(AP) What "is" is

The "is" of identity:

A cat is a mammal.

The "is" of simple predication:

The cat is on the mat.

The "is" of (Clintonian) existential predication:

There is no affair.

The "is" of moral judgment:

War is evil.

The "is" of artistic identification:

That upside-down tree is a work of art.

See also Sherri Irvin's critical commentary on Danto's "is of artistic identification/constitution."