Accidental Properties

The distinction between essential versus accidental properties has been characterized in various ways, but it is often understood in modal terms: an essential property of an object is a property that it must have, while an accidental property of an object is one that it happens to have but that it could lack. Let’s call this the basic modal characterization, where a modal characterization of a notion is one that explains the notion in terms of necessity/possibility. In the characterization just given of the distinction between essential and accidental properties, the use of the word “must” reflects the fact that necessity is invoked, while the use of the word “could” reflects that possibility is invoked. The notions of necessity and possibility are interdefinable: to say that something is necessary is to say that its negation is not possible; to say that something is possible is to say that its negation is not necessary; to say that an object must have a certain property is to say that it could not lack it; and to say that an object could have a certain property is to say that it is not the case that it must lack it.

Read the rest here:  https://plato.stanford.edu/entries/essential-accidental/

According to the AI

In philosophy, accidental properties are properties an object has contingently, not essentially.

An accidental property is one that a thing can gain or lose without ceasing to be what it is. Example:
– A chair being red.
– Socrates being bald.
– This book lying on the table.

If the property changes, the object remains the same kind of thing.

This contrasts with essential properties, which an object must have to be what it is. Example:
– A triangle having three sides.
– A human being rational (in the Aristotelian sense).

The distinction goes back to Aristotle’s Categories and Metaphysics. Accidental properties depend on circumstances, relations, or states, not on the object’s defining nature.

In short: accidental properties describe how something happens to be, not what it is.

Wikipedia

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. 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. 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 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.

Read the rest here: https://en.wikipedia.org/wiki/Accident_(philosophy)