What is the fundamental nature/ontology of knowledge? Is knowledge a physical state? Is knowledge a specific arrangement of physical particles in a brain, a book, a solid-state drive, a GPU, etc.? Or is knowledge fundamentally non-physical, existing in some non-material (idealist? spiritual?) realm/domain/dimension of reality, akin to how mathematical platonists would claim that mathematical abstractions objectively exist outside of space and time?

For broader context, see the related questions:

Is non-physicalism reasonable?

How can something non-physical exist?

What are examples of non-physicalist approaches to acquiring knowledge?

Is the fundamental nature of knowledge intimately linked to the fundamental nature of minds (consciousness)?

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    I think the real question is why would one entertain the possibility of knowledge being non-physical? What would be the purpose of this exercise? Commented Mar 6 at 19:12
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    This is like asking if joy is non-physical. Electromagnetic elements are physical, our interpretation of them is metaphysical.
    – RodolfoAP
    Commented Mar 6 at 20:00
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    It depends on one's metaphysics of abstract objects. To some (realists) they are non-physical ideal entities, to others (nominalists) they are shared linguistic entities, so not quite arrangements of physical particles but rather labeled sets/classes/types of such arrangements with labels linked to the arrangements themselves by physical recognition procedures.
    – Conifold
    Commented Mar 6 at 21:02
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    @YuriZavorotny, because such questions are important to a right understanding of reality. See for example philosophy.stackexchange.com/questions/110012 on why such assumptions may be harmful to the search for truth. For a good example, consider 'i' (a.k.a. √-1). By its nature, you can't measure 'i'; it is immaterial. And yet it is incredibly useful. If 'i' can exist as an immaterial construct, how do you turn around and argue that ideas (and knowledge) cannot? How do you measure logic and reason? Can information exist outside of its physical manifestation? These questions matter.
    – Matthew
    Commented Mar 6 at 21:43
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    It may just be semantics but there is a difference between knowledge and understanding. Understanding is an abstract concept and difficult to describe. Knowledge can be physical (written in a book) but understanding the knowledge contained within a book is an abstract process. Commented Mar 6 at 23:57

16 Answers 16


I think this is unfortunately one of those questions where there's no canonical answer, and so the answer you get from each person really only tells you about their beliefs and not much more.

The majority of professional philosophers are physicalist, but it's only JUST a majority, as small of a majority as you could get. https://survey2020.philpeople.org/survey/results/4874

Thus, if you cared what the bulk of professionals in philosophy think, they think knowledge is encoded in physical brains, but only 52% believe that, and they obviously may be wrong.

There's still a lot of work to be done in understanding cognition and consciousness and how our minds work. It's not called "the hard problem" for nothing - it's really really hard!

  • And then at least some of the physicalists are instrumentalists, who think even if you ever measured a bit of knowledge physically that would only be a measurement and say nothing fundamental or true about the world per se...
    – Stian
    Commented Mar 7 at 20:08
  • Hi TKol in the distinction between "physicalism and non-physicalism" do they count things like e/m waves, electrical energy, quantum fluctuations, dead cats, and what not... the fermions, bosons, etc... all as being "physical"... and leaving as "non-physicalism" strictly "other-stuff-types, or like soulds or ideas or locations or entities or dimensions or what??". If you know. Is there a firm line, or do people self-identify? Or a list of what stuff belongs on which side? Commented Mar 9 at 5:39
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    @AlistairRiddoch yes, physicalism includes anything that physicists study. The common word used to be 'materialism', and I'm not entirely sure why that went out of fashion, but one of the reasons may be that it created confusion. People would (and still do, sometimes) think "well if you think only the material exists, then you must not believe in energy, because energy isn't matter", but... clearly, no, any materialist / physicalist believes in energy, because energy is the concept we use to describe how material changes and moves, and clearly materialists believe material changes and moves.
    – TKoL
    Commented Mar 9 at 7:53
  • Great info and helped me along a little in my quest to understand "what I am"... in philosophical terms, if self-identifying to others in a community of philosophers. My education in philosophy in uni, got cut short by the arrival of a bunch of kids... so I am close to uneducated in the technical terminology of the field. I think I need a new calssification to describe myself. I am unique as far as I know. I think a "puritanical fundamental physicalist". Not quite the same as an average, run-of-the-mill, everyday physicalist. Commented Mar 9 at 8:02
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    @TKoL Another reason the term got replaced is probably because materialism is used to denote a system of values focused only on the material goods (opposed to honor, legacy, etc).
    – rus9384
    Commented Mar 9 at 9:05

