  The interaction axioms raise questions concerning asymmetries between the past and the future. A standard intuition is that the past is fixed, while the future is still open. The first interaction axiom \((A\rightarrow GPA)\) conforms to this intuition in reporting that what is the case \((A)\), will at all future times, be in the past \((GPA)\). However \(A\rightarrow HFA\) may appear to have unacceptably deterministic overtones, for it claims, apparently, that what is true now \((A)\) has always been such that it will occur in the future \((HFA)\). However, possible world semantics for temporal logic reveals that this worry results from a simple confusion, and that the two interaction axioms are equally acceptable.