Awkwardly synthesizing jobermark's old question Is there a boundary on 'physical'? with my (badly put) question Can physics talk about non-physical entities/concepts, and if not which academic department does?, finally pinpointing (I hope) what bugs me.

Let me start with what I'm hoping to find:

  1. Non-physical having causal effects on the physical (and vice versa).

  2. Clear enough definition (no matter how general it is) of physicality that'll distinct between physical and non-physical, or, will provide boundaries of physicality.

  3. A definition of physicality that'll account for the history of physics, the changes on how we viewed physics and non-physics.

  4. Not a dualistic solution.

In jobermark's question he presents the idea that the definition of physicality is so vague that it always expands and encompass what was in the past not considered physical (similar, in general, to the vagueness of "the scientific method"). Then he goes to state that this makes the distinction between physical and non-physical as near non-existent nowadays*.

My question was about the academic scope of this question, as in, not only conceptually, but practically - is a physicist able to talk about the non-physicality. This question seems more clear to me after going through jobermark's because it means that the physicist, if he talks about non-physical entities, might not know that it's in fact what he does because to him it seems like physical entities (because of, again, the vagueness of the definitions).

So after pinpointing that the root of the issue was at the definition level (which I basically tried to ignore in my question), and where jobermark's answers weren't suffice (at the end I think he took a turn in his answer, which seems to me like a bit of avoiding the problem) because while admitting the problem they haven't really provided a concrete answer (maybe there isn't one, and if so this question can be deleted).

So, my question will be - is there any clear enough definition of physics that answer the 4 requirements I've stated above?

(*although there are the ways that's been shown in the answers to Alexander's question How can something non-physical exist?, the first positing the distinction in abstractness/concreteness but agrees to providing physicality all of the causal realm [which isn't what I'm seeking]; the second doesn't really distinct them but rather takes a sort of holistic/monistic approach, which isn't bad but doesn't yet answers the question to its full extent [even in this holistic approach one needs to distinct where the physical end and the non-physical starts]; and another answer distributes the physical and non-physical to different areas of existence, which [I think] renders every attempt to bring non-physical causality to science as futile)

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    Possible duplicate of What does "physical" mean to philosophers?
    – Conifold
    Commented Mar 20, 2018 at 17:49
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    @Conifold thanks, it is similar (although I pinpointed the answer more on the boundaries and the distinction between the physical and the non-physical, which is a bit more accurate than a general definition). But the answers to that question seems like what jobermark was complaining about in his question- almost all the answers say that either physical is undefined or that it'll simply encompass everything that can be studied in the natural science. In this way, there's no actual point in talking about ideals (non-subjective), because if they'll turn out to be real they'll be called physical. Commented Mar 20, 2018 at 18:31
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    Everything that can be studied in natural (or any) science is not everything, art and ethics have different purposes, for example, and ideals are typically studied in ethics. And even if everything science studies will be declared "physical" the point is to describe more precisely what it is and how it behaves, so I do not see a problem. As long as we do not yet have the full picture for the objective ideals, if any, what difference does it make if they will eventually be called "physical" or not?
    – Conifold
    Commented Mar 20, 2018 at 19:40
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    @Conifold I'm not talking about those different sciences. And there's no real problem with calling those phenomenons physical, it just seems that the linguistics can easily confuse, so much that we simply don't know what we're talking about when we're distinguishing between physical and non-physical. We can go ahead and call seemingly mental activities physical, but that's not what we mean when we say those two different words right? Commented Mar 20, 2018 at 20:11
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    You seem to be making a rookie mistake that one needs a "proper definition" of X to talk about X: we do not need to know lines, nor should we care. "Definition" comes at the end of inquiry, not at its beginning, and we definitely do not need any "clear" mental/physical distinction, nor are we anywhere near giving a useful one (it is similar with living/inanimate). No "valuable information" will be lost on behalf of it because vagueness excludes little ("treating as physical" does not attach to any "set of rules"), it is distinctions, especially "clear" ones, that restrict options prematurely.
    – Conifold
    Commented Mar 20, 2018 at 21:50

3 Answers 3


Its a conceptual distinction to understand our experience. Theres only experience, but we categorize it to understand it. Einstein said:

