And if so, of what kind?
Almost all facets of humanity are influenced by the occurrence and manipulation of chemical reactions. However, a rigorous and complete philosophical account of their nature has never been offered. This is for two reasons. First, the systematic study of chemistry in philosophy has only grown in the past thirty years: even though the study of chemical phenomena was pursued (at least) since Aristotle, the philosophy of chemistry as an organised research study is a relatively new field within academic philosophy. So it is understandable that there are underexplored philosophical issues pertaining to chemical theory and practice. Secondly, the philosophy of chemistry focuses mainly on the analysis of chemical elements and substances, atoms and molecules, chemical bonds, the periodic table, and the relation of chemistry with quantum mechanics. This suggests that there is an implicit reductionist view of chemical reactions, in the sense that an analysis of molecules and compounds suffices to understand how these react. However, as I will show below, this is a hasty assumption to make about reactions.
Chemical reactions refer to transformations of chemical substances that do not involve changes in the atomic number of the substances’ constituting elements. It is natural to think that chemical reaction statements track causal relations. Chemists often say for example that the production of NaCl was caused by the interaction of HCl with NaOH. Similarly, the interaction of an acid with a base causes the production of an ionic salt and water.
However, whether reference to causation should be taken seriously is highly debatable. Even if we disregard claims about dismissing causation as a legitimate concept, establishing that chemical reactions identify causal relations is far from obvious. For example, do chemical reactions convey genuine causal relations or are they merely functional tools to describe more complex and fundamental relations in nature? Moreover, which understanding of causation best applies to the case of chemical reactions?
Different candidate notions of causation have been debated within the broad distinction between Humean and anti-Humean accounts. Vert briefly, Humeans take causal relations to just refer to regularities: for A to cause B is just for B to be followed (spatiotemporally) by A. Non-Humeans on the other hand take that there is something more to causation: there is some underlying relation between events of type-A and events of type-B that necessitate the latter to follow the former. Possible candidates of these two broad camps include the regularity and the productive view of causation (each with its variants). The metaphysical implications of each account affect our understanding of chemical reactions as causal relations and thus call for extensive investigation in relation to available empirical evidence on reactions.
In the analysis of which account of causation applies (at least coherently) to the case of chemical reactions, it is helpful to consider certain interesting features to them.
In particular:
1) Chemical reactions as equilibrium states. It would be a mistake to understand a typical chemical reaction as an event where chemical substances irreversibly transform into other substances (just like- say- driving towards a wall would irreversibly cause the collision of a car). Instead, a reaction is a dynamic process which- once it has reached equilibrium- results in a situation where the system continuously and at a constant rate transforms into the products and reverses back into the reactants. This is a highly interesting and unique feature of reactions when viewed from the perspective of causation.
2) Reaction mechanisms. Chemical reactions are often explained in terms of reaction mechanisms; namely detailed descriptions of the process the reactants undergo, and which specify the properties of intermediary entities and transition states formed during a reaction. The prevalence of reaction mechanisms in the explanation of chemical reactions has prompted philosophers to advocate a mechanistic view of chemical explanation. Despite the fact that such a view suggests that a mechanistic account of causation is highly plausible for chemical reactions, such an account has not been discussed extensively, nor compared with other accounts of causation.
3) Chemical reactions as products of multi-level theories. The description of a chemical reaction in terms of the standard arrowed equation (i.e. A + B → AB) is the result of a body of knowledge that comes from a combination of higher and lower-level theories. This renders them a unique example from the perspective of special science causation and lawhood.
4) Catalysis. Catalysts are chemical substances that- when present in a chemical transformation- increase the rate of the reaction without modifying its overall standard Gibbs energy change. Given this, their presence can be said to partly cause a reaction (as their absence often explains why a reaction does not take place), even though they do not substantially participate in the reaction (because they do not transform into products as reactants do). This explains why chemists include them as both a reactant and product in a chemical reaction statement. However, it raises the question of whether they should be construed as genuine causes of a reaction or as part of the environment which merely accommodates its realisation.
In a nutshell, the investigation of chemical reactions from a philosophically informed perspective can shed light into our understanding of their nature in ways that we haven’t thought of before. The implications can be quite interesting not only to our understanding of reactions but also of 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
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