"Knowledge" is an abstract concept. It is a convenient label, generally considered to apply to true beliefs (with considerable wiggle around what exactly that means, and how one might know about knowledge).

A specific arrangement of particles in a brain may correspond to knowledge but is not knowledge itself. There could be some super-natural dimension, as you suggest, but that really comes down to the same thing: whatever the "storage" is... again, it isn't knowledge.

There are two pencils on the desk in front of me, but that isn't the number two, and never will be.

You could argue that, as an abstract concept, knowledge doesn't actually exist. Or that the abstractions of math don't either. If you like. That seems less convenient, but if it's important to how you want to structure things, can be a reasonably self-consistent approach.

  • Or that the abstractions of math don't either - mathematical platonists would beg to differ.
    – Mark
    Commented Mar 6 at 19:22
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    @Mark Sure. As I said, one could argue that (and people have) — but it's not like there's a settled answer.
    – mattdm
    Commented Mar 6 at 19:24
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    An arrangement of particles in a brain, or pencils on a desk, is an abstract concept, too. Consider the arch. An arch is an arrangement of bricks (or stones, concrete, etc), and it is also an abstract concept. Arrangements are abstract. Specifically we could identify an arrangement with the set of its possible instances. And so it is conceivable that knowledge, being also abstract, could be an arrangement of objects; a set of possible instances that constitute knowledge.
    – causative
    Commented Mar 7 at 2:50
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    I think there's confusion in OP's question about the concept of "knowledge" (which is a label as you say, non physical) and where/what all instances of knowledge are. And then you could ask or argue, "is there a type of knowledge that is non physical/stored on non-physical entities".
    – Jemox
    Commented Mar 7 at 11:02
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    @causative I suppose I can accept that interpretation: that the representation of something can repeatedly become or cease to become knowledge. Sort of like the state of something being a poison. I don't think many people would deny that if the biochemistry the poison acts on no longer exists that the poison no longer exists in that it is no longer a poison, even though the material itself continues to. And if the biochemistry begins existing again it becomes a poison again.
    – DKNguyen
    Commented Mar 8 at 20:25

Knowledge is typically taken to be non-physical. For instance, to ride a bicycle, you use what epistemologists might call knowledge-how (SEP). If you tie your shoes, for instance, you can't go to the store and buy a pound of shoe tying in the same way you might for okra. However, that comes from the caveat that according to a typical physicalist set of presumptions, that knowledge is somehow encoded by physical things like neurons.

There is typically a duality when dealing with information and knowledge and mental states that reflects the traditional division of mind-body duality. Consider that software and hardware are such a dualism. In communication theory, one talks about the medium and the message. And of course, the classic discussion is about mind and body. So, when most people refer to knowledge, they are talking about something that is not concrete, but abstract. In the same way a painting is more than paints, knowledge is more than connected neurons, or semantics is more than syntax.

In typical usage, therefore, what a person knows dies with them, unless it is written down and read by someone else. Books are seldom described as knowing things, but rather are treated conceptually as containers for knowledge. On the classical view of knowledge, it must be at least justified, true belief, and belief is a state that is rather peculiar to philosophical agents.

