Hi, you are listening to the HPS podcast, where we discuss all things history, philosophy, and social studies of science for a general audience. Today I am your host, Samara Greenwood.
In this episode I talk with Caleb Hazelwood, a philosopher of science and PhD candidate, on the topic of Scientific Metaphysics.
The term ‘metaphysics’ – especially when used in relation to science – can conjure up various meanings for different people. However, as Caleb explains, in this context – ‘metaphysics’ refers to coming to grips with what ‘really is’ in the world – and being crystal clear about the concepts we use to describe natural phenomena and how they interact.
For example, Caleb talks about the importance of differentiating between entities we consider largely stable and timeless across the universe – such as the elements as collated on the periodic table – compared with more time-bound and space-bound entities – such as biological species.
Another important question tackled by metaphysicians is: how can we best define causation? Here, Caleb argues for what is called an ‘interventionist’ or ‘manipulability’ theory, which looks at how scientists typically link changes in entity X to changes in entity Y – and calls for that scientific practice to act as the best baseline for philosophical understandings of cause and effect.
While exploring such fundamental questions may appear to some as difficult and abstract, Caleb shows how debates such as these provide for fruitful interactions between scientific practice and philosophical reasoning.
Samara Greenwood: Caleb, welcome to the podcast. Lovely to have you here.
Caleb Hazelwood: Thank you very much. I'm really glad to be here.
Samara Greenwood: I do ask my guests to start off to give us a little intro into your background. How did you come to history and philosophy of science?
Caleb Hazelwood: This is a story I love to tell because I love to give my undergraduate advisor a shout out any chance I get.
So, I was at a very small state school during my undergraduate in Missouri. I was on the pre-med track; I was studying to go to medical school, and I needed to fill an elective. And so, I saw this class philosophy of biology taught by Catherine Kendig, who's now at Michigan State University, and I took the class thinking, okay, I'll get a humanities credit, I'll fill the elective.
But as is the case with so many, curious folks who go into these classes sort of naively, my mind was just blown at how you could ask questions about biology in this way with these kinds of tools. And so I just started taking all of the HPS courses I could. And that's all she wrote.
Then it was a master's and now a PhD.
Samara Greenwood: And what's your PhD topic? [01:00]
Caleb Hazelwood: My PhD topic is causal modelling in evolutionary biology. I'm really interested in the kinds of beliefs and assumptions that practitioners make about causation in evolution and what their models tell them about that.
I'm also really interested in relationships between populations and individuals and some issues that might arise when we get those two confused.
Samara Greenwood: Mm, that's fabulous. I'm interested in what is a topic in HPS that you believe would be of interest to a broader audience?
Caleb Hazelwood: I've been thinking a lot recently about the topic of scientific metaphysics. It intersects with my work all the time. I just can't seem to avoid it. Recently I've just decided, look, I'm going to tackle this head on. And I think part of my project is evangelizing a little bit and encouraging others to think about metaphysics as well.
Often in our corner of history and philosophy of science the word metaphysics can be a bit of a naughty word. I see it as part of my job to help rehabilitate that word for us.
Samara Greenwood: All right, so can you then give us a little rundown on what you mean by metaphysics in this sense? [02:00]
Caleb Hazelwood: Yes, absolutely. And it's a very loaded term, of course, that has meant a lot of different things to a lot of different people. But when I talk about metaphysics, I'm really talking about what it means to give an account of the way the world really is. Immediately a lot of interesting questions crop up out of that because we are these flesh bound, embodied creatures who are navigating around the world, but we still are curious about that world, and we want to be able to say true things about it.
Some people look for what they call the objective, mind independent reality, right? The thing untouched by, unadulterated by human perception. It's this idea that there is this world out there that exists independently of human investigation and understanding.
And then some folks reject that entirely, right? And they just say, look, there is no way to conceive of or talk about some kind of mind independent reality. For them, metaphysics means something like empiricism, right? What is practice? What does scientific practice tell us about the way the world really is? And is that the best that we can do in putting together an account of what's out there, quote, unquote?
Samara Greenwood: So, can I ask what your take on metaphysics is?
