Is the non-physical amenable to research and investigation?

Question

Has philosophy proposed a sufficiently clear criterion for distinguishing the "physical" from the "non-physical" that would enable us to:

1. Identify aspects of reality that qualify as "non-physical," and, more importantly,
2. Develop methodologies for researching or investigating these "non-physical" aspects of reality?

In other words, have philosophical frameworks been proposed that enable both the identification and the investigation of non-physical aspects of reality, if such aspects exist?

By methodologies of investigation or research, I mean any procedures that could be followed by an individual to acquire knowledge or gain a deeper understanding of non-physical aspects of reality that the methodology is designed to explore or study. In that sense, is it even coherent to talk about researching something non-physical, or would this constitute a contradiction in terms?

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NOTE: While several questions have already been asked about defining terms like "physical," "non-physical," and "natural," none have focused specifically on whether the "non-physical" can be researched and, if so, how. Examples of such previous questions include:

• What is the definition of physical? Is that definition clear enough to make a distinction between physical and non-physical?
• How can something non-physical exist?
• What is the difference between Naturalism and Physicalism?
• Is physicalism an unfalsifiable position?
• Do non physical causes exist?

Answer 1

You ask:

Is the non-physical amenable to research and investigation?

Ceteris paribus, yes. Many non-physical phenomena are investigated. In the exotic cases for we secular physicalists, we have para-psychology or theological research where the supernatural is presumed to exist. Now, that being said, many who are militant against the supernatural will answer no, so in that vein, you'll find those here who will reject it based on their metaphysical framework; but this knee-jerk response is from those not aware of thir metaphysical biases. From a purely philosophical perspective, the non-physical can be investigated.

Even if you reject the supernatural, the formal sciences are largely taken not to be empirical disciplines primarily. Mathematics and logic is not about utterances and media; it's about ideas. A Platonist will certainly endorse the idea that mathematical objects, which are abstract objects can be investigated despite lacking a physical property. And you won't find many logicians who endorse the idea that propositions have some physical dimension. Ideas, concepts, and meanings are taken to be "above or over" the physical media that conveys them by many, and this bleeds into realist metaphysical positions.

You state:

By methodologies of investigation or research, I mean any procedures that could be followed by an individual to acquire knowledge or gain a deeper understanding of non-physical aspects of reality that the methodology is designed to explore or study.

Here, I'm concerned you are taking a woo-like approach to reality. There is physical reality built on causal closure and spatiotemporal extension, and putative abstractions and non-physical entities are attributed to it in various ways by various thinkers. In modern science, the chief methodology for investigating that without a physical basis is operationalization. Philosophically, the primary method is scientific in that is a form of scientific reduction (SEP). From the article:

Reductivists are generally realists about the reduced phenomena and their views are in that respect conservative. They are committed to the reality of the reducing base and thus to the reality of whatever reduces to that base. If thoughts reduce to brain states and if these brain states are real, then so too are thoughts. Though conservative realism is the norm, some reductionists take a more anti-realist view. In such cases the reducing phenomena are taken to replace the prior phenomena which are in turn eliminated. The idea of mental illness as a type of psycho-neural disorder replaced the idea of demon possession. Demons and their voices have no role or reality in the new theory. The oxygen theory of combustion replaced the phlogiston theory and phlogiston was eliminated.

So, when dealing with things that are outside the bounds of the physical, by setting up repeatable and measurable procedures helps us to determine theories to account for things that don't have directly obtainable empirical properties. Energy is a perfect example. Most physicists will tell you energy is physical, but something like potential energy doesn't actually have directly observable physical properties. This undermines realist arguments and is seized upon by instrumentalists to claim that the case made traditionally by scientific realists is overstated, and that observation and theory are interrelated as in the case of theory-ladenness. There's a gulf between the senses and the intellect created by the phenomenological perspective, and it's not quite so simple to bridge. Just look at the conceptual complexity of Kant's CPR!

Answer 2

If by non-physical, you mean something with no effects on the world, then no, it cannot be investigated.

If you include in the non-physical things that can have effects on the world, then yes, it can be investigated by observing and experimenting in relation to those purported effects.^*

And if you include in "investigation" simple reasoning within an axiomatic system, then even mathematics can be "investigated," regardless of whether one views mathematics as having effects on the world or not.

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^{* E.g. if one accepts the "metaphysical presupposition that the mental world affects the physical world," then under that assumption, the mental world can be investigated.}

Answer 3

It depends on what you mean by non physical. For example. some physicalists may categorize consciousness as supervening (depending) on the physical, but may still consider it valid to call consciousness “non physical”.

So let’s assume that by “physical” you mean anything that is or supervenes on the physical. If so, then the question now begs the further question of whether something non physical (excluding purely abstract objects) exists in the first place. Before even talking about whether we can investigate the non physical, we must first establish if it exists. And so far, this has simply not been done,.

So as of now, your question is meaningless.

Answer 4

A brief attempt to answer my own question, primarily building on Lowri's answer.

Case 1: Assuming the non-physical exists and humans have a dual physical/non-physical nature:

• Option 1: Non-physically studying the non-physical directly using the non-physical part of our nature. This approach sounds quite mystical and aligns with mystical religions or even occultism.
• Option 2: Physically studying the effects of the non-physical on the physical. This aligns with parapsychology, and potentially theology—if one assumes deities revealed theological knowledge that was physically recorded in texts. It might also align with mathematics, assuming the non-physical Platonic realm influences the physical in some way.

Case 2: Assuming the non-physical exists and humans have access only to physical means of investigation:

• Option 1: Ruled out by definition.
• Option 2: Remains a possibility.

Case 3: Assuming the non-physical does not exist:

• Option 1: Trivially ruled out.
• Option 2: Trivially ruled out.

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Addendum on mathematics

If a non-physical Platonic realm exists, if such a realm cannot causally affect the physical, then unless we possess a non-physical means of directly accessing it, whatever we are physically engaging with when we do mathematics—whether thinking mathematically with our brains, writing equations on paper, or using a computer—cannot be the actual mathematics of the Platonic realm, unless the two correspond purely by metaphysical luck. Related discussion: Since mathematicians are physical beings, does this mean that mathematics ultimately reduces to physics?