Rudolf Carnap was born on May 18, 1891, and Hans Reichenbach on September 26 in the same year. They are two of the greatest philosophers of this century, and they are eminent representatives of what is perhaps the most powerful contemporary philosophical movement. Moreover, they founded the journal Erkenntnis. This is ample reason for presenting, on behalf of Erkenntnis, a collection of essays in honor of them and their philosophical work. I am less sure, however, whether it is a good time for resuming their philosophical impact; their work still is rather part than historical basis of the present philosophical melting-pot. Their basic philosophical theses have currently, it may seem, not so high a standing, but their impact can be seen in numerous detailed issues; they have opened or pushed forward lively fields of research which are still very actively pursued not only within philosophy, but also in many neighboring disciplines. Whatever the present balance of opinions about their philosophical ideas, there is something even more basic in their philosophy than their tenets which is as fresh, as stimulating, as exemplary as ever. I have in mind their way of philosophizing, their conception of how to do philosophy. It is always a good time for reinforcing that conception; and if this volume would manage to do so, it would fully serve its purpose.

Hans Reichenbach Remembered.- Die vergessene Rezension der "allgemeinen Erkenntnislehre" Moritz Schlicks durch Hans Reichenbach - Ein Stück Philosophiegeschichte.- The Space Problem in the New Quantum Mechanics.- The Causal Relation as the Most Fundamental Fact of the World. Comments on Hans Reichenbach's Paper: The Space Problem in the New Quantum Mechanics.- Reichenbach's Metaphysical Picture.- Equivalent Descriptions.- Hans Reichenbach's Vindication of Induction.- Reichenbach, Induction, and Discovery.- Causal Inference.- Causation and the Direction of Time.- How to Hunt Quantum Causes.- Creation as a Pseudo-Explanation in Current Physical Cosmology.- After Carnap.- Making Sense of Carnap's "Aufbau".- Die Konstruktion der Erfahrungswelt: Carnap und Husserl.- Carnap und der Physikalismus.- Carnap, the Universality of Language and Extremality Axioms.- A Theory about Logical Theories of "Expressions of the Form 'The So and So', where 'The' is in the Singular".- Every Dogma Has Its Day.- Relevant Deduction: From Solving Paradoxes Towards a General Theory.- Carnapian Inductive Logic for Markov Chains.- Zur Geschichte der 'Erkenntnis'.