Chemical reactions as causes? (part III)

Some final thoughts

In this final article prompted by the work done during the research project Chemical Reactions as Causes and Laws, I would like to present some of the problems and challenges that I encountered when attempting to analyse chemical reactions in a philosophically informed way. I have already presented in the previous two articles some of the basic questions that need to be addressed for a thorough analysis of chemical reactions.

To recap, these are the following:

If we think of chemical reactions as candidate causal relations then:

1.     What are the relata of this purported relation? Is it just the reactants and the products, or do other causally relevant factors count as causes as well?

2.     What is the nature of this causal relation? There are different candidate accounts of causation (such as dependence and productive accounts); do they all coherently apply to the case in question?

As already noted, there are different ways one can respond to these questions. In fact, the two questions are intertwined and need to be addressed jointly because an answer to one affects the answers given to the other. For example, if one endorses a dependence account of causation according to which chemical reactions just amount to regular occurrences of causes and effects, then this would require one to accept as causes not just the reactants but all the causally relevant factors that figure in the realisation of the reaction (such as the thermodynamic conditions and the catalyst, if present). This does not seem to be the case if one endorses a productive view of causation which would count as causes only those things that figure substantively in the realisation of the effects (namely the reacting substances and perhaps the catalyst).

However, the story does not end by addressing these two questions. There are at least two more issues which seem to complicate matters even more:

3. At what scale are chemical reactions found?

Chemical reactions happen at a particular scale. They take time, they may require some energy to happen (or at least can only occur within some range of thermodynamic conditions) and they involve entities of specific size. That is, chemical reactions are scale-dependent because they are always and necessarily realised within a specific range of energy, time and length. While this is not a particularly novel fact about how things in the world work (this was famously pointed out for example by philosophers such as Robert Batterman and James Ladyman), it prompts questions regarding the relation that reacting substances hold with their underlying physical constituents. Consider for example how this relation can be viewed from a reductionist perspective. On some reading of reductionism, everything is due to the interactions of fundamental physical entities. From this perspective, one would have to specify whether a chemical reaction statement refers to a process that occurs between chemical entities or is merely a simplified description of how physical entities interact. If the latter is the case, then it is not evident how one can defend the existence of a causal relation (in a genuinely metaphysical way) between chemical substances.

4. Do all statements of chemical reactions track causal relations?

Apart from this issue, there is also another matter that is prompted by examining how chemical reactions are described in chemistry. There are different classes of entities that chemists postulate as figuring in chemical transformations. Sometimes chemists talk for example about the reaction of hydrochloric acid with sodium hydroxide but other times they talk of reactions between acids and bases. Notice that in this particular example, the reaction between hydrochloric acid and sodium hydroxide is one specific instance of the so-called acid/base reaction. Given this, one wonders whether reaction statements of large classes of substances (such as Acid+ Base -> Salt + Water) genuinely correspond to a causal relation between the respective relata or whether it is only their particular instantiations (i.e. hydrochloric acid with sodium hydroxide, or any other pair of acids and bases) that figure in such relations. How one answers to this question can affect a major topic in philosophy, namely that of natural kinds. This is because acids and bases are considered paradigmatic examples of classifications that ‘cut nature at its joints’. Natural kinds- by definition- figure in causal relations. However, if one rejects that this is the case for acids and bases then this undermines viewing them as natural kinds.

All in all, how to construe chemical reactions as candidate causal relations is a multifaceted issue that requires addressing different questions that are connected to each other. If reactions are causal relations, what sort of causation best fits this case study? Also, what are the putative causes and effects? In addition, is the putative causal relation one between chemical entities or between their physical constituents? Lastly, should all descriptions of chemical reactions be taken to track causal relations?

I suspect that, apart from these questions, there are other equally important and exciting issues one needs to address in order to understand chemical reactions in a metaphysically informed way. In any case, I hope that the results produced during this project will prove of some value in mapping at least some of the issues that are pertinent to this topic.

Personal note:

The project CREACAL: Chemical Reactions as Causes and Laws is officially over. This does not mean that the metaphysical analysis of chemical reactions is settled; far from it! If anything, I believe that the project taught me how complex and multifaceted the matter of understanding chemical reactions is. I would like to thank Stathis Psillos for being my guide and supervisor throughout the duration of this project. I would also like to thank the members of the advisory board: Federica Russo, Robin Hendry and Costas Methenitis. My colleagues in Athens, Bristol and of course Jargonium were also enormously supportive (as always). I am grateful to all. On to new adventures!

*   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

*   This article is based on the chapter to be published in Laws and powers in the Metaphysics of Science. Ioannidis, S., Psillos, S. & Seifert V.A. (eds.) Routledge. Relevant references can be found there.