In the 18th century James Burnett, Lord Monboddo analyzed numerous languages and deduced logical elements of the evolution of human languages. His thinking was interleaved with his precursive concepts of biological evolution. Some of his early concepts have been validated and are considered correct today. In his "The Sanscrit Language" (1786), Sir William Jones proposed that Sanskrit and Persian had resemblances to Classical Greek, Latin, Gothic, and Celtic languages. From this idea sprung the field of comparative linguistics and historical linguistics. Through the 19th century, European linguistics centered on the comparative history of the Indo-European languages, with a concern for finding their common roots and tracing their development.