An attribute of a substance that does not belong directly to its nature. 

Contingent Accident.— An accident in a substance that can come to exist and cease to exist without necessarily destroying the substance or can be found in some substances of the same kind but not in others of that kind. E.g., a person’s height, weight, or nationality. The word “accident” used without a modifier typically denotes a contingent accident. 

Necessary Accident (also called Physical Property).— An accident in a substance that, although it does not belong directly to the nature of the substance, necessarily follows from the nature. E.g., the human capacity for humor, which necessarily follows from having an intellect and, hence, the power to understand.