He joined the Social Democratic Labour Party (Sociaal-Democratische Arbeiderspartij or SDAP) in 1897.
He and his wife became friends with the artist R.N. Roland Holst and his wife, the poetess Henriette Roland Holst, and the poet Herman Gorter, who all lived near their home in Blaricum.
Witsen wrote under a pseudonym in the literary magazine De Nieuwe Gids, which he also supported financially.His circle of friends included the painters George Hendrik Breitner, Isaac Israëls, and Jan Veth and the writers Lodewijk van Deyssel, Albert Verwey, Willem Kloos, and Herman Gorter.
Herman Melville | Woody Herman | Herman's Hermits | Herman Wouk | Herman Hollerith | Edward S. Herman | Herman Daly | Herman Van Rompuy | Herman Dune | Herman Brood | Herman Willem Daendels | Herman Gorter | Herman Finck | Herman Boerhaave | Herman | Herman Wirth | Herman Rarebell | Herman Kahn | Herman Brusselmans | Pee-Wee Herman | Herman Wallace | Herman van Veen | Herman Talmadge | Herman Moore | Herman L. Taylor, Jr. | Herman Kogan | Herman Joseph Justin | Herman I, Duke of Swabia | Herman Heijermans | Herman Haupt |
Other prominent Tachtigers' works first appeared in The New Guide, including the literary critic Lodewijk van Deyssel, and the novelist Herman Gorter, who is probably the most widely read Tachtiger.
The French equivalent, ultra-gauche, has a stronger currency, as it is a more positive term in that language and is used to define a movement that still exists today: a branch of left communism descending from theorists such as Amadeo Bordiga, Otto Rühle, Anton Pannekoek, Herman Gorter and Paul Mattick, and continuing with more recent writers, such as Jacques Camatte and Gilles Dauvé.