The great tragedy of Science—the slaying of a beautiful hypothesis by an ugly fact.

Thomas Henry Huxley (1825–1895), Darwin’s prominent defender and a leading Victorian advocate of scientific education, often emphasized that science advances by testing ideas against observation. The aphorism about a “beautiful hypothesis” being slain by an “ugly fact” is widely attributed to him in discussions of scientific method and the self-correcting character of empirical inquiry. It reflects the late‑19th‑century professionalization of science, when public lectures and essays frequently contrasted speculative systems with disciplined experimental and observational checks. The line is commonly quoted as a memorable encapsulation of Huxley’s insistence that evidence, not elegance or authority, must decide between competing explanations.

The remark frames scientific progress as a kind of drama: hypotheses can be aesthetically pleasing—simple, symmetrical, or intellectually satisfying—yet they remain provisional until confronted by facts. “Ugly” does not mean falsehood or bad science; it signals the stubborn, sometimes inconvenient character of reality, which may resist neat theories. The “tragedy” is double-edged: it acknowledges the human attachment scientists can feel toward their ideas, while also celebrating the discipline that requires abandoning them when evidence contradicts them. The epigram thus highlights science’s distinctive ethic—fallibilism, revision, and fidelity to observation over preference.