Deﬁnitions of art
Deﬁning can take a variety of forms: for instance, pointing to examples, enumerating all the things that fall under the term at issue, or legislating how a term will be used. One particular type of deﬁnition, sometimes called ‘essential’ or ‘real’ deﬁnition, has special power as an analytic tool. A real deﬁnition of something, X say, would identify a set of properties such that each and every X has all the properties that make up the set and only Xs have that set of properties. A real deﬁnition speciﬁes a group of properties each of which is necessary for something’s being an X and which, taken as a group, are also sufﬁcient for something’s being an X. In other words, a deﬁnition of X characterizes what all Xs and only Xs have in common. For instance, a widow is a woman who has lost her husband by death and who has not married again. In this case, there are three necessary conditions that together are sufﬁcient for someone’s being a widow.