If there is only one possible course of future events, then it becomes hard to argue that I am responsible for what I do. I will, no doubt, act according to my nature, but I do not have a choice between possibilities, in the sense that I could have done otherwise than what I did.
I therefore postulate many possible courses of events in the future, and a single course of events in the past. Courses of events therefore branch at the present (cf. Lucas (1989)). A total course of events may be called a possible world. (Note: The term 'possible world' has a different meaning in my discussion of time under Philosophy.) As events take a certain course, many possible worlds disappear. (I take possible worlds to be abstract rather than concrete.) The model assumes that conscious beings can, to some extent, make free choices between different possible worlds. There is then obviously room for responsibility.
God has created all the possibilities there are, so he knows all possible worlds. For particular events, we can say that a future event is necessary at a certain time if and only if it occurs in the future in all possible worlds existing at that time. In this way there can be future events which are certain in spite of some freedom of choice for agents. (A future event is impossible if and only if it occurs in no possible world.)
Similarly, a future event is possible at a certain time if and only if it occurs in the future in some possible worlds existing at that time. There is no knowledge as to how a free choice will be made.
J. R. Lucas (1989) The Future, Blackwell,
Last updated: 04 January 2005