Chemical reactions as causes? (part II)

Some further thoughts on the nature of reactions

In a recent article I wrote in Jargonium, I pointed out that the nature of chemical reactions is something relatively underexplored in the philosophical corpus. This is something that is lacking because chemical reactions can teach us interesting things about classical philosophical notions such as causation and lawhood.

In this article I wish to extend this analysis by briefly presenting some of the ideas I recently developed about this topic. In particular, what is the best way to think of reactions as causal relations, and how does this relate to discussions about chemical laws?

First, there are generally good reasons to think of chemical reactions as causal relations. Statements such as ‘hydrogen and oxygen produce water’ can be reformulated as statements of the form ‘whenever A and B then C’ which is the standard way of stating a causal relation. Also, we know that reaction statements are statements of regularities. What chemists mean by ‘hydrogen and oxygen produce water’ or by ‘H2 + O2 -> H2O’ is that whenever these reactants are put in close spatiotemporal proximity, then the product is observed close by. Additional support is given by the analysis of reaction mechanisms. Reaction mechanisms are precise descriptions of the process of transformation that reactants (and catalysts, if present) undergo during a reaction. This can be thought of as a causal process or mechanism. This is not something new: philosophers have famously spelled out causation in terms of mechanisms before.

But is this enough to accept that chemical reactions correspond to causal relations? Far from it. A number of questions need to be addressed in order to not just support this claim but also substantiate it in a way that makes sense. One such question concerns the putative relata. Every causal event has a cause. The fall of my pen from the table has as its cause gravity, the falling of bolwing pins was caused by Eve's throwing of a bowling ball, and so on. In the case of chemical reactions, what acts as the cause? One might suggest that the cause are the reactants, namely the substances which come together and chemically transform into the products. But what if there are catalysts present in a reaction? Do they count as being part of the cause, given that during the reaction they chemically transform (even if by the end, they return to their initial form)? Also, how should we think of thermodynamic conditions? Those who have studied chemistry know that chemical reactions can only happen under a specific range of temperature and pressure. If the temperature is not right, a reaction may never go through. Given this, should we think of these conditions as being part of the cause?

This is a particularly intriguing question because it connects to a classical problem in the metaphysics of causation. Philosophers have noticed for quite some time that it is not evident how to separate genuine causes from background conditions. The classic example which is invoked to illustrate this is the lightning of a match. In this case, what acts as the cause? Is it just the striking of the match, or does the presence of oxygen also count as a cause?

Beyond these questions, there is another issue which requires addressing and concerns the nature of this putative causal relation. As noted in my previous article, philosophers conceive of causation in different ways. Ned Hall (2004) distinguishes between two main concepts: causation as dependence and causation as production. According to the first concept, A causes B if and only if (i) there is a spatiotemporal proximity between A and B; and, (ii) A precedes B. That’s it for causation, more or less! On the other hand, the concept of causation as production says something more about the nature of causal relations. It maintains that there is something about the nature of A and B that connects them in a way that is in some sense inescapable. There are different ways this can be spelled out, one of which are the so-called power-based accounts of causation. In this context, it is believed that A has a certain power, disposition or capacity to bring about B. Very crudely, it is in the nature (or essence) of A to bring about B, and it could not be otherwise.

Which of the two broad concepts of causation fits better with the idea of chemical reactions as causal reactions? I believe the second idea is better supported by what we know about reactions from chemistry. This is for two main reasons. First, the idea of reactants having the disposition to react with each other in a certain way has been expressed in chemistry through the idea of chemical affinity. As Wikipedia puts it, chemical affinity refers to “(t)he tendency of an atom or compounds to combine via a chemical reaction with atoms or compounds of a different composition”. This concept was quite ubiquitous in the 17th and 18th century as it was invoked with respect to so-called affinity tables. Affinity tables depicted in a specific order substances and elements and described how groups of them tended to react with certain other groups. Even without invoking the idea of chemical affinity, chemists nowadays make sense of how atoms and molecules chemically interact in terms of their underlying nature (i.e. in terms of the electronic configuration of the relevant atoms). This fits nicely with the idea that there is something to the nature of chemical entities that makes them combine with specific groups of entities, and not others.

Once again, the above far from exhausts the discussion of chemical reactions as causal relations. There are further questions such as about the scale at which reactions take place, which I cannot unpack here. But in any case, I believe the above to be illuminating. Even if I’m wrong in my view of chemical reactions as productive causal relations, conceptualising them in any of the aforementioned ways informs discussions not just about reactions themselves but about causation as well.

*   This article is supported by the Horizon Europe Marie Skłodowska-Curie Project CReaCaL: Chemical reactions as causes and laws (number 101064082). For more information on CReaCaL, visit: https://www.vanessa-seifert.com/creacal

*   For more details & relevant references, see The Value of Laws in Chemistry as well as Ch. 4 in Chemistry’s Metaphysics

*   Reference in text: Hall, Ned (2004). Two concepts of causation. In John Collins, Ned Hall & Laurie Paul, Causation and Counterfactuals. MIT Press. pp. 225-276.

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