"A basic conceptual distinction, which is a necessary prerequisite of scientific and prescientific thinking, is the distinction between “sense-impressions” (and the recollection of such) on the one hand and mere ideas on the other. There is no such thing as a conceptual definition of this distinction (aside from circular definitions, i.e., of such as make a hidden use of the object to be defined). Nor can it be maintained that at the base of this distinction there is a type of evidence, such as underlies, for example, the distinction between red and blue. Yet, one needs this distinction in order to be able to overcome solipsism. Solution: we shall make use of this distinction unconcerned with the reproach that, in doing so, we are guilty of the metaphysical “original sin.” We regard the distinction as a category which we use in order that we might the better find our way in the world of immediate sensations. The “sense” and the justification of this distinction lies simply in this achievement. But this is only a first step. We represent the sense-impressions as conditioned by an “objective” and by a “subjective” factor. For this conceptual distinction there also is no logical-philosophical justification. But if we reject it, we cannot escape solipsism. It is also the presupposition of every kind of physical thinking. Here too, the only justification lies in its usefulness. We are here concerned with “categories” or schemes of thought, the selection of which is, in principle, entirely open to us and whose qualification can only be judged by the degree to which its use contributes to making the totality of the contents of consciousness “intelligible.” The above mentioned “objective factor” is the totality of such concepts and conceptual relations as are thought of as independent of experience, viz., of perceptions. So long as we move within the thus programmatically fixed sphere of thought we are thinking physically. Insofar as physical thinking justifies itself, in the more than once indicated sense, by its ability to grasp experiences intellectually, we regard it as “knowledge of the real.” After what has been said, the “real” in physics is to be taken as a type of program, to which we are, however, not forced to cling a priori." A. Einstein, “Remarks concerning the essays brought together in this co-operative volume,” in Albert Einstein: Philosopher-Scientist, P. A. Schilpp, ed., pp. 665–88. Tudor Publishing Co., New York, 1949

For me we can talk about interior experiences, and external (physical) ones. The internal world acts on the external one all the time.

  • Good point. Pragmatically, we experience reasoning, logic, causation, and qualia experiences. None of these are demosntrated to be reducible to the physical, and there isn't even a plausible program to do so. To think, or do anything, we must pragmaticaly use experience, and reasoning. IE, even physicalists must work off non-physicalist starting assumptions. Pragmatically, we are forced to reject physicalism from the get go.
    – Dcleve
    Commented Dec 16, 2018 at 18:25

Aristotle invented the word τὰ ϕυσικά ("ta physika," lit. "natural things"), which is the collective title of his physical treatises. Natura comes from natio = birth, so natural [or physical] things are generated, the product of a change.


  • So static physics study isn't really physics? Or it is if you assume they came from a dynamic state? Commented Mar 21, 2018 at 10:06
  • @YechiamWeiss Statics studies the same changeable objects that dynamics studies.
    – Geremia
    Commented Mar 21, 2018 at 16:02

In answering your headline question

What is the definition of physical?

I propose the following working definition: A phenomenon is physical if it can be investigated by the physical method. The latter is a synthesis of

  • Observation
  • Theory
  • Checking theory against observation.

I try to satisfy your requirements 2) - 4). But I do not understand your point 1). What is the requirement here?

Added: This working definition classifies the following issues named in the OP's comment:

  • What makes up the mind: Neuroscicence investigates the neuronal substrate of mental processes. Hence these investigations deal with physical phenomena.
  • Qualia. I take qualia = felt qualities. I consider these subjective phenomena on the border between physical and non-physical phenomena. E.g., the experience of colours is a physical phenomena, starting with investigating the principles underlying the cones in the retina.
  • A type of basically unobservable substance suggested in different interpretations of panpsychism: Apparently non-physical.
  • Understandably, because your definition would include those "non-physical" entities. This would also (correct me if I'm wrong) entail physicalism, at least on the point of what can be studied as a natural phenomenon. I might need to include that in my question (requirement for non-physicalistic definition). Sorry if I'm somewhat vague here. Commented Mar 21, 2018 at 16:10
  • Please name some phenomena you consider non-physical. Possibly we can then decide whether they fall under my working definition or not.
    – Jo Wehler
    Commented Mar 21, 2018 at 16:13
  • What is considered under the realm of "idealism", in the broad sense that includes objective idealism. An example for a phenomena under this realm may be part of what makes up the mind, or what is considered "qualia", or a type of basically unobservable substance suggested in different interpretations of panpsychism. Commented Mar 21, 2018 at 16:17
  • The method of observation, hypothesis, test, revise -- is not limited to the physical. Scientists have historically applied this method, and reached a variety of physical, dual, and idealsit ontologies as an outcome. Your proposed boundary does not seem to work.
    – Dcleve
    Commented Dec 15, 2018 at 17:33
  • @Dcleve could you please give an example of, say, idealist ontology as an outcome of this method? Commented Dec 15, 2018 at 17:52

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