Difference is a key concept of philosophy, denoting the process or set of properties by which one entity is distinguished from another within a relational field or a given conceptual system. In the Western philosophical system, difference is traditionally viewed as being opposed to identity, following the Principles of Leibniz, and in particular, his Law of the identity of indiscernibles. In structuralist and poststructuralist accounts, however, difference is understood to be constitutive of both meaning and identity. In other words, because identity (particularly, personal identity) is viewed in non-essentialist terms as a construct, and because constructs only produce meaning through the interplay of differences (see below), it is the case that for both structuralism and poststructuralism, identity cannot be said to exist without difference.