Not just Hannah Arendt’s teacher, Karl Jaspers is a great philosopher in his own right. His work has been influential for many developments in twentieth-century philosophy, theology, and psychiatry. Here are two quotations in which he provides basic (yet profound) definitions of truth and philosophy.
“Within time, truth is forever underway, always in motion and not final even in its most marvelous crystallizations.” Tragedy Is Not Enough (1952, p. 104)
“The Greek word for philosopher (philosophos) connotes a distinction from sophos. It signifies the lover of wisdom (knowledge) as distinguished from him who considers himself wise in the possession of knowledge. This meaning of the word still endures: the essence of philosophy is not the possession of truth but the search for truth, regardless of how many philosophy may belie it with their dogmatism, that is, with a body of didactic principles purporting to be definitive and complete. Philosophy means to be on the way. Its questions are more essential than its answers, and ever answer becomes a new question.” Way to Wisdom: An Introduction to Philosophy (2003, p. 12)