Trigger
In its earliest usage, "trigger" refers to a mechanical mechanism, the pulling or pushing of which sets a device into action. This includes the lever that sets off the chain of events that fires a gun, the release mechanisms on a crossbow, or the lever that engages an animal trap.Today "trigger" is also used in a wider sense to refer to a precipitating cause of some event. The "trigger" (noun) is said to "trigger" (verb) the event.
Note that, in this wider sense, "trigger" need not be a necessary condition for the event. To the extent that it is a sufficient condition, this is only relative to some implied background conditions taken as given. (See necessary and sufficient conditions.)
Examples of "triggers":
- If one adds a seed crystal to a supersaturated solution, the crystal will "trigger" the precipitation of the dissolved material.
- In the almost cliche idea of a butterfly flapping its wings and thereby causing a great weather disturbance (see chaos theory), the butterfly can be said to have "triggered" the disturbance.
- An event which causes an allergic reaction or other untoward psychological/physical event is also referred to as a trigger. For example, exposure to cat dander may trigger an asthma attack in an allergic person, and persons with post-traumatic stress disorder may experience extreme distress after being exposed to their personal trigger.
- In computer programming, software may be set up so that certain events (e.g. an insert, an update or a delete of a database) trigger the invocation of particular procedures.