Caleb Hazelwood: Yes, of course. Now, this changes all the time, I'll set this in stone now, but don't hold me to it if I print something that goes against it. I like to think that I'm a metaphysical realist. I think we can say things about the world, and they can be about the way the world really is.
But also, I'm very much sensitive to scientific practice, right? I'm very dubious about the idea that there is some mind independent reality that we can get in touch with. I think that our empirical efforts are our best ways of doing metaphysics. I often think that the line between empiricism and metaphysics or epistemology and metaphysics is, in many cases, an artificial line. That's where I stand today.
Samara Greenwood: And so, in practice when you're exploring metaphysics, what kind of things do people look at? [04:00]
Caleb Hazelwood: A lot of metaphysics deals with carving up the world. Carving nature at its joints. So, metaphysics often involves classifying, or building taxonomies of what's in the world.
Some people do this in terms of things they call natural kinds. So, trying to find these groups in the world that exist for some reason, some kind of mechanism or something that holds them together. A lot of times people will say the elements, the table of the elements, is a table of natural kinds. Because all hydrogen atoms are unified by the fact that they have one proton, for instance.
Things get a little trickier when you leave the physical and chemical sciences, and you start to think about biology. Some people want to look for classifications such as species, right? This is a metaphysical project trying to carve the organic world into species. But of course, as anyone with even the least bit of biological training knows there are so many ways to carve up the world into different species, many of them incompatible, many of them butting up against each other. And so this is a kind of metaphysical question that philosophers of biology have spent decades thinking about.
Samara Greenwood: Okay. And are they coming to any conclusions? [05:00]
Caleb Hazelwood: Recently anyway, I think the relative consensus is that species are individuals, spatio-temporally restricted individuals.
They're not classes of things in the way that hydrogen is a class, and it can have members of that class all over the universe. Species don't really work that way, right. Species have to exist in the same time and place. While species taxa can be real, right? So, Homo sapiens is a real thing and Physeter macrocephalus [Sperm Whale] is a real thing, there's no species category that kind of binds all of these things together, right? That might actually be something more heuristic - of more practical value - and it is of practical value. Can you imagine telling biologists that tomorrow they need to eradicate the language of species from their writing and their research? No. So it hangs around for good reason, but it's unclear that the term actually unifies all these concepts in some way. We're dubious about that.
Samara Greenwood: Are there some other examples? Are there particular interests you have in metaphysics of science that you think are particularly interesting to others as well?
Caleb Hazelwood: Certainly. So recently I've been thinking about individuality, so this is a very fun one.
If you think about what it means to be a biological individual, you suddenly come across an embarrassment of possible candidates for those explanations, right?
I look at myself and I think, okay, well I'm probably a good individual, right? That makes sense, I can individuate myself. I'm different from my environment, I'm different from Samara, so I must be an individual. But then I think, well, wait a minute, there are 13 trillion microbial cells in and on my body of many, many different species, many different phyla…different domains, for God's sake. And we all seem to be functioning as a whole, as a cohesive unit.
So, what does that mean? Is Caleb the individual? Does he stop at the Homo sapiens DNA, or do I stop at the various microbes on my fingertips? How can we cash that question out?
Well, there have been numerous attempts to provide an explanation of what it means to be a biological individual. People like Thomas Pradeu have offered an immunological account, right? So they say, well, look, the individual is what the immune system lets in, and everything the immune system pushes out is other. That's not part of the self. That's one answer. But then of course people who deal with thyroid disease are going to immediately have counter examples to something like that.
Then also people want to talk about individuality in terms of evolution. They want to say, maybe the individual - from the biological perspective - is what natural selection acts on. Maybe that is what the individual is. Then of course, we get into a whole new suite of problems because we've got to think about what natural selection can act on. What does it take for something to be visible to natural selection?
So that's another example where thinking about something as fundamental as an individual from a biological perspective can get really messy.
Samara Greenwood: When you were talking about individuals and where's the boundary, is there some discussion about fuzzy boundaries versus hard boundaries? Does that come into the discussion at all?
