“A feature or property of a substance (e.g., an organism or artifact) without which the substance could still exist. According to a common essentialist view of persons, Socrates’ size, color, and integrity are among his accidents, while his humanity is not. For Descartes, thinking is the essence of the soul, while any particular thought a soul entertains is an accident. According to a common theology, God has no accidents, since all truths about him flow by necessity of his nature. . . . Issues about accidents have become peripheral in this century because of the decline of traditional concerns about substance. But the more general questions about necessity and contingency are very much alive.”
– Steven J. Wagner, The Cambridge Dictionary of Philosophy, 2nd ed., 5.