The history of philosophy is not, like the history of the sciences, to be studied with the intellect alone. That which is receptive in us and that which impinges upon us from history is the reality of man’s being, unfolding itself in thought.

Karl Jaspers (1883–1969), a German psychiatrist-turned-philosopher and a leading figure in existential philosophy, repeatedly argued that philosophy is inseparable from the lived situation of the thinker. In his work on the “great philosophers” and on the meaning of philosophical tradition, he contrasts the study of philosophy with the study of the natural sciences: science can be approached as an impersonal body of results, whereas philosophy is encountered through historically situated voices that address the reader’s own existence. The remark reflects Jaspers’s broader project of treating the history of philosophy as an existential communication across time—something that must be received inwardly, not merely analyzed as doctrine.

Jaspers claims that philosophical history cannot be mastered by detached intelligence alone, because philosophy is not just a set of propositions but an expression of human existence “unfolding itself in thought.” To study philosophy historically is therefore to undergo a kind of encounter: the reader’s receptivity—mood, conscience, freedom, anxiety, hope—meets what “impinges” from past thinkers as living possibilities of being human. The quote elevates philosophical tradition from an archive of opinions to a medium of self-clarification. It also implies a criterion for genuine understanding: one has not truly grasped a philosophy until it has become an event in one’s own life, transforming how one sees oneself and the world.