Semaun joined SI in 1914 and also ISDV in 1915, leading him to hold dual party membership. Semaun militantly advocated the communist ideas and pushed for the leftist turn of SI, competing with the more moderate position taken by the central SI leaders such as Tjokroaminoto.
Semaun became a member of both SI in 1914 and ISDV in 1915, which resulted in his dual party affiliation. Semaun energetically advocated for communist principles and pushed for the leftist direction within SI, contrasting with the more moderate views held by central SI leaders such as Tjokroaminoto.