Do Contradictory Descriptions of Reality Mean that None of Them are True?

Seemingly conflicting or inconsistent descriptions of reality might make one think that we really aren't seeing the world as it is, but as we want to see it. Or are we seeing it through whatever current cultural/historical/political filters we have constructed, or through neurological/physical filters we are born with? I don't think this is correct, in that I don't think the statement "seeing the world as it is" is really a meaningful phrase. I think it is probably synonymous with "seeing ultimate reality", which is another very poetic, mystical, and dazzlingly non-specific expression. Both phrases imply (without any explicit justification) that the world is some other unspecified thing than what we see. No doubt we each perceive political and social events through personal filters (in that we interpret the same actions differently), but we are all still "seeing" the same physical events happening - the same photons are entering our eyes, the same sound waves are entering our ears, the same sensory nerve endings on our fingertips are being stimulated, and the same sensory neural pathways are engaged. As to whether we experience the same "qualia" (i.e., subjective experience of those sensory inputs), that is another question altogether, not considered here. Unless evidence is presented to believe that qualia is different, I will proceed as if our separate personal experiences are more or less the same, in the same way that we each digest food in the same way, we each react to an alarm in the same way, and we each get hungry in the same way. There is no indication that mental/brain functions differ substantially among individuals any more than these other body functions.

Considering that there is no reason to think otherwise (i.e., evidence to the contrary does not exist) the most parsimonious assumption is that we are seeing what is really there, even if what we see is an incomplete or partial picture, limited by our sensory organs and cognitive abilities. And yes, technically it is correct that we are experiencing observable "phenomena" rather than Kant's "thing in itself" (the "noumena"), but what alternative is there? That is the nature of, and the definition of, perception. I would not call that a limitation, I would call that the way things work.

That we experience an external reality called "the world", I think, is indisputable. Rather, I should say, as a Philosophical Realist, if someone is in the mood to dispute it, it will have to be with someone other than me. That particular debate quickly devolves into pointless speculation. It is not that there is any particular evidence against this kind of Subjective Idealism or other form of Anti-Realism, but that no evidence could possibly bear on it at all, since any real-world evidence would immediately beg the question of real-world existence. That makes the topic uninteresting. And it is pointless because both sides reach stalemate after the first move, short-circuiting any hope of making intellectual progress. So there is no reason to even have the discussion. In any case, there are no compelling reasons to disbelieve external reality, and plenty of reasons to believe it (though I will admit that no deductive proof of it is possible - see here for more). No acceptable competing explanation has been proposed for our experiences in the world. This doesn’t constitute irrefutable proof, instead utilizing “inference to the best explanation”, meaning that among the only set of available explanations, Realism is by far the strongest. Further, Realism is also the only theory which aligns with the proposition made by Hilary Putnam - the "No Miracles Argument", which is “The positive argument for realism is that it is the only philosophy that doesn't make the success of science a miracle”. All other explanations are highly ad-hoc and rely on a steady stream of miracles for them to be correct.

Given that we are actually perceiving something outside ourselves, we do our best to describe it and understand what we are seeing, experiencing, and measuring. Our descriptions reflect the models of reality that we currently subscribe to. Science, which originates the more quantitative and formal versions of these descriptions, does not attempt to provide a perfect representation of reality, but one that "works". The models of science describe with some level of approximation what is being studied, and they "adequately" explain what is going on, allowing us to predict what we are likely to see concerning a particular phenomenon in the future.

In our everyday lives, the less formal models we form of the world (e.g., the mental map we make of a route to a destination, the recipe for a meal) are also stylized, abbreviated, and intentionally incomplete. We do not attempt to, nor can we succeed at making a model that fully encapsulates the reality it is describing.

The primitive, pre-scientific, model of a sun and moon that actually rose and set in the sky had some basic predictive power (you could be sure that every 24 hours the sun would come up). As a model of reality, it provided some descriptive and predictive value, but overall was not very powerful. Its chief weakness was that it did not correspond to the actual mechanical motions of the celestial bodies - it didn't mirror or take into account the actual paths of the celestial bodies. It predicted the right outcomes (sunrises) for the wrong reasons. The more sophisticated Ptolemaic solar system also was a model of the sun and its planets that worked reasonably well at predicting planetary motion. But again, it failed even to approximate the motions of the bodies in the solar system. A better system (more accurate and "truer" as per the "Correspondence Theory of Truth") was the heliocentric model introduced by Copernicus. It was truer in that it bore a closer relationship to the actual structure of the solar system than Ptolemy's model - its level of "correspondence" to the physical reality it described was higher. At least it acknowledged the roughly circular motion of the planets, and put the Sun in the right spot. But even Copernicus' heliocentric model had problems resulting from his dogmatic commitment to perfect geometric forms - he was convinced that the orbits had to be perfect circles, which they aren't. Kepler corrected this error by showing that the orbits were actually ellipses. But Kepler had his own ideological biases. He wanted to fit the five Platonic solids inside each other, wrap them in nested spheres, producing six concentric layers corresponding to the orbits of the six known planets — Mercury, Venus, Earth, Mars, Jupiter, and Saturn. This conceptually attractive ideological position was also was incorrect. Eventually, astronomers who came after Kepler refined our understanding of planetary orbits to the highest level of detail we could achieve using classical Newtonian mechanics. However, in the 20th century, we saw that the orbit of Mercury was different than had been predicted by classical mechanics due to relativistic effects ("frame dragging"). The orbits, once again, had to be refined to take relativity into account.

