Before the 19th cent., language was studied mainly as a field of philosophy. Among the philosophers interested in language was Wilhelm von Humboldt, who considered language an activity that arises spontaneously from the human spirit; thus, he felt, languages are different just as the characteristics of individuals are different. In 1786 the English scholar Sir William Jones suggested the possible affinity of Sanskrit and Persian with Greek and Latin, for the first time bringing to light genetic relations between languages. With Jones's revelation the school of comparative historical linguistics began. Through the comparison of language structures, such 19th-century European linguists as Jakob Grimm, Rasmus Rask, Karl Brugmann, and Antoine Meillet, as well as the American William Dwight Whitney, did much to establish the existence of the Indo-European family of languages.