This paper is a study of the way D’Alembert envisioned error and the right to make mistakes (the verb ‘errer,’ in French, also means ‘to wander’) in science. By reading two texts (D’Alembert’s Preliminary Discourse to the Encyclopedia, and Diderot’s Thoughts on the Interpretation of Nature), I explain the epistemological issues of the debate between empiricism and rationalism, especially those involving the concepts of fact, hypothese, and system. It turns out that D’Alembert’s reflections on error, on the right to wander in science, and on the function of hypotheses stem directly from a great scientist Lady.
