What Is Realism?

Do you believe in the existence of stones, trees, cats, and the other everyday objects around us? It’s not a rhetorical question — there are actually philosophers who don’t believe in the existence of this sort of thing. What about the objects of mathematics? — numbers, abstract triangles, infinite quantities? How about the entities and laws of science? Or moral and aesthetic properties? What sorts of furniture are you willing to stow in the universe’s metaphysical attic?

Realism and Language
There is a school of thought that categorizes realism as a doctrine about truth and language instead of existence — the idea being that talking about the existence of sorts of things, and what it means for our talking to correspond to some sort of truth, is the real job of this branch of philosophy. This school of thought will be blatantly ignored by me in this piece, though those who are interested in finding out more can get lots of great references from Michael Devitt’s Realism and Truth.

Realism in philosophy is, broadly, a belief in the existence of some sorts of things. If you believe in the existence of numbers, you are a mathematical realist. If you believe in the existence of unobservable subatomic particles, you are a scientific realist. And so on, through the rest of the disciplines into which philosophy delves — ethics, aesthetics, language, and logic, to name a few.

Of course, just as there are realists about each of these sorts of things, there are also anti-realists — self-proclaimed disbelievers in the existence of those types of objects — and many a heated battle has been waged between the two camps in just about every arena.

Common-Sense Realism

What I’d like to talk about initially is realism (and anti-realism) about a sort of object that many of us take for granted as having an uncontroversial existence: stones, trees, and cats; the everyday objects of the external world. Let’s call this doctrine common-sense realism.

I said “external world” in the previous paragraph as a hat-tip to the debate that pretty much gave birth to the very notion of realism in the modern era: Cartesian skepticism. Rene Descartes, in his Meditations, pondered the objects about the existence of which he could be absolutely certain. In the end, he cast considerable and powerful doubt on the existence of even such mundane and seemingly certain things as stones, trees, and cats, saving his indubitable belief solely for the existence of his own mind. Descartes’ skepticism was so powerful, in fact, that it spawned an incredible genealogy of philosophers arguing about it for centuries to come. In the end, Descartes himself, with the generous and dubious help of his God, wound up believing in stones, trees, and cats, but other philosophers would not so easily shake off the doubts Descartes had raised. George Berkeley, for one, posited that, post-Descartes, it only made sense to believe in the existence of minds — not in the existence of stones, trees, and cats at all. (Stones, trees, and cats, on Berkeley’s take, are actually collections of ideas, which are, as ideas, completely dependent on minds for their existence.) So, thanks in part to Descartes, we have a divide that persists in our thinking about these things to this very day: there is the internal world (our minds) and the external world (stones, trees, and cats). Thanks to the certainty Descartes uncovered, almost no one until recently has been an anti-realist about minds; but many have been anti-realists about the external world.

So there are two facets to being a common-sense realist. It means, for one thing, that you believe in the existence of things like stones, trees, and cats; but for another thing, it means that you don’t think such things are dependent on minds for their existence. A tree, for a common-sense realist, is a real object in the real world, and would exist whether or not humans ever thought about it.

Mind Dependence
What sorts of things would be dependent for their existence on minds? Unless you are a disciple of Berkeley, this might be an odd question. But ponder things like dreams, emotions, and ideas. Clearly these sorts of things are mind-dependent. A stone, on the contrary, if you’re a common-sense realist, exists whether or not any minds exist. The fact that, e.g., dreams are mind-dependent puts them in an odd metaphysical category based on our criteria here. But we can put this to one side for the time being, noting that the fact that mind-dependent entities are mind-dependent is more of a boring truism than an earth-shaking metaphysical revelation.

So if you believe that stones, trees, and cats exist even when you’re not thinking about them, you are a common-sense realist. You might, naturally, be wondering why anyone would be an anti-realist about this sort of thing, or bout anything, for that matter. Well, actually, not a lot of philosophers since Berkeley are common-sense anti-realists. But anti-realism becomes a lot more attractive in other realms.

What other sorts of realism or anti-realism might you buy into?

Scientific Realism

If you’re a common-sense realist, you are also likely to be a scientific realist. Scientific realism is the doctrine that not only do stones, trees, and cats exist, but so do the objects that science posits. If you’re a scientific realist, you include amongst the furniture of your universe such so-called “unobservable” subatomic particles as electron, bosons, and quarks, as well as objects and phenomena on the other end of the magnitude spectrum such as black holes, gravity, and an expanding universe. One problem with scientific realism is that scientific theories are sometimes wrong, and so the objects that these theories posit can be fictional in the end. One favorite example in the literature is a 17th century theory of combustion that posited the existence of a substance called phlogiston. The theory, while scientifically accepted at the time, turned out to be wrong, and phlogiston was shown not to exist. So a 17th century scientific realist would have been put in the awkward position of believing in the reality of something that didn’t in fact exist.

