Here is a brief digression from my Ultimate Challenge series. I guess reading philosophical agruments makes me imagine that I am a philosopher. If any of you are actually trained in philosophy, please let me know how the following argument is wrong.
People often say that science is dogmatically committed to the idea that everything that exists is physical.
This claim bugs me. It feels wrong.
Not wrong like a straw man – there are many atheists, naturalists, and scientists who probably fit the claim. But I’ve always had this sense that naturalism sort of “falls out” from what science is.* It’s not this whole extra assertion tacked on alongside things like “remove bias where possible” and “keep hypotheses simple”.
I’ll admit it – my discomfort with the claim is personal. I am a scientist, and I am a naturalist. When someone says that scientists or naturalists are committed to the a priori claim that supernatural causes do not exist, I feel like I’ve been accused of something slightly dirty. Something that I am innocent of.
This post is an attempt to examine the claim. I want to clarify the concepts for myself, in case I am not, in fact, innocent of what they accuse me of. I also want to share my understanding with you, my readers, so you can point out any errors in my thinking.
So let’s start with this question:
Can anything non-physical exist?
Like good philosophers, we’ll begin by exploring what “physical” and “exist” mean from a scientific viewpoint. I hope that my definitions – and the reasoning that flows from them – will be acceptable more generally among naturalists, but the only thing I promise you is that these are the definitions that I currently work under.
Okay, let’s start with “physical”. What does it mean to be physical? What sorts of things are physical? I’m going to use a definition that fits neatly with how science examines things. Here goes:
Anything that has observable effects is physical.
Science examines the physical universe. And, broadly conceived, science can be used to probe anything for which we can generate observations, from atomic interactions, to planetary orbits, to human behaviour, to … whatever. If you can record an observation about it, it is accessible to the methods of science. And thus, it is part of the physical universe (as science conceives it).
Now, the above definition of physical is still a little too vague. What does it mean to observe something? Scientists use a multitude of tools for observation, from their own senses, to obvious “scientific” instruments such as microscopes, telescopes, barometers, rulers, and stopwatches, to less obvious instruments like surveys, explosives, and blocks of glass. When I say “observable”, I mean anything that could, in principle, affect the measurements we make using these or any other conceivable measuring instrument. In other words,
All and only things that can interact causally with the world we experience are physical.**
Wait a minute. This seems a wee bit dodgy. Under this definition, a whole lot of stuff most of us call non-physical seems to suddenly be classed as physical. After all, ghosts, gods, and souls are often claimed to be non-physical, but if any of the claims about them are true they certainly affect the world in ways we can notice. Do we really want to call these immaterial things physical?
Maybe not, but consider the alternative. Remember that anything that can interact causally with the world we experience is within the realm of scientific investigation, at least in principle.
So either these things – ghosts, gods, souls, etc – are defined as non-physical, in which case science is able to investigate the non-physical (because it can investigate them, through their effects on the physical world), or these things are physical (for this particular pragmatic definition of “physical”), and science remains limited to investigating the physical. I recognize that these things are special to many people, but I have yet to see a good definition that divides physical things which have effects in the world from non-physical things which have effects in the world.
So I’ll stick with a definition of physical that aligns with scientific methods.
Second, what do we mean by exist? I’m going to keep this simple and pragmatic.
All and only things that can interact causally with the world we experience exist.
Because if it can interact with the world of our experience, then clearly it exists. And if it can’t affect or be affected by this world, then its “existence” is irrelevant, and basically meaningless, as far as I’m concerned.
So now we have our definitions. What do they tell us about the question?
Can anything non-physical exist?
I’m sure you already see where this is leading, but let’s make it even more clear by substituting our definitions for the words themselves:
Can anything [that cannot interact causally with the world we experience] [interact causally with the world we experience]?
Of course not. Problem solved. Well, not just yet.
Let me anticipate two of the objections that I’m sure have leaped to your minds, then I’ll open the floor for discussion.
1. There’s no philosophy here, just careful selection of definitions.
Absolutely correct. (Though much of the groundwork of philosophy – as with science – is in pinning down definitions.) But note that I didn’t pull my definitions out of thin air, or generate them specifically so I could support my conclusion. The definition of “physical” is grounded in the way science is done. It may not be your definition. It may not fit with anyone’s intuitive idea of “physical”. But it is a definition that is on the table when we’re discussing science and scientific materialism. And the definition of exists … well, this has a more informal motivation, perhaps, but I don’t think it’s entirely arbitrary. If anyone objects to it, please let me know of some reason we should care about the existence of something that can’t, even in principle, interact with the world of our experience (or accept the non-existence of something that does interact with the world).
2. This doesn’t say anything about the existence or non-existence of gods, souls, etc.
Quite right. By redefining these things as physical, I have not altered their properties, or the fact of their existence or non-existence.
But remember – this essay was not meant to argue for atheism, or to suggest that entities traditionally conceived of as non-physical do not exist. My line of thought was exclusively aimed at helping decide whether naturalism – the claim that only physical entities exist – is an extra assumption of science (a dogma, if you will), or whether it is an automatic consequence of more basic aspects of science.
I think I have shown that it is not an extra, separate dogma. In fact, I think I have shown that metaphysical naturalism (not just methodological naturalism)* is an automatic consequence of defining “physical” in a scientific sense, and defining “exists” pragmatically.
Now, since I am not a trained philosopher, I need some feedback. What have I overlooked? What have I screwed up here? Or, if I’ve got this right, who else has come up with this reasoning before me? I know I’m not the only one to think of it.
* Note that, when doing science, we use methodological naturalism – that is, we’re free to believe that other stuff exists, but what we’re studying in science is just the natural (physical) stuff. People who identify as naturalists (such as me) go further, to metaphysical naturalism – the claim that there actually probably is no other stuff besides what’s physical.
** Yes, I know there is still vagueness in these definitions. If you think the remaining vagueness is terminal to my argument, let me know. Otherwise, I plead the requirements of brevity as an excuse to be less precise and wordy than a proper philosopher would be.