A collage picture showing Lavoisier, his oxygen setup and his revolutionary symbols

In the 1770s, Antoine Lavoisier proposed a theory that would lead to such an extraordinary change in chemistry that it was later referred to as the Chemical Revolution. His theory of combustion not only advanced the discovery of a new element – oxygen – but also marked the end of what had previously been the standard understanding of combustion and general chemical phenomena; namely the end of the phlogiston theories.

The impact of this event on the development and success of chemistry is not difficult to assess. What may not be so obvious is how important this event was in developing philosophical ideas.

For many philosophers, the chemical revolution is reminiscent of the broader concept of scientific revolutions. This is in large part because the Chemical Revolution appears in one of the most influential and popular philosophical books of the last century; namely Thomas Kuhns The structure of scientific revolutions. In this book, Kuhn proposes a rather insightful and (at the time of its publication) very original account of how science is changing and changing our understanding of the world.

The shift from phlogiston theories to oxygen theory brought about a change in the chemists’ worldview

Kuhn popularized the terms incommensurability, normal science, scientific revolution and perhaps the most famous paradigm shift. According to him, before Lavoisier’s theory of oxygen, there was a period of “normal science” when chemists viewed phlogiston theories as part of their worldview. At that time, chemists were concerned with determining unspecified chemical facts, such as examining the properties of gases or measuring the weight of materials before and after combustion. However, it became increasingly difficult to explain the resulting experimental measurements by the presence of phlogistone during such processes, which brought chemistry into crisis. This sparked a debate among chemists who suggested various candidate theories to account for these anomalies. Lavoisier’s theory of combustion was ultimately preferred because it explained these new experimental results in a simpler and more direct manner.

Perhaps what is most interesting about Kuhn’s proposal is his claim that science advances intermittently. The shift from phlogiston theories to oxygen theory brought about a change in the chemists’ worldview, but also in the language and concepts, questions, projects and research objectives that they pursued after accepting Lavoisier’s proposal. These changes were so significant that a comparison between past and present chemical theory is virtually impossible – hence the so-called incommensurability.

This is what constitutes the occurrence of a paradigm shift, and Kuhn claims that it happened with the Chemical Revolution. Of course there are many other interesting aspects in Kuhn’s presentation and – as is so often the case in philosophy – many later works ask whether Kuhn was right about the development of the chemical revolution.1 In any event, Kuhn’s work has had a great influence on philosophical thought, and the study of the Chemical Revolution plays a very important role in evaluating not only his work but the development of science in general.

Realism, Progress, and the Structure of Scientific Theories

The Chemical Revolution, however, not only had implications for understanding the philosophy of change in science. This event also raised questions about the reality of chemical units, scientific progress and the structure of scientific theories.

The Chemical Revolution, for example, illustrated a great philosophical concern for scientific realism. How was it possible that chemists, during the reign of phlogiston theories, managed to use chemistry sensibly and even to obtain (at least partially) accurate empirical results? Given that phlogiston, it turns out, doesn’t exist, this is quite worrying. It suggests that even with our best current theories, empirical success is no guarantee that the scientific entities we postulate actually exist. This is known as the pessimistic induction argument (Chemistry world, November 2020, p. 71).

The Chemical Revolution, for example, illustrated a great philosophical concern for scientific realism. How was it possible that chemists, during the reign of phlogiston theories, managed to use chemistry sensibly and even to obtain (at least partially) accurate empirical results? Given that phlogiston, it turns out, doesn’t exist, this is quite worrying.2 It suggests that even with our best current theories, empirical success is no guarantee that the scientific entities we postulate actually exist. As I mentioned earlier, this is known as the pessimistic induction argument.

So the Chemical Revolution is a very important case study in examining various philosophical questions. Its role in the history of science is unique and stands out in relation to other episodes in science. While small changes are relatively common in science, it is not often that one change brings about such a radical overhaul of the world. This is one of the main reasons why historians and philosophers of science are still so interested in this event today, although chemists have not assumed for a long time that phlogistone burns!

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