That is, y will occur only when x occurs. For example, the launching of American ICBMs involves a complex set of simultaneous procedures to be carried out by more than one person. There is a special type of sufficient cause that I will call a trigger. This is a class of causes x that operates within a system of conditions highly favorable for producing y, such that any member of the class x could have produced y and would not have been a cause without these conditions. The trigger is often called the proximate or immediate cause.
Specific triggers are therefore random causes.
They are not of intrinsic interest except as a class of events. What is of interest are the causes and conditions that must cooccur for triggers to be successful and the specific, sufficient causes that make certain that some random trigger will spring y. Then there are conditions z of y. Conditions, in my sense, retard or enhance the operations of a cause. Setting a match to kindling is a sufficient cause of fire. World opinion similarly could inhibit or aggravate violence depending on whether it was strongly opposed or favorable.