Understanding the “intentionality” of mental phenomena is widely regarded as a key problem in philosophy of mind. Franz Brentano (along with his students, especially Edmund Husserl) is widely credited with bringing intentionality to philosophers’ attention. In early treatment by the Brentano school, intentionality is at least nominally understood as executed, brought about, or achieved in mental acts. And in the early 20th century, historians of psychology regarded this “act conception” of intentionality as integral for understanding the phenomenon. Yet the secondary (...) literature on Brentano and Husserl provides no clarification of mental acts as acts, and in contemporary philosophy, we have no workable account of what it could mean for intentionality to arise through mental acts. The main difficulty is that “act” is widely regarded as synonymous with “volitional personal action.” Since we as human agents certainly do not willfully bring about much of our own mental life, and since (on the standard analyses) all such volition presupposes intentionality, it is a mystery to work out what the act conception of intentionality could have amounted to. This dissertation is a systematic explication of the historical act concept of intentionality. Part I examines Brentano. I show that his early work on Aristotle’s psychology provides resources to think coherently about many mental phenomena as acts, even if they are not personal actions. However, I also show that Brentano’s mature psychology is not Aristotelian, at least insofar as it does not (and cannot) deploy an Aristotelian conception of mental acts. Part II examines Husserl. I show that Husserl’s mature transcendental phenomenology works with a robust and many-layered conception of mental acts, and that understanding intentionality as active is essential to the phenomenological viewpoint. Moreover, I argue that Husserl’s conception of mental acts can be viewed as a transcendentalized, neo-Aristotelian view. The results will be of special interest to historians of philosophy, but also have a much broader significance. Husserl’s view provides us with a model of what can be called an “internalist enactivism.” Any view along these lines represents a novel position that has not been articulated (or even considered) in contemporary debates. (shrink)