  • Knowledge is typically taken to be non-physical - What would be an example of an exception? Eliminative materialism? Reductive materialism?
    – Mark
    Commented Mar 6 at 22:50
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    @JD -- and that I think is the question here: is the "physicalist" model adequate? And if not -- why not? And if it is, then why we keep entertaining "idealist" models? After all, we know for a fact that any kind of knowledge can be recorded on a physical media (and, therefore, exist as such). Why, then, would one propose that this model is not adequate enough and that knowledge must also exist in some non-material form? Commented Mar 7 at 0:18
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    "Consider that software and hardware are such a dualism" - I would actually say that's a perfect example of monism. Hardware and software are both encoded in physical forms, and software is implemented through physical mechanisms (logic gates).
    – TKoL
    Commented Mar 7 at 8:12
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    @TKoL Software is an abstraction. Ot is no more physical than mathematical pairs of functions defining circles or the truth-aptness of propositions. 1s and 0s are abstract objects, not physical ones.
    – J D
    Commented Mar 7 at 13:23
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    @TKoL That's because you are confused. I never said anything remotely resembling what you claim I said.
    – J D
    Commented Mar 7 at 16:40

Knowledge is information about facts. It is stored in the memory of our brain and can be retrieved by suitable mental processes.

Apparently, information is non-physical.

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    "Apparently, information is non-physical" -- what about information processed by computers, or information stored in a hard-drive, or the information on a vinyl record. Would you describe such information as non-physical too? In what sense a vinyl record is non-physical? Commented Mar 6 at 23:46
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    @YuriZavorotny I distinguish between information and the carrier of the information. You name different carrier of information, while my point is the information. It is independent from the carrier. Analogy: A printed book has pages. The pages are not the information but the carrier of the information.
    – Jo Wehler
    Commented Mar 7 at 5:19
  • I understand that we can make that distinction because information is independent of any particular media. Any physical carrier can be destroyed -- but all information that was recorded on it gets transferred on some other media (smoke, heat radiation, etc). Therefore, any information survives only because it is (re-)recorded someplace on some physical media. And, therefore, the information is inseparable from the media it is currently recorded on. Commented Mar 7 at 7:23
  • This apparent paradox -- that information is both independent and inseparable from its physical carrier -- is, I think, the reason for all this confusion. Still, I think that the fact that no information can exist outside of its carrier(s) should be enough to describe it as physical. Commented Mar 7 at 7:26
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    @YuriZavorotny You have an interesting perspective. Why don't you just go ahead and post an answer of your own?
    – Mark
    Commented Mar 7 at 11:57

Knowledge is information that is analyzed, interpreted, understood, assigned meanings and linked with other pieces of knowledge within the mind.

Knowledge can exist only within the mind. If you write down what you know, it becomes information again. Whoever reads it must analyze, interpret and understand it in order to turn it into knowledge.

Knowledge is immaterial just like all information is. Knowledge has no measurable physical properties at all. There are no laws of physics governing knowledge, no equations for calculating knowledge, no parameters to put in such non-existing equations.

  • Since you are linking the nature of knowledge to the nature of the mind, can you please clarify what your stance in philosophy of mind is? There are different proposed solutions to the mind-body problem, such as different versions of dualism (interactionism, psycho-physical parallelism, occasionalism, epiphenomenalism, property dualism) and different versions of physicalism (behaviorism, identity theory, functionalism, nonreductive physicalism, eliminative materialism).
    – Mark
    Commented Mar 7 at 12:29
  • To me the mind is just the brain's capacity to process information. The mind decides what the body does. I don't see any problem with that and I don't care which philosophical stance it represents. Commented Mar 7 at 14:22
  • Re "Knowledge is immaterial just like all information is": That's quite obviously wrong. Information is "Imprinted", sometimes quite literally, on some "physical" medium, even if that medium is bare spacetime and the information is its vibration in the form of gravitational waves. While the specific medium is mostly irrelevant, some medium is indispensable. I'd admit that the issue is less clear with "qualified" or "understood" information, a.k.a. "knowledge". But in the end, there is no reason to believe that this addition is more than just just additional (meta) information. Commented Mar 9 at 18:30
  • There is an entire field of mathematics concerned with information content, transfer and storage, founded by Claude Shannon. Commented Mar 9 at 21:24
  • @Peter-ReinstateMonica The fact that information is always "imprinted" on some physical medium does not mean that information itself is material stuff. Information is a description of the physical object it is encoded in. The shape of a radio wave, the configurations of ink on paper, ones and zeroes in a computer. Commented Mar 10 at 4:58

What is knowledge is subjective on the entity that is able to know it. Potentially, everything is knowledge for something.

