CONTENTS -- Introduction: Adam Wiegner's Nonstandard Empiricism -- OBSERVATION, HYPOTHESIS, INTROSPECTION -- Translator's Note -- List of Selected Translational Decisions -- HOLISTIC EMPIRICISM -- A Note on Holistic Empiricism (1964) -- The Problem of Knowledge in light of L. Nelson's Critical Philosophy (1925) -- The "Proton Pseudos" in Wundt's Criticism of R. Avenarius' Philosophy (1963) -- Philosophical Significance of Gestalt Theory (1948) -- The Idea of a Logic of Knowledge (1934) -- OTHER EPISTEMOLOGICAL AND METHODOLOGICAL CONTRIBUTIONS -- Remarks on Indeterminism in Physics (1932) -- A Note on the Concept of Relative Truth (1964) -- On the so-called "Relative Truth" (1963) -- On Abstraction and Concretization (1960) -- PHILOSOPHY OF MIND AND PHILOSOPHY OF PSYCHOLOGY -- On the Nature of Mental Phenomena (1933) -- On the Debate about Imaginative Ideas (1932) -- On the Subjective and Objective Clarity in Thought and Word (1959) -- References -- Original Sources -- Appendix: Wiegner's Conception of Holistic Empiricism.