 A life L is a sequence of acts over time, or, in the terminology of this article, an act-set over time, such that this act-set is not contained in some other act-set that an agent S can perform over time. Hence, a life is identical to the possibilist’s notion of a maximal act-set. A life L is securable for S at time t if at \(t\) \(S\) can immediately perform the first moment of x, x is in L, and if x were to occur, then L would occur (Sobel 1976: 199). An obligatory life is determined in part by the set of immediately performable fully specific minimal acts available to the agent. A minimal act is one whose completion cannot be stopped by the agent once it is initiated. As such, all instantaneous acts are minimal acts (if there are any such acts). Moreover, a minimal act is fully specific just in case it is not entailed by two or more minimal acts available to the agent.