Does this constant abandonment and/or refinement of old models mean that we don't know, or can't know reality? Not at all! It only means that our mental and mathematical models of reality improve over time, and come closer and closer to approximating what is really going on. We are living through this today with constantly evolving climate models that try to predict global warming. Descriptions are not the same as the reality they describe, but only "point" to that reality. They are references with built-in limits. Not insignificantly, they also can reflect our human bias and preference for finding a single cause or explanation of a set of phenomena that are, by nature, multifaceted and not reducible to one description. Most importantly, models are abstractions and simplifications, and they necessarily filter out and lose some of the detailed richness which exists only in the reality they refer to.

Not all philosophers have even this level of trust in our ability to model reality. Wittgenstein said that we humans cannot experience "ultimate reality" (whatever that means!), but only can create a language that "points" to reality. He is highly critical of scientific explanations, saying that not only do they fail to approximate "reality", but that they only have value in supporting each other. According to him, our laws of nature cast the form that any description of the world must take. They tell us nothing about the world, itself. We can infer some things about the world from the fact that it is more easily described by one explanatory system than another. But we are forever separate from direct experience of it. Wittgenstein's view, however, is not currently "in vogue" with philosophers of science. But it is one dissenting voice.

Some people dispute the assertion that our perceptions and descriptions mirror reality, that they have a "high correspondence" with reality, high enough to say that we can "see reality as it really is". They say that our view of reality is an illusion, a misleading and false image. If they are invoking solipsism, subjective idealism, monism, or some other view that denies an external reality, then let's stop the discussion here. As I have described here, here, here, and here, these are philosophical dead ends, and I have no interest in pursuing them. However, if the dispute relates to our limited human ability to perceive "things in themselves" correctly, or if the question of the meaning of "things in themselves" is interesting, we can continue. Let's look at this using the example of the ostensibly "solid" kitchen table. What appears to be solid is really an object composed mostly of empty space sparsely populated with atoms. Even the atoms, themselves, are mostly empty - nuclei surrounded by distant electrons. The nuclei of those atoms are made of protons and neutrons, which are, in turn, made of quarks and gluons. Some physicists now think that the subatomic particles (quarks, electrons, neutrinos, etc) are themselves manifestations of interacting fields and are not "solid" in the sense that we typically think of that word. And Sean Carrol has written that at a level "under" that, the universe is nothing but a Hilbert Space with a single wave function describing all of reality, and that it has a Hamiltonian that describes the evolution of that wave function (but of what use is that?).

So is the table solid, or is it made of scattered particles, or is it not really made of anything at all? I think that it is correct to think of matter as solid, and to also think of it as mostly empty space, and to think of it as energy, and to think of it as many (or possibly just one) wave function. It is all these things simultaneously. It all depends on the scale of our observations, and the purpose for which we are keeping track of the experience. If you are looking at the table as particles and their interactions, it is not going to tell you much about how to lay out silverware or who should sit next to Aunt Martha. If you look at it at the level of serving Thanksgiving dinner, it is not going to inform you about how matter interacts and is structured. Massimo Pigliucci stated this well:

"Let’s pursue this illusion thing a bit further. Sometimes people also argue that physics tells us that the way we perceive the world is also an illusion. After all, apparently solid objects like tables are made of quarks and the forces that bind them together, and since that’s the fundamental level of reality (well, unless you accept string theory) then clearly our senses are mistaken.

But our senses are not mistaken at all, they simply function at the (biologically) appropriate level of perception of reality. We are macroscopic objects and need to navigate the world as such. It would be highly inconvenient if we could somehow perceive quantum level phenomena directly, and in a very strong sense the solidity of a table is not an illusion at all. It is rather an emergent property of matter that our evolved senses exploit to allow us to sit down and have a nice meal at that table without worrying about the zillions of subnuclear interactions going on about it all the time."

