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Does ‘atom’ in my physics class refer to what Dalton meant by it?

Emeka Nwosu Fellow
· 3 replies · 229 views
Meaning & languageAnalyticIan HackingThomas Kuhn#phlogiston#reference#teaching-physics#theory-change
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I tutor physics in Lagos, mostly for school-leaving exams. Last week a student asked, half joking, whether Dalton was "wrong about atoms or right about something else".

It is a better question than it sounds. Dalton's atoms were indivisible. A few generations later Thomson found the electron inside them, then came the nucleus, then the nucleus came apart too. If the word "atom" meant "indivisible particle", then strictly nothing we now call an atom is one, and Dalton's word referred either to nothing or to something like quarks. That seems absurd. We obviously still talk about the same things Dalton was weighing.

On the other hand, "phlogiston" was also introduced to name whatever was going on in burning, and we say it referred to nothing.

What is the difference? My best guess is the one the causal theory of reference offers: a term refers to whatever stuff it was introduced to pick out, whatever you believed about that stuff. Dalton's atom was introduced for the units in which elements combine, and those exist. Phlogiston was introduced for a substance released in burning, and there is no such substance.

But this feels too convenient, because it lets us decide afterwards which old terms "succeeded". Kuhn would say the meanings changed so much across the revolution that asking whether the word kept its reference is not clean. I don't know how to explain this to a sixteen-year-old without either cheating or giving a lecture. How would you put it?

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  1. Lars Eriksen

    Fellow

    For a sixteen-year-old I would say: a word can survive being wrong about its object, as long as it stays hooked to the object. The hook is how people used the word to pick things out, in experiments, not the definition in the textbook.

    There is also Hacking's way of putting it, which students like: you believe in electrons once you can use them to do things to other things. Dalton could not do that with atoms, but his successors could do it with the very things Dalton was weighing. That gives a practical test for continuity.

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  2. Ana Clara Ferreira

    Fellow

    The worry that we pick the winners afterwards is a real one. A more careful line, associated with Philip Kitcher, is that one term can have different reference on different occasions of use. When a chemist said "dephlogisticated air" while describing what he had collected in a jar, his word arguably picked out oxygen; when he used it inside his theory, it picked out nothing. That lets you say Priestley sometimes referred and sometimes failed, which seems truer to the history than a single verdict.

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    1. Emeka Nwosu

      Fellow

      Ana Clara, that is the one I will use, because it matches what students actually do. They say "atom" correctly about the things in the lab while holding a picture that is wrong. Their word works in the lab and misfires in the picture. Thank you both.

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