The current chapter addresses the seminal work that introduces the framework for Brentano's dynamic psychology of psychic [psychischen] or mental acts. A close examination of Brentano's PES will reveal a sophisticated form of empiricism articulated as the basis for his philosophy of mind. In the first Book of the PES Brentano outlines a philosophical and methodological framework to support the above "act' psychology. Brentano's theoretical framework for understanding the mental can ultimately be viewed as an epistemologically clarified analysis of experience centered on a new doctrine of mental reference.