Husserl's Logische Untersuchungen (1900/1901)
In the first edition of the Logical Investigations, still under the influence of Brentano, Husserl describes his position as "descriptive psychology." Husserl analyzes the intentional structures of mental acts and how they are directed at both real and ideal objects. The first volume of the Logical Investigations, the Prolegomena to Pure Logic, begins with a devastating critique of psychologism, i.e., the attempt to subsume the a priori validity of the laws of logic under psychology. Husserl establishes a separate field for research in logic, philosophy, and phenomenology, independently from the empirical sciences.
Read more about this topic: Phenomenology (philosophy)