Or as Robert W. Batterman wrote:

“The idea being that a phenomenon is emergent if its behavior is not reducible to some sort of sum of the behaviors of its parts, if its behavior is not predictable given full knowledge of the behaviors of its parts, and if it is somehow new — most typically this is taken to mean that emergent phenomenon displays causal powers not displayed by any of its parts.”

This is not magic, but an expected property of complex systems. Its opposite - the ability to anticipate all higher level behaviors from primitive parts is what would be surprising - to be able to describe a carburetor by examining its springs, screws, and gaskets would be completely unexpected.

No one description will give you all you want or need when you are trying to "explain" the world. Although it may be logically possible to eventually come up with a quantum theory of dinner, we probably aren't going to see any such theory soon. It would not really be useful, in the same way that planning a summer vacation road trip by examining and evaluating every millimeter of highway that you intend to travel would not be useful. The different levels that we model and describe the world assist us to understand it at that level. They are human-created tools that are meant to increase our human understanding. They are not models given to us by the universe we are trying to explain. It is possible to be a materialist, as I am, and believe that the universe is made of "stuff" that obeys the laws of physics, and also understand that this "stuff" interacts and merges in very interesting ways that exhibit increasingly complicated properties and behaviors as its complexity grows. As complex systems and entities come into being through the interactions of their constituent pieces, higher level descriptions and explanations also become more useful. One of the most well known examples is that of statistical mechanics (a mathematical system that applies statistical methods and probability theory to large assemblies of microscopic entities). It is far better at explaining how air moves in a room than any description that involved examining and itemizing each air molecule in the room. This concept applies to most, if not all, complex systems.

So-called "solid" matter is a network of atoms bound together with electromagnetic force. At the atomic level, matter is a sparse field of distant particles. But at a macro level, it is impenetrable to other objects also made out of matter. At the subatomic level inside atoms, the individual elementary particles are not "things" at all, as we think of material objects. They are entities with properties like spin, charge, mass, color, and flavor (to borrow some terminology from quantum physics). It is not clear at all whether these properties that we measure actually correspond to a "thing", or if the properties and their interactions are what constitute reality. This gets into the realist/anti-realist debate. It is not a new concept to think of objects at this level as not objects at all, but "fields" (Michael Faraday first proposed this back in the 1800's). At deeper and deeper levels, we see one layer of "structure" inside another. It may well be that at these quantum levels, reality is nothing but "structured information" all the way down, with nothing resembling what we would call "matter" at the bottom (See James Ladyman: Every Thing Must Go and Max Tegmark Our Mathematical Universe). At this low level, matter itself may dissolve into nothing but information, properties, and relationships of properties. Quantum particles, the ultimate constituents of matter (as far as we know) may be nothing but collections of mathematical properties. For example, the electron has the quantum properties of mass, charge, and spin, and a wave property called its "wave function". That is all - those properties do not decompose into more fundamental measures. In its relation to an atomic nucleus, an electron can occupy an atomic orbital, and when other subatomic particles with their own properties come together, new properties of the components and their relationships emerge. So, in some sense, our intuitive belief that real objects exist "all the way down" may turn out not to be true. But at the higher level of our normal human perception, they certainly do exist.

The idea that underlying reality is pure information, structure, and mathematical properties is part of the philosophic view of "Ontic Structural Realism", which is gaining some support in recent years. This theory states that underlying the most basic of objects - subatomic particles, there exists nothing but mathematical properties and structural relationships between properties that themselves are incapable of further reduction. They are the primitives from which the universe is constructed. They would represent the "foundation" of Foundationalism. According to this view, our best theories in physics do not describe the actual nature of things, but the structure of reality. We should not insist that the nature of the unobservable objects that cause the phenomena we observe is correctly described by our best theories. However, neither should we be anti-realists about science. Rather, we should adopt structural realism and only commit ourselves only to the mathematical or structural content of our theories. This "Epistemic Structural Realism" focuses on what we can know, rather than what actually is underlying what we know.

