A property is essential for

an object if the object must have the property to

exist and be the kind of thing that it is. A property

is accidental if the object has the property, but

doesn’t have to have it to exist or be the kind of

thing that it is.

Suppose Fred has short hair. That is an accidental

property of his. He would still be Fred,

and still be a human being, if he let his hair grow

long or shaved it off completely. An essential

property is one that a thing has to have to be the

thing that it is, or to be the kind of thing it fundamentally

is. As a human being, Fred wouldn’t

exist unless he had a human body, so having a

human body is an essential property of his.

Statements about which properties are essential

tend to be controversial. A dualist might disagree

about our last example, arguing that Fred is

fundamentally a mind that might exist without

any body at all, so having a body isn’t one of his

essential properties. Someone who has been reading

Kafka’s Metamorphoses might argue that Fred could turn into a cockroach, so having a human

body isn’t one of his essential properties. Some

philosophers argue that the metaphysical idea

that underlies the accidental–essential distinction

is wrong. Things belong to many kinds, which

are more or less important for various classificatory

purposes, but there is no kind that is more

fundamental than all others apart from such purposes.

Quine, a leading skeptic, gives the example

of a bicyclist: If Fred is a bicyclist, is he necessarily

two-legged?