Franz Brentano is one of the founding fathers of twentieth century philosophy, celebrated for introducing the concept of intentionality to philosophy as well as making significant contributions to ethics and logic. His work exerted great influence on major philosophers such as Edmund Husserl, but also philosophers travelling in the opposite direction, such Gottlob Frege. He counted Sigmund Freud amongst his students and Freud expressed great admiration for his teacher in several letters.