Before refraining: Concepts for agency

A structure is described that can serve as a foundation for a semantics for a modal agentive construction such as “a sees to it that Q” ([a stit: Q]). The primitives are Tree,=,Instant, Agent, choice>. Eleven simple postulates governing this structure are set forth and motivated. Tree and = encode a picture of branching time consisting of “moments” gathered into maximal chains called “histories.” Instant imposes a time-like ordering. Agent consists of agents, and choice assigns to each agent and each moment in Tree a set of “possible choices”, where each possible choice is a set of histories. All of these ingredients are referred to in the semantics suggested for [a stit: Q]. The most complex part of the discussion is the motivation for the definition of what it means for a typically non-terminating chain of moments jointly to witness the truth of [a stit: Q] at a moment.