This allows retention of our structural understanding even as our theories change, augment each other, and even sometimes replace each other. So, Einstein's theory of gravity does not "cancel out" Newton's theory, but alters the understanding of the underlying structure referred to by both theories, which doesn't change. The same would be true of any future Quantum theory of gravity to General Relativity theory. The underlying structural reality of a phenomenon called "gravity" still exists. Our theories and models change and are refined or even revolutionized, but the structural aspects of the reality they describe remains intact. The same could be said of many theories that, over time, have required significant revision or replacement. For example the Thermodynamic/Kinetic theory of heat exchange replaced the Caloric theory, or Lavosier's oxygen theory of combustion replaced the phlogiston theory, and there have been numerous models of the atom over time. Despite the changes to, or even replacement of, those models and theories, the underlying structure representing "heat" and "atoms" persisted. A simple statement of Epistemic Structural Realism is that all we "know" of reality is the structure of the relations between things and not the things themselves. A correspondingly rough statement of Ontic Structural Realism is that there are no "things" at all (at least at the lowest levels) and that structure and relationships between structures is all there is. This is very non-intuitive for a macro-level being. However, that should not be a problem for someone wanting to use the table simply to serve breakfast on, which is how most of us use tables.

It was very likely surprising for our ancestors to discover that supposedly solid matter was a thin collection of atoms interacting with each other from a distance. So what? Whether we like it or not, that is just how matter works, regardless of any pre-scientific opinions we may have harbored (or still harbor) about it before the discovery of atomic and chemical interactions. No doubt it went against conventional "common sense" for this to be the case. Much of what we have learned in science disturbs our complacency - that is the nature of scientific discovery. It certainly went against what seemed to be the case to learn that white light was actually composed of a rainbow of colors, that continents floated on Earth's mantle like bars of ivory soap in a bath tub, that the Earth was not the center of the universe, that space was curved, that simultaneous events were not simultaneous at all, that there were living organisms too small for the eye to see, and so on. Just because new knowledge is intuitively disturbing or (seemingly) illogical, we must defer to what the universe is actually doing rather than what we would prefer it to do. And if it seems to offend our sense of what is and is not possible, so much the worse for our preconceptions. It is wise, humble, and properly respectful to allow Nature and Reality to instruct us, rather than to arrogantly impose our ill-informed, human-centric biases on it.

The view we have of reality (of real objects) depends on our perspective. We know that at a quantum level, objects have one set of characteristics, at an atomic and molecular level a different set, and at a visible macro level, yet another set. The salient characteristics that you focus on at any particular time depend on what use you are making of that object. Our view of reality is not purely objective - we are motivated to describe it in terms that will help us interact with it or understand it in some self-interested way. We describe reality with our models, but our models are not exact mirrors of that reality - they are "approximate" mirrors that only are "provisionally" true (true until proven otherwise), and valuable only to the extent that they help us achieve our goals. If you need a place to set your coffee cup, a wooden table can be regarded as a solid, flat piece of material. If you are a woodworker, suddenly the grain of the wood becomes interesting. If you are a botanist, the individual plant cells in the wood take focus. A structural engineer would see it as the solution to a load-bearing problem, a chemist might be interested in the structure of its cellulose, and a physicist could lecture us on what is going on inside the atoms, etc. The table is all these things. These different perspectives don't contradict each other - they enhance each other. They just describe the same object in different, complementary ways. Each new description deepens and enriches our understanding of the table, rather than muddying it. Choosing among them allows us to focus on the aspects of reality that matter to us at the present moment.

James Ladyman, in his 2013 book Every Thing Must Go (mentioned above), discussed this issue. He proposed that at the level of experience which human beings usually operate, the patterns we perceive really are those of a table. It makes sense to call the pattern we experience in daily living a table because it stable enough in space and time at that level that, for our purposes, it is a table. At the atomic level, you can't say that the table is "really" made of protons, neutrons, etc, because those things are patterns that instantiate yet a more fundamental understanding of reality, which is that they are not made of "things" at all, but interactions of different types of quantum fields. What it means to say, "there really is a table", is that we can be descriptively, predicatively, and explanatorily successful in our dealings with the world by taking there to be an enduring physical object with a certain mass and certain dimensions. Conceiving of that pattern as a conventional table will enable us to keep track of the phenomena and to make predictions, serve dinner on it, and so on. That is the scale of description that we are mostly interested in. At the more fundamental scale of description, not only is it that the alleged particles themselves are made of something else, but rather at this level the table doesn't really exist. Its boundaries give out. At a low enough level, it's not "useful" to track the phenomenon as a table at all.

Relax the burden of deductive proof

So, as shown in the previous section, we can't use deductive reasoning and pure logic (a priori) to prove the existence of "noumena" or "things in themselves" in an external reality. Most philosophers start off with the premise that they exist, and then focus more on our ability to experience them. This is descriptive of Kant, who spent much of his effort exploring how we only have access to noumena through the "phenomena" presented to us through our senses. For him, and for others, the question of the independent status of the noumena was not nearly as interesting a problem. He assumed that the noumenal world existed, but was completely unknowable to humans.

