should question whether the philosophers’ usage is even meaningful.

    Take the case of mathematical concepts, like numbers. Mathematicians use the term “exists” fruitfully. They may say, for example, that there exists an integer between 2 and 4, namely 3. That’s a useful way of speaking, and there’s no reason to tell mathematicians that they’re wrong. There’s no need to try to force mathematical usage–which is talking about pure abstractions–into the same mould as the scientific and everyday usage–which is talking about the real world. We can leave these useful established usages alone. Problems arise when philosophers ask questions like, “Do numbers exist?” In my view this question is meaningless. The mathematical usage makes sense within its normal context, in which we’ve adopted a certain axiomatic system of thought (whether formally or informally). But the philosopher steps outside that system, and tries to ask whether numbers exists in some external, metaphysical sense. In doing so, he deprives the word of any sense, since there is no established metaphysical sense for him to use.

    We should avoid assuming that every question is meaningful and answerable, or that words always have the same meaning. We should ask, “Is this question meaningful in this context?” It’s also useful to ask what the alternatives are, e.g. what difference does it make whether we say numbers exist or don’t exist. Similarly, what is being asked if someone asks whether emotions exist? Surely no one wants to suggest that we never feel any anger, hope, fear, etc. But apart from that absurd possibility I don’t know what is being asked. Part of the problem here, I think, is that we don’t usually use the word “exists” in connection with emotions. We usually talk about “feeling anger” or “being angry”. Introducing the more philosophical-sounding word “exists” may encourage us to think that we have found some meaningful new question to ask: “Yes, you feel angry, but does your anger exist?”.

    Now, suppose one proposed a new type of non-interacting physical particle which interacts with other such particles but has no interaction at all with the known things in the universe. Could that particle be said to “exist”?

    What particle? You seem to be saying, in effect, “If such a particle existed, could it be said to exist?”. I think a more pertinent question would be, “Is there any point in proposing the existence of such a particle?” Perhaps theoretical considerations of fundamental physics might give us a reason for doing so, but I wouldn’t like to speculate.

    1. Coel Post author

      Hi Richard,
      Thanks for your thoughtful comments. Here’s some brief replies: I agree that people have an intuitive understanding of the term “exists” and we could indeed leave it at that without further enquiry, but it seemed to me worthwhile to try for a more rigorous analysis of the concept “exists”.

      I realised the “is” problem when writing the piece, so a few paragraphs on from the main definition I gave a version without using that word. I do agree with much of the rest of what you say. A mathematician saying that the number 3 “exists” is using the word in a different way, and I think most mathematicians would recognise that. On the question of “does anger exist” I’d say yes it does, as a pattern, a particular pattern of firing in the brain, in the same way that a tornado exists as a particular pattern of air.

      Finally, on this point:

      You seem to be saying, in effect, “If such a particle existed, could it be said to exist?”.

      I wouldn’t phrase the question that way, I’d more be asking whether the property of being causally linked to the visible universe is a necessary part of “existence”.

  6. osolev

    I assume that the author of this write-up a male with normal testicles.

    Now, here is the test to come to certainty that he exists, in particular when he has another male with normal testicles.

    First, they each observable to the other squeeze very hard with their hands their each one’s testicles, or use a pair of pliers in each hand to grip hard on the testicles, when they want to arrive at greater certainty of their testicles’ existence.

    Do that until they are already feeling excruciating pain in their testicles.

    That should make each of them certain that their testicles exist.

    Now to make each one sure that the testicles of the other also exist: they now grip hard the testicles of the other, until both are feeling excruciating pain in their testicles caused by the other, on each other.

    Now, that is one test for the certainty of existence, and what is existence, in regard to testicles.

    Now do the same exercise on anything and everything that you doubt to exist, like your nose, which you can even cut a small slit in one of the nostrils until it bleeds.

    Now, with things which are not parts of your body, like the bullet in a gun, shoot with the loaded gun’s barrel pointed at and even in contact with your laptop and fire.

    There, that proves to you the existence of your erstwhile good laptop.

    I am sure you now know what is existence, and that you exist and things exist even when you are not around.

    I like you to think on this sentence from me:

    “The default status of things in the totality of reality or being is existence.”

    Go to: http://forumserver.twoplustwo.com/137/religion-god-theology/how-come-god-existing-thinking-truths-facts-logic-1623068/


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