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?
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.
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.
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?
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.
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.
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?
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