Activism is defined in this paper as involving local instigations of new series of elements intersecting the actual, generating new collective enunciations, experimentations and investigations, which erode good and common sense and cause structures to swing away from their sedimented identities. By appealing to Spinozism, the paper describes the microphysics of the activist encounter with stable structures and the ways in which activism imposes new regimes of succession of ideas and affective variations in the power of action. Rather than understanding (...) activism as supporting or leading social struggles, the definition of activism pursued here conceives it as an open-ended process and stresses the role of investigation in relation to practices within the social situations to which activism addresses itself. (shrink)