This chapter applies the hylomorphic framework to the second general type of human act that Aquinas countenances, namely, mental human acts. In keeping with the general hylomorphic account, it argues that a mental human act is a composite of a volitional act of use and a mental commanded act. There are various mental powers that we can exercise at will, Aquinas thinks, including memory and the intellect. Aquinas’s most detailed account of a mental act performed at will concerns the act of “reminiscing,” by which Aquinas understands the deliberate attempt to retrieve a piece of information that has fallen from memory. The chapter argues that, in this human act, the component of use and the commanded component, which is an exercise of the power of memory, are both immanent. However, like the components of the bodily human act, they differ in their temporal unfolding. Use is intrinsically instantaneous, whereas the act of memory that it causes is temporally extended. The last section of this chapter considers Aquinas’s view that mental agency can be impeded by obstacles internal to the agent, such as mental illness.