Claim: Viktor Chernov was an early joiner of the Socialist-Revolutionary Party, who published the book "Philosophical and Sociological Studies", for which he was criticized by Lenin.
Evidence: He joined the Socialist-Revolutionary Party upon its founding in 1901 and became the editor of its newspaper Revolutionary Russia. In 1907, he published Philosophical and Sociological Studies in which he espoused the viewpoint of Richard Avenarius. As such, he was one of the Russian Machists criticised by Lenin in Materialism and Empirio-criticism (1909).