Accident

An accident is that which is apt to exist in another as in a subject of inherence (cui competit esse in alio tanquam in subjecto inhaesionis). Unlike substance, which exists in itself, an accident possesses no autonomous existence: it exists in a substance whose modes or determinations it specifies without constituting its essence.

More specifically

The distinction between substance and accident is one of the most fundamental in classical metaphysics. A substance is that which exists in itself; an accident is that which exists in another. Thus, the color of an object, its size, shape, temperature, location, or certain of its dispositions are accidents: they are real, but only as determinations of a substance that serves as their subject.

An accident is not necessarily something secondary or insignificant. Rather, it is that through which a substance appears under a particular mode. Two beings may share the same essential nature while differing accidentally. A human being may be tall or short, young or old, learned or ignorant: such characteristics modify a person’s state without altering his or her humanity itself.

Aristotle distinguishes several categories of accidents: quantity, quality, relation, place, time, position, possession, action, and passion. This classification seeks to describe the various ways in which a substance may be determined without ceasing to be what it is. Accident therefore belongs to the order of becoming and the diversity of manifestations, whereas substance refers to the permanence of being.

In Scholastic philosophy, accidents are genuine realities, though dependent ones. They are not merely mental constructions; they possess a certain reality, even though they cannot exist apart from their subject. This ontological dependence explains why an accidental change does not necessarily entail a substantial change. When a tree grows or loses its leaves, it remains the same tree; when a person learns a language or changes clothing, he remains the same person.

The distinction between substance and accident also plays a major role in theology. In the doctrine of the Eucharist, for example, transubstantiation signifies the change of the substance of bread and wine into the Body and Blood of Christ, while the accidents—appearance, taste, color, weight, and other sensible qualities—remain unchanged. This doctrine presupposes precisely the metaphysical distinction between what a thing is and how it appears.

More broadly, the notion of accident reminds us that the visible appearance of a being does not exhaust its deeper reality. Accidental determinations are real, but they point beyond themselves to a more fundamental reality upon which they depend. Metaphysics thus seeks to move beyond the order of accidents in order to attain substance, and beyond particular substances to the universal principles of being itself.

More specifically

Further reading