Phenomenology is a direct reaction to the psychologism and physicalism of Husserl's time. It is one of the representative works in psychologism or intellectualism literature from the 1930s. She is known for her research on psychologism. It drew the adverse notice of Gottlob Frege, who criticized its psychologism. Other forms of psychologism are logical psychologism and mathematical psychologism. The philosopher Robert Sokolowski credited Husserl with providing a convincing critique of psychologism. However, Santayana would reject this approach, which he called "skirt[ing] psychologism," later on in life. Such criticisms did not immediately extirpate what is called "psychologism". Volume One contains seasoned reflections on "pure logic" in which he carefully refutes "psychologism". In psychologism, mathematical objects are mental objects. Heidegger believed that the second volume marked an apparent revival of psychologism, which puzzled him. Psychologism views mathematical proofs as psychological or mental objects. Psychologism was also criticized by Charles Sanders Peirce and Maurice Merleau-Ponty. "It is thought that 'no-p is a not-p'", psychologism does not logically stand.