"Though we cannot know these objects as "things-in-themselves" (i.e., noumena), we must yet be in a position at least to think them as things in themselves; otherwise we should be landed in the absurd conclusion that there can be appearance without anything that appears."

He conceded, as did Scottish 18th century philosopher David Hume and others that:

"the reality of external objects does not admit of strict proof."

But that is exactly what we are talking about here. We are considering whether the noumenal world does or does not really exist - is there something behind the phenomena that we experience? As suggested previously, a significant problem is the application of deductive reasoning to the question. We should admit and concede that using the strict rules required for deductive logic can’t be applied to questions of this sort, nor can a priori reasoning be applied to the entire process of Inductive reasoning (you can't deduce that induction is a valid way to reason). Or, as Hume also said, in Dialogues Concerning Natural Religion:

...there is an evident absurdity in pretending to demonstrate a matter of fact, or to prove it by any arguments a priori. Nothing is demonstrable, unless the contrary implies a contradiction. Nothing, that is distinctly conceivable, implies a contradiction. Whatever we conceive as existent, we can also conceive as non-existent. There is no being, therefore, whose non-existence implies a contradiction. Consequently there is no being, whose existence is demonstrable.

Induction (proceeding from the specific to the general - as in "the sun has come up every day, so it will continue to come up) is a fundamentally different and looser form of reasoning than deduction. The truth-preserving nature of deductive reasoning doesn’t work when used to justify a reasoning process in which the conclusions are, by definition, not certain. The conclusions of inductive arguments exceed the content of their premises – individual cases when used to construct a general rule necessarily go beyond themselves. However, with deductive arguments the premises contain everything necessary to systematically arrive at a definitive conclusion – the conclusion is inescapable. For this reason, it is simply impossible and inappropriate to impose the tough standards of deduction on the fuzzier process of inductive logic, so we are left with inductive logic to "prove" the existence of a physical universe.

As we have seen, inability to disprove a proposition does not render it true. For example:

• Although the Omphalos and Solipsistic positions are immune to disproof, all reasonable people agree they are beneath consideration, mere philosophical novelties and parlor tricks.
• Russell's celestial teapot and the Flying Spaghetti Monster (blessed be his name) cannot be successfully defeated through argument. But, all satire aside, they are not really out there.
• The many varieties of supernatural mythologies all create beings or histories or forces that are beyond the means of science to disprove. This doesn't make them real.
• There is an astronomical number of other incredible claims that bear similar logical structures to the above examples that also are unsusceptible to the power of logic. They are not, therefore, all true.
• Likewise, no one can disprove this claim: "Reliance on induction is unwarranted". That does not automatically render this proposition true. If we can't disprove that "induction is groundless", reliance on induction is not, therefore, groundless. In fact, it is "probably true".

All assertions about the existence or lack of existence of the external world are beyond positive proof.

Problems with the use of deduction in discussing the existence of reality

If someone asks you to prove that reality exists, they are probably have in mind a deductive proof involving some sort of syllogism or other combination of premises and propositions, that lead to an inescapable conclusion. They are implicitly asking for a valid and sound analytical, logical proof. In propositional logic using deduction, if the premises lead to the conclusion, if the terms are clear and unambiguous, if all premises are true, and the rules of logic are followed, then the conclusion reached is necessarily true - we say that the conclusion entails the premises. In my past discussions with "reality-skeptics", no vague expressions of likelihood or probability were enough for them - they wanted a rock solid proof which only deductive processes can supply.

In other words, they are challenging you to come up with an "All men are mortal / Socrates is a man / Therefore Socrates is mortal" style of proof. If they are looking for something of this form (e.g., Premise A, Premise B, Premise C, Therefore reality exists), that's just not going to happen. Why? Because each of the premises will be taken from Reality, but Reality is the conclusion we are trying to prove, so this would result in circular reasoning, or "begging the question". If the argument is a variant of "I see the table, you see the table, therefore the table exists", both premises already assume that there is something to see and something to do the seeing, which is what the conclusion asserts - thus, circular reasoning. The only deductive argument in which "Reality exists" can play a role is as one of the premises, one of the unproven assertions that has to be taken as a given, not the conclusion. As to whether this would form a valid argument, it would depend on its logical structure (does the conclusion follow from the premises?). As to whether it is a sound argument, this would require that the premises be true, in the case of reality - can we assume or use inference to convince ourselves that reality exists? So, deduction is just not going to work if someone is asking for a proof. Its existence would be one of the premises.