Caleb Hazelwood: Yes, definitely. But there's something almost like a pill that we've got to swallow, right? Because there's something that butts up against our intuition when I think maybe there's a fuzzy boundary between me and the world, right?
We navigate the world thinking there is a hard and fast boundary between me and my environment. It's psychologically weird to think of me blending in with the chair that I'm sitting on and even blending in with, the environment around me.
But yes, there is certainly the school of thought that organisms, individuals are abstractions. They are just abstractions from the otherwise pretty messy, fuzzy, blurry world.
Samara Greenwood: I know you also had an interest in population level versus individual level explanations in natural selection. [09:00]
I suspect that's of interest to a broader audience. Could you tell us a bit more about that?
Caleb Hazelwood: For the past couple of decades there's been a debate in the philosophy of biology about the nature of selection. Whether natural selection is really a cause in the world, or if natural selection is just this epiphenomenon that appears as a result of living and dying and mating and eating and praying, that happens at the individual level.
So, if it is a cause, is it a cause that happens at the population level? Or is it a cause that happens to individuals, or is it really just a statistical aggregate, just a theoretical construct?
Now this debate in maybe the last 10 years or so has been set aside because it got to a bit of a stalemate. At the end of the day, it was - well look, you call something causal, I say something is non causal. It's not clear what kinds of arguments we could marshal to convince each other otherwise. We can bring in as many examples from practice as we want but that's not going to seem to do it either. If you and I have different intuitions about what it means for something to be a cause then it's not clear what the examples from practice are going to do to help resolve that debate.
That was the case until recently when Charles Pence published in the Cambridge Elements of Philosophy of Biology on the causal structure of natural selection, where he has revived this causalism-statisticalism debate as it's called, but also put it in contact with other literatures. Literatures such as the extended evolutionary synthesis, which is a relatively new idea. It's a criticism of the standard modern synthesis, which depicts evolution as a gene- centric phenomenon with natural selection happening to organisms that are passively accepting these environmental pressures. [11:00]
By putting these literatures in contact and thinking about the difference between population level explanations and individual explanations, and how different biologists are going to appeal to different levels of explanation for their own empirical interests, this helps us really put some of these questions in context and get a better grasp on them.
Samara Greenwood: That makes sense. So rather than sticking with polarized debate, if we bring in more literature and more perspectives, we can start to tease apart some of the finer details. Would that be true?
Caleb Hazelwood: Absolutely. Do you find this to be true? I feel like so often in philosophy or history and philosophy of science, we'll get pigeonholed in our problem just by reading the literature or the debate between the figures that we're interested in.
But if you just zoom out a little bit, you find that somebody else was talking about something kind of analogous but made a conceptual or argumentative move where you’re like ‘Holy Cow, that's what I needed.’
Samara Greenwood: [12:00] I think it really helps too when you can jump out of standard thinking being done in that space to bring something fresh in. It really does enliven the debate.
You've got some current work with Yasmin Haddad on the metaphysical aptness of interventionism in biology. Okay, you're going to have to explain that one to me.
Caleb Hazelwood: Yasmin Haddad is a postdoc with Ford Doolittle's Group in Halifax, Canada. She and I met about a year ago and have just been having discussions where we realized we both really like thinking about causation and biology. And we both have this very radically practiced informed view of metaphysics.
We want to be metaphysicians. We want to say we are making claims about the way the world really is, but we also want to do it in a way that's super consonant with what biologists are doing. We think it would be kind of silly to do otherwise, right? So, we're working on a project called ‘The Unbearable Lightness of Intervening.’
Samara Greenwood: I love that title.
Caleb Hazelwood: Thank you. So, we are trying to develop a realist metaphysics for manipulability theories of causation. [13:00]
Philosophers love talking about causation in case the listeners have not yet gathered that. We just love it. And there's a huge debate, there's a huge literature, on what it is for something to be a cause.
So, some people say that a cause is something that transfers some amount of energy or transmits a mark. Some people say causes are things that raise the probability of an event. Some people say that causes are mechanisms. They are entities organized in a certain way that have activities and produce something at the end. There's just a litany of different attempts to pin down what it is we mean when we talk about a cause and a scientific explanation.
