precipitant

A precipitant is a cause or reason for some event. So if you skip your Biology test on March 17th, your parents might deduce that your enjoyment of the St. Patrick's Day parade was a precipitant of your actions.

See the pre in precipitant? Since pre means "before," you can remember that a precipitant always comes before something else. Precipitant can also mean "hasty" — a precipitant marriage is one where both parties marry too quickly. Not to be confused with percipient, meaning someone with unusual sensitivity and understanding of people and events. A percipient person would never skip his Biology test.