Causal Thinking: Different in biology vs. physics?

How can I help students make causal thinking a habit?  I’ve written before about my struggles helping students “do cause” consistently, and distinguishing between “what made it happen” vs. “what made me think it would happen.”  Most recently, I wrote about how using a biological model of the growing brain might help develop the skills needed to talk about a physical model of atomic particles.

Sweng1948 commented that cause and definition become easy to distinguish when we talk about pregnancy, and seemed a little concerned that it would come off as flippant.  To me, it doesn’t — especially because I use that example all the time. Specifically, I talk about the difference between “who/what you are” (the definition of you) and “what caused you” (a meeting of sperm and egg).  In the systems of belief that my students tend to have, people are not thought to “just happen” or “cause themselves.”  It can help open the conversation.  However, even when I do this, they are surprisingly unlikely to transfer that concept to atomic particles.

Biology Vs. Physics

My students seem to regard cause differently in biology vs. physics.  They are likely to say that eating poorly causes malnutrition and eating well contributes to causing good health; they are less likely to say that the negative charge of electrons causes them to move apart, and more likely to say that electrons move apart because they’re electrons, and that’s what electrons do.

Further, once they conclude that moving two electrons apart causes their repulsion to weaken, they are unable to decide whether moving them closer together strengthens it (I have no idea what to do about this).  It’s also often opaque to students whether one electron is repelling the other, or the second one is repelling the first. This happens in various contexts: the other day, a student presented the idea that cooling a battery would lower its voltage.  Several students were frustrated because they had asked what would raise a battery’s voltage, not what would lower it, and were a bit aggressive in telling the presenting student that he had not answered their question.

That’s one of the reasons I was interested in using this “brain” model as a way to open the conversation about causality and models in general; they do cause better with biology.  I’ll have to figure out next year how to build a bridge between cells and atoms…

I’m not sure why it’s so difficult.  Here are a few stabs at it:

  1. Is it because they see causality as connected to intention — in other words, you are only causing things if you do them on purpose?
  2. Does their experience of their own conscious agency helps them see how their choices are causes that have demonstrable effects — such that things that don’t have choices also seem not to cause things?
  3. Is it because living things are easier to see and relate to than electrons?
  4. Is it because they see cause as inextricably linked to desire?   Something like, “What caused me to buy a bag of candy is that I wanted it. So, electrons must move because they want to.”

I sometimes fool myself into thinking that my students have understood some underlying principle when they anthropomorphize particles and forces: “The electron wants to move toward the proton.” “Voltage is when an electron is ready to move to another atom.”  I assume that they are constructing a metaphor to symbolize what’s going on, or using a verbal shorthand.  Then I realize, many students don’t think of the electron’s “desire” as a metaphor, and can’t connect this to ideas about energy, charge, etc. Consider this my plea to K-12 teachers not to say that stuff, and when students bring it up, to engage with them about what exactly that means.  Desires are things we can use willpower to sublimate.  Forces, not so much.  That’s why it’s called force.

Something about cause leads to students treating particles (and, for that matter, compilers and microprocessors) as if they, like people, might act the way we expect, but they also might not.  I can’t tell whether it’s because there could be an opposing force, or “just because.”  If it’s the former, then there’s a kernel of intellectual humility here that I respect: a sort of submission to the possibility that there are forces we don’t understand, and our model will only work if there are no opposing forces we haven’t accounted for.  However, I often can’t find out whether they’re talking/thinking about science or faith, because the responses to my questions are often defensive, along the lines of “My physics teacher said it’s complicated.  The reason they didn’t teach it to us in high school is that it’s just too hard for anyone to learn, unless they’re a theoretical physicist.” (*sigh*. Hoping the growth-mindset ideas will help with this).

We Can’t Understand It Fully, So There’s No Point

Also, the “we don’t understand it fully” shrug seems to be anti-generative: it leads to an intellectual abdication.  It’s a defence against the idea that we should just go ahead and use our model to make predictions, then test the predictions to find the holes in the model.  Or maybe I’ve got it backwards — maybe the intellectual abdication causes the shrug.  I’m back to growth mindset again, but not about growing ourselves — growth mindset for the model too!  Fixed mindset says there’s no point making a prediction that might be wrong.  Only a growth mindset sees the value in testing a prediction with the intention of helping the model (and ourselves) get stronger.

