The context of 18th century thought is of particular relevance in the Western World in regard to the change of traditional mimetic to non-mimetic poetics: this is the case with the Swiss poetical theories of possible worlds and with the romantic, post-romantic and modernist sequences from about the 1740's/1750's until the 1930's/1940's. Emphasis ill be placed, however, on the influence of Leibniz' thinking on language in the creation of a valid alternative to mimetic theories through the concept of possible worlds.