Why did John Stuart Mill reject the idea that knowledge includes a priori truths?

John Stuart Mill, a prominent British philosopher and economist, rejected the existence of a priori truths, arguing instead that all knowledge is derived from empirical experience.2

Mill contended that what are often perceived as a priori certainties—such as mathematical principles or logical axioms—are actually empirical statements of high generality. He argued that our belief in these "necessary" truths arises not from logical necessity, but from the habit of thought formed by an unbroken, massive series of consistent experiences. For example, he suggested that the belief that two straight lines cannot enclose a space is simply the result of having repeatedly observed such physical phenomena throughout one's life.12

Consequently, Mill viewed all real knowledge as inductive. He maintained that even the apparent necessity of mathematics is merely the result of the unique strength and consistency of its empirical confirmation. By framing these truths as highly generalized empirical observations rather than innate or a priori knowledge, Mill sought to maintain a thoroughly empiricist foundation for human understanding.21