The following statement by Suppes [Suppes 1994] provides a good excuse for beginning with a very simple example of introspective free will.
There are, it seems to me, two central principles that should govern our account of free will. The first is that small causes can produce large effects. The second is that random phenomena are maximally complex, and it is complexity that is phenomenologically in many human actions that are not constrained but satisfy ordinary human notions of being free actions.[my emphasis]
I don't agree that complexity is essentially involved so here's a minimal example that expresses, ``I can, but I won't''.
Because the agent is reasoning about its own actions, as is common in situation calculus formalization, the agent is not explicitly represented. Making the agent explicit offers no difficulties.
If an action a is possible in a situation s, then the situation Result(a,s) that results from performing the action is achievable.
If a situation Result(a,s) is achievable and every other situation that is achievable is less good, then the action a should be done.
Here means ``not so good as''.
Actions leading to situations inferior to what can be achieved won't be done.
This is reasonably close to formalizing ``It can, but it won't'' except for not taking into account the distinction between ``but'' and ``and''. As truth functions, ``but'' and ``and'' are equivalent. Uttering ``p but q'' is a different speech act from uttering ``p and q'', but this article is not the place to discuss the difference.