Deduction is not the appropriate form of logic to use for questions involving existence in the real world. As David Hume wrote in Dialogues Concerning Natural Religion, nothing can be proven to exist using only a priori (purely logical) reasoning. You could only prove this type of existence if its opposite (non-existence) generated a contradiction (i.e., contradicted its premises, which it doesn't). It is not contradictory to assert we are all inside a giant simulation or dream. To assert that nothing is real is just as viable as its opposite. For example, you can't prove that there is a person standing behind you by showing that it is inconceivable that there is not a person standing behind you. We obviously can imagine that there is no person standing behind you right now (their non existence does not cause a logical contradiction). The only way to prove that a person is standing behind you is through evidence. And the only way to prove this is to turn around and look - to collect the evidence.

Solid proofs and deductive reasoning are applicable primarily in highly controlled scenarios such as in deriving and proving mathematical theorems, formal and symbolic logic, and in applied areas of technology such as software and circuit design - all areas where the conclusion is completely contained in the premises, and the premises are totally clear, unambiguous, and universally agreed to. In other words, it works best in extremely constrained and "clean" scenarios. Math and logic, though they lend themselves to the deductive proof, don't reveal truths about the actual world. Instead, they reveal consequences of axioms and premises. They start with an axiomatic structure and set of rules, and from those building blocks, theorems can be derived. They don't tell us which of the axioms are actually true. For that you need to go into the real world and look around.

Requiring deductive proofs, and expecting formal/propositional/deductive logic to always be applicable, puts an undue burden on deductive logic, asking it to do something for which it was not designed. For example, you can't prove deductively that chocolate is your favorite food, or that you are still employed at your job, or that a dropped ball will fall to the ground, or that the sun will rise tomorrow, or that an action you performed was generous and kind, or that a piece of art is good. Those issues, which are really very important (you don't want a dropped ball hitting you under the chin) are not settled by deductive proofs anyway. Humans do not use deduction in their everyday lives all that much. We infer things based on past experience, perceived likelihood of outcomes, elimination of unlikely scenarios (inference to the best explanation), and a learned set of habits about how to move through the world we find ourselves in.

Even more intriguing, you can't prove the deductive method actually works without enlisting the use of deduction. If someone rejects deductive logic, you can't insist that they believe it because it would be illogical for them not to. The logic that you are employing in your argument is the very thing they doubt in the first place. So, to insist that the legitimacy of our use of inference come along with a solid proof which does not involve inference is something that the other primary form of logical inference cannot even provide.

Although I can't come up with a deductive proof that reality exists, I can use the well known modus tollens argument (also known as denying the consequent or contrapositve) showing that deduction cannot be used! This logical form is:

• If P, then Q.
• Not Q.
• Therefore not P.

as in:

• If (P) it is raining, then (Q) the sidewalks are wet.
• The sidewalks are not wet (not Q).
• Therefore (not P) it is not raining.

Applied to the possibility of a deductive proof of reality's existance:

• If (P) there were a clear, ironclad deductive proof of reality, then (Q) we would not still be arguing about it.
• We are still arguing about it (not Q).
• Therefore (not P) there is not a clear, ironclad deductive proof of reality.

Again, using the argument form of “denying the consequent” we can offer a positive deductive proof that viewing the external world as really being there is correct. The argument that "We can rely on empirical and naturalistic evidence to learn about the external world" follows:

• If (P) "using naturalism and induction from sense experience to make inferences about the world is invalid and unjustifiable", then (Q) "science (which relies on inference and naturalism) has no hope of working".
• Science does work (not Q)! There are countless examples of the progress that it has introduced, discoveries that it has made, and new technologies it has spawned. There are no counter examples to its success during the centuries it has been practiced.
• Therefore, (not P) "using naturalism and induction from sense experience to make inferences about the world is invalid and unjustifiable" is FALSE. We CAN use naturalism and induction to make inferences about the world.

So, this argument would seem to prove that the external world really is there (using deduction to prove induction about the real world is a valid way of interacting with the world. But there are objections - no matter how far fetched. The hyper-religious could counter that this is all a deception by the Devil, or that it is a test by God to exercise our faith. Or the Solipsist might say we are dreaming the whole thing. The fact is - they are technically right - we can't prove they are wrong. But I would say, "so what?". Realists need not be concerned with it. Nature and the external world do not demand a proof - those are only requested by some people, and probably for reasons they would have a hard time justifying. And for those who consider themselves to be pragmatists - they don't care about "proofs" of the external world at all. The pragmatist employs what is useful, and discards the rest. Metaphysical proofs can be left to the others.

