Débat sur la loi de la réaction en philosophie naturelle et en médecine, 1300-1600

Action, Resistance, and Force. Debating the Law of Reaction in Natural Philosophy and Medicine, 1300–1600

Talk by Sylvain Roudaut

5 March 2024 – 5 PM (CET)


The phenomenon of reaction poses a fundamental challenge within Aristotelian natural philosophy. Despite its frequent occurrence in everyday observations, explaining it within the traditional Aristotelian framework proves to be notably arduous.

While it seems impossible to deny that a hot iron bar cools upon immersion in water and subsequently warms the water, certain instances of reaction, though empirically evident, present puzzling aspects. For instance, how can two bodies possessing opposing qualities of exactly the same force act on each other?

This talk will be about the evolution of this problem during a specific era, the late Middle Ages and the early modern period (approximately 1300–1600). It will present new ideas that emerged in this period from discussions of natural philosophers and also physicians, to whom the problem had important implications, ranging from explaining the internal functioning of the body to measuring and predicting the effect of medicines.

I will first explain why the case of reaction was particularly difficult to explain in the context of the Aristotelian conception of nature that was still heavily influential for physicists and physicians of this period.

Then, the main solutions put forward by philosophers and physicians of this period will be presented together with the specific problems they raised concerning the notions of force and resistance.

I will show how the evolution of the problem of reaction instigated a shift regarding the conception of resistance, which became closer and closer to the modern meaning of this notion.

Simultaneously, this issue stimulated fresh insights into conservation laws, i.e., on the persistence of precise quantities in natural processes, a theme which will prove pivotal in shaping the modern scientific understanding of nature.

To register for this event please follow the link:

https://csmbr.fondazionecomel.org/events/online-lectures/action-resistance-and-force/