Knowledge doesn't exist in itself; it's an emergent concept, a shortcut of language and thought, like "temperature", "solid object" or "light".

Given a choosing entity (good luck defining what that is) they will make choices that depend partly on what they "know". What that means in practice is that there are certain arrangements of physical entities, be it ink molecules, light, biological neuron connections, weights in an artificial neural network or whatever, that this entity uses to make choices on what to do (which includes determining what to register as new knowledge to be used for later choices). The criteria on what arrangements count as knowledge is totally dependent on what this entity is.

Note that this definition is necessarily broad. A blank piece of paper might be said to contain no knowledge but it can be used to make decisions or learn facts about what paper is like. Same for a mountain slope that will hold information about itself which can be considered valuable in certain circumstances, such as the objective of a space probe on Mars, which goes there specifically to acquire this knowledge.

If you want to narrow it down you'll have to speak about important or useful knowledge, both concepts that deepen the dependence on evaluations made by the entity that possesses it (or could).

I guess you could define "knowledge" as anything that some entity in some situation would consider as such, but I'm afraid that you'd find that this would encompass the whole Universe and all its component parts.


By definition, knowledge cannot be "physical". Go through a simple logic exercise. One could, in principle, learn something that supports the truth of physicalism. In this case, knowledge COULD be physical. However, one could also learn something that definitively showed that physicalism is untrue of anything in our universe (decisive evidence for idealism, say). In the second case, the knowledge could NOT POSSIBLY be physical. Yet the two postulated bits of knowledge, as a general category, are not fundamentally any different. They should be of the came ontology. So -- knowledge as a category, cannot be physical.

The most useful ontologic framework I have found, is Popper's 3 worlds. See https://tannerlectures.utah.edu/_resources/documents/a-to-z/p/popper80.pdf Popper articulated three types of things in this world, those things with time and location properties, those with just time properties, and those with neither. Matter is in world 1, experiences in world 2, and ideas/abstractions in world 3. Knowledge is in the third world, it has no time nor location intrinsic to it.

  • I would rather suggest that knowledge exists only in World 2, i.e. the human mind. Knowledge is interpreted and understood information with a meaning. Interpretation, understanding and meaning are purely psychological things existing only within a conscious mind. World 3 is the accumulated history of human civilisation, all the actions by all people, all man-made changes to World 1. Commented Mar 7 at 7:43
  • Through our senses we input information from and about World 1. In World 2 we process that information, interpret, analyze, understand, assign meanings, turn it into knowledge. Through our muscles we output information to Worlds 3 and 1, Commented Mar 7 at 7:49
  • @PerttiRuismäki -- I think that in some cases, we see leakage between Popper's three worlds, and more interaction and "fusion" elements than his thinking suggests we should see. I use his model as a "useful framework" for understanding the world but far from a rigid constraint. Relative to we humans, I agree the primary mode of knowledge is as you describe. BUT - our unconscious System 1 also has knowledge. And unconscious AI gather knowledge, and can act upon it. Generalizing universals from the role of consciousness in our own higher level processing is overgeneralizing.
    – Dcleve
    Commented Mar 7 at 14:38
  • I currently have a chat running with Ludwig V and Marco Ocram that has been exploring ontology issues, and has drifted into three worlds and pluralism. There might be a good place to do further discussion: chat.stackexchange.com/rooms/151765/…
    – Dcleve
    Commented Mar 7 at 14:42

Sticking my neck out ...

Before experiments demonstrated quantum entanglement to be real (instantaneous "communication" of entangled states that, sadly, can't be exploited), it was easy to test if knowledge/information (are the 2 interchangeable?) was physical/not? If information can achieve Faster Than Light (FTL) speeds, it "has to be" nonphysical (matter is slower than light and the fastest energy is light). What is it that which is neither energy nor matter?