In any case, the type of reasoning called propositional logic (along with deduction and induction) was invented in Classical Greece and integrated into a system of thought by Aristotle. It uses deduction from premises to draw conclusions. He intended it as a tool for finding truth, but it didn't keep him from making many outrageous errors. His armchair deductions about the nature of the world were frequently wrong (the behavior of falling bodies, that flies had four legs, thought mucus was brains leaking out of our noses, he deduced five elements, that women have fewer teeth than men, and more). Although he contributed greatly to our understanding of the natural world (he invented the core of western logic and gave shape to several of the basic sciences we still practice today), he made a number of errors by misapplying the powerful tool of logic. Any tool can be misused, and in these pre-scientific days logic was misused repeatedly (and it continues to be misused today).

Aristotle understood that logic can be used to deduce true consequences from true premises. His technique has been much abused over the years. Many who have followed him failed to realize that we have usually have no absolutely true premises, except ones we define to be true (such as "2+2=4", or "no geese are felines"). There are no handy, obviously true premises about the existence of an external reality that we can bring to bear in formal deductive logic.

I have seen so many seemingly plausible attempts at the use of deductive proofs to prove the existence of god and other hypothetical entities that I have lost confidence in the entire endeavor (for a great example, see Anselm's ontological proof of god). The laws of logic do work, but it is not magic. You have to frame the premises correctly, and they have to be true. We say many things about the world that seem true on the surface, but may, in fact, lack meaning or be incorrect. Wittgenstein, in his Philosophical Investigations, wrote that conceptual confusions involving our use of language are the cause of many problems in philosophy. Clearing up the errors in language can make entire philosohical questions just disappear:

“Philosophy is a battle against the bewitchment of our intelligence by means of language”.

and:

"Most of the propositions and questions to be found in philosophical works are not false, but nonsensical. Consequently we cannot give any answer to questions of this kind, but can only point out that they are nonsensical … it is not surprising that the deepest problems are in fact not problems at all”.

Put another way, much of what is debated in philosophical terms is nothing but impressive, but empty, verbal gymnastics. For example, when arguing about "existence" I am not convinced we have a coherent, single interpretation of that concept. Prior to Kant, many philosophers thought "existence" was a property that objects either had (i.e., they were concrete things) or lacked (i.e., they were abstract things). Anselm, in his ontological argument, made this error. Kant demonstrated that "existence" is not a property like color or weight, but is "prepossessed" by the object, making it capable of having any properties at all. So, I am not at all convinced that the discussions that we amateurs and dilettantes have about existence are really doing anything but creating a lot of noise and muddying up the water. Even the professionals are not of one mind concerning this question.

Agreement on basic concepts is a prerequisite for discussion

For people to have a useful, meaningful discussion about philosophical issues, it is critically important that they adopt a common framework for that discussion. Otherwise they will end up just talking past each other, hearing each other's words, but not comprehending. When we each employ our own vocabulary, and don't use a common toolbox of concepts, both parties to a conversation are just engaging in separate monologs. It becomes impossible to have a useful exchange of ideas if the speakers can't come to a basic agreement on some the underlying terminology, assumptions, premises, and rules for discussion. They don't need to agree on the conclusions, but they must at least agree about what they are discussing!

Consequently, this requires a minimal acceptance of some basic basic rules of logic. A common understanding of basic terms must be reached if we wish to avoid talking in circles. At some level, this means we must have a respect for the basis of tradition Western Thought, Aristotle's Three Laws of Thought (Law of Identity, Law of Non-Contradiction, and Law of the Excluded Middle). Why do we need help from traditional Western Thought? It is not an arbitrary bias. When we ignore Aristotle's Laws of Thought (especially Non-Contradiction) the conversation quickly becomes surreal. Common terms - truth, value, reality, consciousness - can imply entirely different and contradictory things to the parties of the discussion.

As Socrates said, "The beginning of wisdom is the definition of terms". If we allow an important term simultaneously refer to multiple contradictory or vague concepts during a discussion, all hope of common understanding vanishes. This is the basis for any discussion I intend to have, and won't waste my time or energy (or sanity) by pointlessly arguing about idealistic fantasies based on shifting and vague definitions. G. E. Moore strongly believed that muddled thinking and imprecise language confuses our thinking about reality. He thought that a combination of common sense and precise language were sufficient to address most philosophical questions. Because of the laxness in our use of language when addressing complex issues, philosophers exacerbate already complex issues and frequently create problems out of nothing.