How does a scientific realist come to grips with such uncertainty? Well, the general response from scientific realists is that this is the best we can do. Sure, science is sometimes wrong, but it’s still our best bet for uncovering the true nature of the universe. There is no non-scientific, privileged position from which we will ever be able to see the entire truth about the world — there is no window into the room that holds all of the furniture of the universe. Our current scientific theories provide the best view we can get.

Mathematical Realism

If you are a scientific realist, you might also be a mathematical realist, seeing how science and math seem to be so tightly bound together.

Actually, though I am a common-sense and scientific realist, my favorite brand of anti-realism is mathematical anti-realism. I have a hard time stomaching the idea of numbers and similar abstract objects existing independently of minds. I’m not alone in my distaste of mathematical realism, but those of us so disposed do face many issues — chief among them the seeming indispensability of math to science. If one is a scientific realist, and science relies indispensably on math, then on the face of it it seems as if one is committed to the existence of mathematical entities, whether or not one likes it. This indispensability argument has kept philosophers of math very busy over the last few decades.

For many of us on the anti-realist side of the mathematics debate, the big problem is that of causal inertness. Mathematical objects are, by consensus at any rate, abstract — that is, they take up no space and have no causal powers whatsoever. You can’t throw the number 8 through a window, for instance. And yet for a mathematical realist the number 8 still exists, somehow, and is indispensable to science. This sort of existence, for many of us, is just a completely different sort of thing from trees and quarks, which are just the sorts of things that can be thrown through windows. (Though you have to be pretty skilled to throw a quark anywhere.) For a mathematical anti-realist, it makes more sense to think of the number eight as a useful fiction; like Holden Caulfield with an advanced degree in particle physics.

Moral Realism

I’m probably the worst person to be writing about moral realism, because I never really understood what it was supposed to accomplish to posit actual entities/properties (philosophers talk more about moral properties than entities) of ethics. And yet, on certain takes, this is exactly what moral realism posits. At least mathematical entities are tightly bound to the entities of physics. Moral properties, if they were to exist, would be tightly bound to human psychology and systems of justice — both clearly dependent on human minds for their existence.

Mostly, the case for moral realism is stated in terms of semantics instead of existence — moral realists say that moral statements can be taken to be objectively true or false, in opposition to some common-sense intuitions that moral statements are subjective and/or dependent for their validity on the cultures in which they are uttered. But if “that cat is black” is a true statement because there is indeed a black cat in front of you, then “that person is virtuous” could be held to be true in the same way: there is indeed a virtuous person in front of you. This would, on a naively reasonable take, put virtuousness on a par with blackness; but while one is easily cashed out in terms of low-grade, mind-independent physics, the other is all bundled up with arguably less objective mind-dependent concepts. That’s why I am a moral anti-realist.

What Kind of Realist Are You?

Chat us up in the comments!

Are We Living In A Computer Simulation?

We recently explored Cartesian skepticism, and its dark conclusion that we can’t know for sure that the external world exists. This post is in a similar vein, as it asks the question: Are we unknowingly living in a computer simulation? One difference between this dark idea and Descartes’ is that if we are indeed living in a computer simulation, there definitely would exist an external world of some sort — just not the one we think there is. Our simulators, after all, would have to live in some sort of an external world, in order for there to be computers upon which they could simulate us. But, of course, the world, on this scenario, that we think of as existing would be a mere virtual creation, and so, for us (poor unknowingly simulated beings) the depressing Cartesian conclusion would remain: our external world does not truly exist.

Of course, if you’ve been even a marginal part of contemporary culture over the last decade or two, you know the movie “The Matrix”, the premise of which is that most of humanity is living mentally in a computer simulation. (Physically, most of humanity is living in small, life-sustaining pods, in a post-apocalyptic real world of which they have no awareness.) You no doubt see the parallel between “The Matrix” and the topic of this post. (Other movies with similar premises include “Total Recall” and “Dark City”, and surely many more that I can’t think of off the top of my head. Which makes me think we have to do a philosophy-in-the-movies blog post soon…) But rest assured that this is no banal foray into Keanu Reevesean metaphysics. (“Whoa.”) The subject of existing in a computer simulation has been pored over to a dizzying extent by philosophers. There’s a lot of meat on this philosophical bone.

Nick Bostrom’s Simulation Argument

Nick Bostrom, a philosopher at Oxford, has developed a most interesting argument, the gist of which is to strongly suggest (with a high degree of probability) that we may indeed all be living in a computer simulation. His clever argument discusses advanced civilizations whose computational technology is so powerful that they can easily and cheaply run realistic simulations of their ancestors — people like you and me.

