the German linguist Leo Weisgerber. Whorf's principle of linguistic relativity was reformulated as a testable hypothesis by Roger Brown and Eric Lenneberg who conducted experiments designed to find out whether color perception varies between speakers of languages that classified colors differently. As the study of the universal nature of human language and cognition came into focus in the 1960s the idea of linguistic relativity fell out of favor among linguists. From the late 1980s, a new school of linguistic relativity scholars has examined the effects of differences in linguistic categorization on cognition, finding broad support for non-deterministic versions of the hypothesis in experimental contexts. Some effects of linguistic relativity have been shown in several semantic domains, although they are generally weak. Currently, a balanced view of linguistic relativity is espoused by most linguists holding that language influences certain kinds of cognitive processes in non-trivial ways, but that other processes are better seen as arising from connectionist factors. Research is focused on exploring the ways and extent to which language influences thought. Ancient philosophy to the Enlightenment The idea that language and thought are intertwined is ancient. In his dialogue Cratylus, Plato explores the idea that conceptions of reality, such as Heraclitean flux, are embedded in language. But Plato has been read as arguing against sophist thinkers such as Gorgias of Leontini, who held that the physical world cannot be experienced except through language; this made the question of truth dependent on aesthetic preferences or functional consequences. Plato may have held instead that the world consisted of eternal ideas and that language should reflect these ideas as accurately as possible. Nevertheless, Plato's Seventh Letter claims that ultimate truth is inexpressible in words. Following Plato, St. Augustine, for example, held the view that language was merely labels applied to already existing concepts. This view remained prevalent throughout the Middle Ages. Roger Bacon held the opinion that language was but a veil covering up eternal truths, hiding them from human experience. For Immanuel Kant, language was but one of several tools used by humans to experience the world. German Romantic philosophers In the late 18th and early 19th centuries, the idea of the existence of different national characters, or Volksgeister, of different ethnic groups was the moving force behind the German romantics school and the beginning ideologies of ethnic nationalism. Swedish philosopher Emanuel Swedenborg inspired several of the German Romantics. As early as