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    I think this is only one (albeit interesting) way that knowledge could be non-physical.
    – usul
    Commented Mar 8 at 21:00

I believe that knowledge in its absolute sense is not countable. That unique knowledge, then, is nothing but beingness or existence. Again, it is nothing but consciousness. In other words, absolute knowledge is / must be always with consciousness.

One can stick either to these concepts - "no knowledge without consciousness" or "no consciousness without knowledge". Again, from our daily experience, after deep sleep (as if we were dead) we feel like knowledge (even though this is not absolute knowledge) is recollected from somewhere. That is, there must be some connection between knowledge and consciousness. All these show that knowledge and consciousness are synonymous in the absolute sense. So we can say that knowledge transcends physical and non-physical state. A thing that is related to physical as well as non-physical must be something more than these two, isn't it?

If something is non-physical, is it capable to grasp / apprehend / realise something physical? Similarly, if something is physical, is it capable to grasp / apprehend / realise something non-physical? So I am asking -- "Are these two routes possible in the case of knowledge? Or what should it be?"


Yes, it is non-physical. But the question is: are intellectual people non-physical? Of course not!

Why is it important?

Many people are just not interested in knowledge, so those who seek it make it physical because knowledge itself can be non-physical but from where we get it becomes tangible; hence, it is non-physical in physical form.

  • What does mean: knowledge is "non-physical in physical form"?
    – Jo Wehler
    Commented Mar 7 at 6:56
  • Well knowledge itself is not physical but the things (people, books, or other tangible things) from where we get knowledge are physical. Here, another question comes. Is knowledge of the human mind physical which is not obtained by any external sources? No, it is non-physical. At least, that's how I think. You may disagree. Commented Mar 7 at 16:01
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    I agree that knowledge in our mind is non-physical. - If I write down my knowledge on a sheet of paper and then burn the paper, the physical carrier of the knowledge, the knowledge still exists. The physical paper was totally irrelevant for the knowledge, it was only a means to communicate knowledge.
    – Jo Wehler
    Commented Mar 7 at 16:12

"What Is Knowledge" - I have to say, this question gave me a pose. After a while, I realized that I didn't have an answer. From the human point of view, we are missing a lot of answers. What is the matter? What is life? What is knowledge?


Yes. Non-physical. Abstract.

Knowledge is understanding, concepts, skills, experiences.

We can store and transfer knowledge using physical medium to capture the concepts. But the knowledge itself is abstract. Requires a host to exist.

If there were no beings to know things, there would be no "knowledge".

It may be worth noting that knowledge is not exclusively a human phenomenon... many animals collect and store some knowledge too.


The selected answer seems like the best one, to me. I just want to note that there are more options than non-physical vs physical-state-of-the-brain.

In fact, it is completely uncontroversial that there is no physical state of the brain which is sufficient for being knowledge (with the possible exception of some weird examples). The world outside the brain needs to be in a certain state too -- at the very least, the thing believed needs to be true, which is not typically something guaranteed by the physical state of the brain.

Many philosophers believe the dependence on states outside of the brain goes even further than that -- what it is you believe (and therefore know, when your belief is knowledge) is not just a matter of the physical state of your brain, but also the physical state of the world beyond your brain (again, typically). That view is called "externalism about content", and is maybe the most interesting insight of 20th century philosophy; I recommend you check out the literature on it.

  • Since most things past generations considered (sometimes rock-solid) "knowledge" were plain wrong, there is no reason but conceit to assume that our generation is different. Which implies that there is very little, if any, "truly true" knowledge, and, correspondingly, no necessity for anything outside the brain to correspond to it. Commented Mar 9 at 18:36

Good question, and one involving the problem of the universals. Ultimately, knowledge, if such a thing can exist at all, must involve intentionality, that is it must be about something. That means that when we know something, it must involve apprehension of the thing known. When I say "Fido is a Dog", I possess a proposition that is about Fido and about "Dogginess" and about Dogginess being true of Fido. Indeed, for this proposition to be true, it must be about something that actually is the case; as the saying goes, "veritas est adaequatio intellectus et rei": truth is the conformity of the intellect with the thing.