If these advanced civilizations are possible, then, says Bostrom, one of these three hypotheses must be true:

(1) Most (as in an overwhelmingly high statistical majority) civilizations that get to this advanced computational stage wind up going extinct. (The Doom Hypothesis)

(2) Most (as in an overwhelmingly high statistical majority) civilizations that get to this advanced computational stage see no compelling reason to run such ancestor simulations. (The Boredom Hypothesis)

(3) We are almost certainly living in a computer simulation. (The Simulation Hypothesis)

Bostrom claims that (1) and (2) are equally as likely as (3), but, really, it’s fairly straightforward to assume that they are both actually false. The Boredom Hypothesis, in particular, seems rather implausible. Though we don’t know what such an advanced civilization would think of as worth its time, it’s not unlikely that some significant fraction (at least) of advanced societies would run such easy and cheap simulations, either out of anthropological curiosity, or even for just entertainment purposes. (A lot of our best scientists surely play video games, right?) The Doom Hypothesis is slightly more plausible. Perhaps there’s a technological boundary that most civilizations cross that is inherently dangerous and destructive, and only a negligible fraction of civilizations make it over that hurdle. But it’s still tempting and not unreasonable to think that such a barrier isn’t inherent to social and scientific progress.

So, if civilizations don’t generally extinguish themselves before reaching computational nirvana, and if they don’t think that the idea of running ancestor simulations is a silly waste of time, then we have a clear path to the Simulation Hypothesis. Say that a thousand civilizations reach this computational stage and start running ancestor simulations. And say these simulations are so easy and inexpensive that each civilization runs a trillion simulations. That’s a quadrillion simulations overall. Now divide a quadrillion by however many civilizations there are in the universe, which is perhaps far less than a quadrillion, and you get the odds that you are living in a simulated civilization. Say, for the sake of argument, that there are a million civilizations in the universe. The odds are then a billion to one that you are living in a real civilization. The far more likely proposition is that you are living in a computer civilization.


One key assumption upon which this argument relies is that things like minds and the civilizations in which they reside are in fact simulatable. This is a contentious claim.

The theory that minds are able to be simulated is often labeled “functionalism” — it gets its traction from the idea that perhaps minds can emerge from hardware besides human brains. If we meet an alien from an advanced civilization, learn her language, and converse with her about the meaning of life, we’d like to say that she has a mind. But, if upon scanning her body, we discover that her brain is in fact made up of hydraulic parts, rather than our electro-chemical ones, would her different hardware mean that she isn’t possessed of a mind? Or would it be the case that, in fact, minds are the kinds of software that can run on different sorts of hardware?

If this is indeed the case, than minds can be classified as functional things — that is, a mental state (say, of pondering one’s own significance in an infinite cosmos) is not identical with any particular brain state, but is some sort of functional state that can be realized on all different sorts of hardware. And if this is true, then there’s no reason, in principle, that a computer couldn’t be one of those sorts of hardware.

Given our “successes” in the field of Artificial Intelligence (AI), I have long been skeptical of our ability to create minds in computers. And there’s a proud tradition in philosophy of this sort of skepticism — John Searle, for instance, is one of the more famous anti-AI philosophers out there. (You may have heard of his Chinese Room argument.) But, by and large, I think it is fair to say that most philosophers do come down on the side of functionalism as a philosophy of mind, and so Bostrom feels comfortable using it as a building block to his argument.

I can’t, in this post, get into the debate over AI, functionalism, and the mind, but I will pick on one interesting aspect of the whole simulation issue. Every time I think about successful computer simulations, my mind goes to the simulation of physics rather than the simulation of mental phenomena. Right now, I have a cat in my lap and my legs are propped up on my desk. The weight and warmth of my cat have very diverse effects on my body, and the extra weight is pushing uncomfortably on my knees. My right calf is resting with too much weight on the hard wood of my desk, creating an uncomfortable sensation of pressure that is approaching painful. My right wrist rests on the edge of my desk as I type, and I can feel the worn urethane beneath me, giving way, in spots, to bare pine. My cat’s fur fans out as his abdomen rises with his breathing — I can see thousands of hairs going this way and that, and I stretch out my left hand and feel each of them against my creviced palm. The fan of my computer is surprisingly loud tonight, and varies in pitch with no discernable rhythm. I flake off one more bit of urethane from my desk, and it lodges briefly in my thumb’s nail, creating a slight pressure between my nail and my flesh. I pull it out and hold it between my thumb and finger, feeling its random contours against my fingerprints.

At some point, you have to wonder if computing this sort of simulation would be just as expensive as recreating the scenario atom-for-atom. And maybe if a simulation is as expensive as a recreation, in fact the only reliable way to “simulate” an event would actually be to recreate it. In which case the idea of functionalism falls by the wayside — the medium now matters once again; i.e., feeling a wood chip in my fingernail is not something that can be instantiated in software, but something that relies on a particular sort of arrangement of atoms — wood against flesh.

Who knows, really? Perhaps future computer scientists will figure out all of these issues, and will indeed usher in an era of true AI. But until it becomes clearer that this is a reasonable goal, I’ll stick with my belief that I am not being simulated.

If I am being simulated, a quick aside to my simulator: Perhaps you don’t like meddling in the affairs of your minions, but I could really use a winning lottery ticket one of these days. Just sayin’…