Example
My house alarm system just sounded (A).
Both an earthquake (E) and a burglary (B) could set it off.
John will probably hear the alarm; if so he’ll call (J).
But sometimes John calls even when the alarm is silent
Mary might hear the alarm and call too (M), but not as reliably
We could be assured a complete and consistent model by fully specifying the joint distribution:
Prob(A, E, B, J, M)
Prob(A, E, B, J, ~M)
etc.