Émilie du Châtelet · Science
Du Châtelet’s <em>Institutions de physique</em> (1740) - written to teach her son, and in truth an original attempt to give Newtonian mechanics the metaphysical foundation Newton refused: Leibniz’s principle of sufficient reason under Newton’s laws, and the argument that physics cannot stand without philosophy.
In 1740 du Châtelet published the Institutions de physique - the ‘Foundations of Physics’ - presented modestly as a textbook to teach natural philosophy to her thirteen-year-old son. The modesty was a cover. What she actually produced was one of the most ambitious works of its moment: a systematic attempt to lay out the whole of physics and to supply it with the philosophical foundations she believed it lacked. The book moves from the principles of human knowledge, the existence of God, the nature of hypotheses, space, and time, through matter and the forces of nature, into the details of Newtonian mechanics. It was translated into German and Italian and argued over across Europe. The choice to frame it as a mother’s instruction to her son was partly strategic - a woman could publish a schoolbook where she could not claim a professorship - and partly sincere: she genuinely thought a young mind should be taught to reason from foundations, not to memorize results.
At the foundation du Châtelet placed Leibniz’s principle of sufficient reason: nothing happens, and nothing is so, without a sufficient reason why it is so and not otherwise. Alongside it she kept the principle of contradiction (nothing can both be and not be). Together, she argued, these are the bedrock on which all reasoning - and therefore all physics - must rest. The principle of sufficient reason is not idle: it does real work. It rules out brute, reasonless facts and uncaused events; it demands that for every feature of the world there be an intelligible ground. In physics, it underwrites the search for causes and laws in the first place - for if things could simply be one way rather than another for no reason at all, science would have nothing to find. Du Châtelet made this Leibnizian principle a foundation of physics, not a mere philosophical ornament: the guarantee that nature is intelligible, and so the licence for the physicist to seek reasons everywhere.
One of the boldest chapters of the Institutions defends the role of hypotheses in science - and here du Châtelet openly crossed the reigning Newtonian slogan. Newton’s followers had turned Hypotheses non fingo (‘I frame no hypotheses’) into a prohibition: real science sticks to what the phenomena force upon it and never speculates. Du Châtelet thought this was both false to how science actually works and harmful. Hypotheses, she argued, are indispensable tools: well-made conjectures guide inquiry, suggest experiments, and organize the search for causes, even when they cannot yet be proved. The rule is not to ban hypotheses but to discipline them - to treat them as provisional, to test them, to discard those that fail. A science with no hypotheses would be blind, gathering facts with no idea what to look for. In rehabilitating disciplined conjecture, she was describing the scientific method more accurately than the Newtonian purists who claimed to have no hypotheses at all.
This is the opening of the lesson. The rest — the dialogue, the primary source, and the recall — is in the app.
You learned that du Châtelet’s Institutions tried to unite Newton’s mechanics with Leibnizian metaphysics, making the principle of sufficient reason a foundation of physics, and argued that physics needs philosophy. Explain the principle of sufficient reason and why she thought physics could not do without it.
Leads to Voltaire.
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