Now, how can this kind of intentionality take place? You mentioned physicalism, which is interesting, because intentionality, as as species of telos (aboutness is a species of directedness), is banned from physicalism as an assumed tenet. Indeed, this is one of the decisive blows against physicalism. Others are the so-called problem of qualia and the inability to account for subjective experience (taken to absurd lengths like eliminativism, i.e., the denial of subjective experience), as well as the existence of abstract concepts (take Triangularity as opposed to concrete triangles in the world; you never encounter the first, only the second, but the second are made intelligible by means of the first which are abstracted from those concrete instances).

So, I would say, knowledge is immaterial.


The knowledge argument is the formal way of wording your question that philosophers try to answer. TedEd has a really good video that can help you think about the answer to your question:

Is knowledge physical? Qualia and The Knowledge Argument

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    It is advised to supply links with a citation or your own explanation to avoid empty answers when those links die.
    – Johan
    Commented Mar 9 at 14:00

The term "knowledge" is used with a lot of different meanings. Here are the first two and main (according to me) definitions from Dictionary.com

1. Acquaintance with facts, truths, or principles, as from study or investigation; general erudition 2. Familiarity or conversance, as with a particular subject or branch of learning: A knowledge of accounting was necessary for the job.

(You can find the same essential descriptions from most dictionaries.)

Now, in philosophy in particular, we can consult its description by Stanford Encyclopedia of Philosophy (part of which are very similar to the above definitions):

"In introductory classes to epistemology, we are taught to distinguish between three different kinds of knowledge. The first kind is acquaintance knowledge: we know our mothers, our friends, our pets, etc., by being acquainted with them. The second kind is knowledge of facts, propositional knowledge, or knowledge-that: this is the sort of knowledge we acquire when we learn that, say, Ithaca is in New York State or that Turin is located in Italy. It is customary to add to the list a third kind of knowledge that is supposed to be distinct both from acquaintance knowledge and from propositional knowledge. One possesses this knowledge when one can be truly described as knowing how to do something: play the piano, make a pie, walk, speak, create, build, and so on."

In the third kind, we read the word "possess", which might allude to a physical possession only that is isn't.

If something is physical, it can be perceived with our bodily senses. Not only the 5 basic senses but with and of the about 50 senses that are known. E.g. sense of movement (kinesthetic), gravity, balance/equilibrium, orientation, etc.

So, the criterion for anything about whether it is physical or not, is "Can it perceived by our senses?"

If you apply this criterion to all the above mentioned definitions/descriptions of knowledge, you will easily conclude that it is not physical.

  • If something is physical, it can be perceived with our bodily senses - 1) what's the source of this definition? 2) we cannot perceive neutrinos with our bodily senses, therefore neutrinos are not physical?
    – Mark
    Commented Mar 9 at 22:59
  • First of all, my stetement about "senses" was not a definition. It was a logical argument that served my position. A short definition of the term "physical" is "something that is material". Now, about neutrinos and other particles: they are not visible to the naked eye. But they are visible using specialized instruments. See, they are still "perceivable".
    – Apostolos
    Commented Mar 10 at 7:59
  • Other counterexamples: 1) we cannot perceive other universes in the multiverse with our bodily senses (if a multiverse exists), therefore, other universes in the multiverse are not physical? 2) We cannot perceive dark matter with our bodily senses, therefore, dark matter is not physical?
    – Mark
    Commented Mar 10 at 13:46
  • Another problem: we can experience knowledge in our mind, therefore, we can perceive knowledge. Therefore, knowledge is physical?
    – Mark
    Commented Mar 10 at 13:49
  • Before continuing with other examples and problems: if you agree with my stement "If something is physical, it can be perceived with our bodily senses" --which I see that you didn't reject-- wouldn't you like to upvote my answer?
    – Apostolos
    Commented Mar 10 at 18:23

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