Out of, I think, frustration with this metaphysical speculation, you've got some folks like Judea Pearl and especially James Woodward who have offered manipulability theories of causation where basically, to paraphrase, they say, look, if you wiggle Variable X and under the right conditions, you always see a wiggle in Variable Y then you can talk about X being a cause of Y.
This interventionist approach gives us a way of picking out causal relationships. It doesn't necessarily let us look under the hood, and tell us what makes it a causal relationship or what's really happening at the fundamental physical level or something like that. But, it helps us pick out causal relationships in the world.
Now metaphysicians have often been a bit critical of this view because they call it metaphysically light, right? They say, it's not metaphysically robust because it's not giving us an account of what causation really is, what is the true nature of causation?
So, interventionism takes some slack for that reason. Woodward has been aware of this and has responded to this criticism in several places. One of them, my favourite, is a 2017 chapter where he has this polemical dialogue with a made up character called Professor Metaphysico where he and professor Metaphysico debate about the sort of metaphysical sturdiness of his concept of causation. [15:00]
Yasmin and I see this as a way to take our very practice-centred metaphysics, but also our desire to be good realists, and put them together. We say, if science is our best way of doing metaphysics, if science is our best way of coming up with an account of what's out there in the world, and science relies heavily on this notion of causation as intervention, then maybe that's actually as metaphysically sturdy account as you're going to get, and maybe that should be the benchmark. Maybe when we talk about the metaphysical ‘oomph’ of an account of causation, maybe that ought to be the benchmark, since interventionism is so central to scientific practice. That's where we ought to get our metaphysics from.
Samara Greenwood: That's really interesting.
So we've learnt a little bit more about metaphysics of science. How do you see that being of value to your practicing scientist, but also perhaps just to a more general audience? What should be of interest to them here? [16:00]
Caleb Hazelwood: I think that the easy way out is to say something like, well, surely you want to talk about what's real, right? Surely you want to believe the things that you're studying are real? So, it's important to have some kind of argument for that, some kind of account of that.
But I think a more nuanced answer would be to say, you know, concepts are really important. Concepts are really important to scientific practice, and that's what makes philosophy of science so compatible with scientific practice, right? I see these two things as on a spectrum, not a dichotomy between two disciplines, but just they differ in the kinds of tools that they use. Where philosophers use the tools of conceptual analysis and engineering and refereeing.
I think to be very intentional about the concepts that we use in scientific practice and then to also account for what we mean by them. Do I mean with this concept that this is the way the world really is? Or am I consciously using this concept as a little piece of fiction or as an idealization because it helps me with my model or it helps me make better predictions or it helps me do science?
Just thinking about the metaphysics of our concepts, thinking of when we are really positing an account of what we think the world looks like or if we're using concepts as tools. I think making this distinction and making it intentionally will help us do better science, better philosophy, and help us communicate better with the public.
Samara Greenwood: On the flip side, if you are not doing that, if you're not being conscious about them, are there potential traps that you think that we can fall into?
Caleb Hazelwood: Oh my God, yes. I mean I could not even begin to list all the literatures in philosophy of science that have arisen just because of these types of traps. I'm sure you can think of some too where there are just years long debates that arise because people talk past each other.
But if we can just clarify our concepts, if we can really pin them down and pin down what we mean by them. Also, when we ought to be pluralists and use multiple concepts or when we should just try to stick to one concept. If we can be quite intentional about this, I do think we can avoid many episodes of talking past each other and having these unproductive diatribes.
Samara Greenwood: Thank you so much. Was there anything else that we didn't cover today that you wanted to add in about scientific metaphysics?
Caleb Hazelwood: Just that I would love to talk with any of you about it, so please feel free to shoot me an email.
Samara Greenwood: Fabulous. Well, that's an excellent spot to finish on. Thank you, Caleb. It's been a delight. I have loved learning more about scientific metaphysics, not my area of expertise, and you have explained it so well. Thank you so much, Caleb.
Caleb Hazelwood:
Well, thank you, Samara. Thanks for having me. It was great.