I have been frustrated in my conversations with the kind of people who toy with words and meanings simply for the pleasure of being clever and evasive. They equivocate on the important concepts like truth, meaning, free will, faith, belief, trust, experience, existence, good, bad, etc. They redefine these, sometimes in mid-discussion, using them in varying ways that suit their desired outcome. This convenient juggling of meanings is very much in the spirit of the disreputable philosophical style called "Deconstructionism". In particular they frequently equate "faith" in science (belief or "trust" based on methodology and evidence) with "faith" in religion (belief in the complete absence of evidence). It is unfortunate that the word, "faith" spans both of these domains. Its use with respect to the evidence of our senses only confuses the discussion. "Truth" is another word that is used in entirely different ways by different people. To a person taking a rational approach, truth is the outcome of a logical process (a proposition is either true or false, but not both). To a person approaching philosophical questions from a religious or mystical point of view, truth can mean whatever concepts they feel are enlightening, thrilling, uplifting, motivating, or emotionally satisfying. The multiple, inconsistent use of words like these are cases of allowing ourselves to be confused by the imprecise use of language. The entire epistimologies feeding these different world views (science/evidence vs mystical/religious) differ. The religious belief is based on revelation / inspiration / emotion, and the scientific world view is based on observation / experiment / measurement / evidence / methodology / replication. As Wittgenstein said, "Philosophy is a battle against the bewitchment of our intelligence by means of our language". These questions are hard enough without allowing additional confusion to creep in through the lazy and imprecise use of language.

There is one clear prerequisite for people to be able to understand, evaluate, and debate the reasons that others offer for their viewpoints, and that is that they have to understand each other. The only way to understand each other and to engage in meaningful discussion is to use a common, neutral, language, not one that is front loaded with irrational assumptions. As soon as you inject religious or mystical beliefs or doctrine into a discussion or debate, it essentially shuts down the discussion with anyone who doesn't share that mystical belief system. Falling back to religion, mysticism, miracles, serves as a conversation stopper. Once someone invokes a religious or supernatural doctrine as a basis for their position, they are effectively shutting out anyone who doesn't share those precepts and that is the end of the discussion.

All discussions of vocabulary aside, we are all "realists" when dealing with the physical world and living our lives. It is only when sitting around the coffee table debating late into the night that the "idealist" comes out of hibernation. Idealism (roughly, the theory that reality is created by the mind, or that the objects of perception consist solely of ideas) is an intellectual indulgence and luxury. When someone says "how do you know that reality exists?" they are usually being coy. I say this because anyone can observe that with every action we take, we all demonstrate a complete trust in the physical reality of the external world. Every action is an accommodation and/or reaction to real world events. None of the several billion people on the planet conduct themselves as if the bus racing towards them on the highway is an illusion or someone else's biased view of reality that they may not necessarily subscribe to. To propose that they don't truly know if the bus is really barreling down on them shows a huge mismatch between their actions (i.e. running for safety) and their words, and in my opinion shows them to be, at best, disingenuous or confused, and at worst, liars.

Existence of an external reality

How often do you run across someone who insists that "so-called reality" is an illusion, that we can't prove that it exists, that everything might be a dream or hologram or hallucination, or that "your reality is not my reality"? Actually, in Boulder, CO, quite a lot. The reason this keeps coming up (as it has for centuries) is that it is difficult, if not impossible to prove beyond a shadow of a doubt that the reality that seems to be around us actually exists independently of us. In the next few sections, I will outline the many ways that have been presented over the years to give us confidence that it really is there.

It’s hard to imagine how anyone could question reality’s existence, which is close to questioning existence itself. But they are out there: solipsists who doubt all existence, and even doubt that minds other than their own exist, Idealists, some mystical eastern religions like Advaita, and adherents to fringe pseudo-religions like the Unitarian Church's “Course In Miracles” who at least agree that we all have minds, but that the physical world might be an illusion. One could wisecrack that this tendency to deny reality might have been bred out of the human race over time if there were a genetic component to such beliefs – that they would have stepped off the curb in front of a car (or chariot, or saber toothed tiger). But I imagine that even these people look both ways before crossing the street. When it comes to actually living in the world, we all interact with it as if we were realists, regardless of what other philosophies we may profess.

Fair warning - I approach this discussion from the point of view of a Philosophical Realist, also called Metaphysical Realism. I believe that "truth" is measured by the mind's correspondence to reality. I accept that the world is pretty much like our senses, and our science shows it. To give it another name, I am also a Philosophical Naturalist - I think that the observable universe is all there is, and is all that we need to concern ourselves with. There is an external reality that exists independent of our senses, and is there when we are not present to observe it. Other metaphysics (Idealism, Subjectivism, Relativism, Solipsism, Dualism, Monism, etc) so blatantly contradict common experience or are so obscure that I can't accept them. The only philosophical choice which the evidence of our experience supports with every action we take is Realism. When we look both ways when we cross the street it is because at our core, we are all realists.