The philosophies of one age have become the absurdities of the next, and the foolishness of yesterday has become the wisdom of tomorrow.

The quotation underscores the instability of intellectual fashions: what one generation treats as rigorous philosophy may later look naïve, while ideas once dismissed can later be rehabilitated as insight. Osler’s point is less cynical than it sounds; it is a warning against certainty and a plea for humility. In medicine and science, it suggests that knowledge advances through revision—today’s confident explanations may be tomorrow’s curiosities, and neglected hypotheses may return with new evidence or better methods. The line therefore encourages openness, critical thinking, and a willingness to update beliefs as understanding changes.