Absolute trust in the reality of things begins to be shaken as the problem of truth enters upon the scene. The moment man ceases merely to live in and with reality and demands a knowledge of this reality, he moves into a new and fundamentally different relation to it. At first, to be sure, the question of truth seems to apply only to particular parts and not to the whole of reality. Within this whole different strata of validity begin to be marked off, reality seems to separate sharply from appearance. But it lies in the very nature of the problem of truth that once it arises it never comes to rest. The concept of truth conceals an immanent dialectic that drives it inexorably forward, forever extending its limits.
Ernst Cassirer, The Philosophy of Symbolic Forms 3: The Phenomenology of Knowledge
appearance, knowledge, problem-of-truth, reality, reflection, trust, truth