An accident (Greek συμβεβηκός), in metaphysics and philosophy, is a property that the entity or substance has contingently, without which the substance can still retain its identity. An accident does not affect its essence, according to many philosophers.[1] It does not mean an "accident" as used in common speech, a chance incident, normally harmful. Examples of accidents are color, taste, movement, and stagnation.[2] Accident is contrasted with essence: a designation for the property or set of properties that make an entity or substance what it fundamentally is, and which it has by necessity, and without which it loses its identity.
Aristotle made a distinction between the essential and accidental properties of a thing. Thomas Aquinas and other Catholic theologians have employed the Aristotelian concepts of substance and accident in articulating the theology of the Eucharist, particularly the transubstantiation of bread and wine into body and blood. In this example, the bread and wine are considered accidents, since at transubstantiation, they become incidental to the essential substance of body and blood.
In modern philosophy, an accident (or accidental property) is the union of two concepts: property and contingency. Non-essentialism argues that every property is an accident. Modal necessitarianism argues that all properties are essential and no property is an accident.