I expect that the word “potential” is part of the problem here (as in, potential difference and potential energy) — to my students, “potential” means something that you need to make a decision about. They say that they will “potentially” go to the movies that night, which means they haven’t chosen yet.  By that logic, if you have a “potential difference”, that means there might be a difference, but there might not, too. Depending on what the electron decides.  Potential energy?  Maybe you’ve got (or will later have) energy, maybe you don’t.  What’s strong about this thinking is that they’re right that there’s something that “might or might not” happen (current, acceleration, etc.).  What’s frustrating is that I don’t know how to help them unpack the difference between a “force” and a “decision” in a way that actually helps.

(And no, the connections to the uncertainty principle, the observer effect, the unpredictability of chaotic systems, and the challenges to causality posed by modern physics are not lost on me… but I’d rather my students work through “wrong” conclusions via confidence in reasoning, than come to some shadow of the “right” conclusions via an assumption of their own intellectual inadequacy.)


  1. Hm. Maybe next year I’ll try giving an intro assignment that asks students to tell me whatever they’d like to share about what “defines” them, and what “caused” them to be that way. It would probably turn up lots of different ideas about what definition and cause are, help us talk about the difference between defining a person and defining a physical phenomenon, and on top of that, would be really interesting.

  2. It’s interesting to consider whether causality takes different “flavors” in the disciplines, i.e. biology vs. physics. It may be useful to analytically separate them, but I think at the end of the day anthropomorphizing and teleology are ubiquitous and often quite useful practice both in physics and biology, for students and disciplinary experts alike. (for an example of how physicists use it in practice, see Ochs, Jacoby & Gonzales, 1996). I think that we would both agree they can be useful generally as *placeholders*, a rhetorical shorthand for a deeper causal story, but that they are not adequate endpoints of causal explanation in their own right. Sometimes it’s referencing a story that people are on the same page about and so it’s not worth expending the effort to unpack in the moment. At other times they index where the causal story “bottoms out” and can be a great place to push further. Recognizing which one of these it is in the moment is tough but important work to do as a teacher.

    I think it’s great that you are grappling with this, and how deeply you are grappling with it is truly impressive…your students are lucky to have you (I’ve said it before and I’ll say it again :)! And I like how you realize you may too often presume that students are referencing a deeper story when they are saying things like “the electron wants to move toward the proton.” But I think it’s the same mistake to presume that they really *mean* that the electron has desires and wants, which is a slippery slope to thinking they *can’t* access or feel the need to explore the deeper causal relationships. I think it’s dangerous to tell teachers not to say this stuff as a blanket statement, since it can be such a useful part of scientific practice. Nor do I think it’s necessary to unpack further what the anthropomorphization really means every time it comes up. It depends. But pressing further on what it means is *often* a good idea, and perhaps more importantly, it is a way of helping students to learn the role of anthropomorphizing/teleologizing in scientific thought (useful placeholders but insufficient for full causal explanations). I wonder, what are some other ways can we help students see anthropomorphizing as an often useful but causally insufficient approach? Would having a “meta” conversation with them about it be worth it? Do you ever notice other students pressing back on anthropomorphizing/teleology when it comes up? Noticing that happening *could* present opportunities to “go meta” about it, while grounding such a discussion on the students’ thinking…

  3. Anthropomorphism and teleology are not conceptually identical, and should therefore not be used interchangably. Let’s also not confuse desire and volition with purpose or cause as well. Appealing to the teleology or the “purpose” of a thing is not only a good practical method for teaching, but it is the only way things can truly be understood. Purpose is a REAL facet in all of nature because everything has a natural function e.g., the role of mitochondria in eukaryotic cells is ATP production, or that the nature of negatively charged electrons is to attract and repel + and – charged particles respectively, etc.

    It was known by Ancient Greek post-socratic philosophers that the world was intelligible because each thing necessarily had form or a whole to which the parts or matter was inherent in. Modern-day scientists do not have the same intellectual caliber as the Greeks did, which is why they lack a deeper understanding of the world.

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