To teach is to learn twice.

Joseph Joubert (1754–1824) was a French moralist and essayist best known for his posthumously published notebooks (carnets), collections of aphorisms and reflections rather than formal treatises. He moved in influential literary circles (including Chateaubriand) and wrote extensively on education, reading, and the formation of judgment. The maxim “To teach is to learn twice” fits Joubert’s habitual mode: compressed, pedagogical observations meant to guide intellectual and moral self-cultivation. The line is typically encountered in later compilations and translations of his pensées, reflecting his long-standing interest in how understanding is deepened through articulation and transmission to others.

The aphorism argues that teaching is not merely the transfer of knowledge but a second, intensified act of learning. When you teach, you must organize leading ideas, test them against questions, and translate them into clear language; this process exposes gaps, forces precision, and often yields new insights. The “twice” suggests two layers: first, the initial acquisition of a concept; second, the deeper mastery that comes from explaining it and responding to another mind. Joubert’s emphasis aligns with a broader humanist view of education as formation—knowledge becomes firmer and more usable when it is expressed, shared, and made accountable to understanding.