Abstract 
Branching space-time
is a simple blend of relativity and indeterminism. Postulates and definitions rigorously describe the
causal order
relation between possible point events. The key postulate is a version of
everything has a causal origin
; key defined terms include
history
and
choice point
. Some elementary but helpful facts are proved. Application is made to the status of causal contemporaries of indeterministic events, to how
splitting
of histories happens, to indeterminism without choice, and to Einstein-Podolsky-Rosen distant correlations.