Another definition sees language as a formal system of signs governed by grammatical rules of combination to communicate meaning. This definition stresses the fact that human languages can be described as closed structural systems consisting of rules that relate particular signs to particular meanings. This structuralist view of language was first introduced by Ferdinand de Saussure. Some proponents of this view of language, such as Noam Chomsky, define language as a particular set of sentences that can be generated from a particular set of rules.[6] The structuralist viewpoint is commonly used in formal logic, semiotics, and in formal and structural theories of grammar, the most commonly used theoretical frameworks in linguistic description. In the philosophy of language these views are associated with philosophers such as Bertrand Russell, early Wittgenstein, Alfred Tarski and Gottlob Frege.