This thesis examines why revolutionary left‑wing parties ceased to pursue the overthrow of capitalism and instead worked for reform within it. A central point of departure is Swedish scholarship on the Social Democratic Party’s reformist development, particularly explanations emphasising adaptation, e.g. to compromise‑oriented parliamentary politics. Building on this research, the thesis develops the adaptation concept by integrating social practice theory and by formulating the complementary concepts of practice change, subversive practice change, and the bridge linking everyday action to the revolutionary goal. The study examines the Communist Party of Sweden (Sveriges Kommunistiska Parti, SKP) in 1943–1953, when it adopted the ‘peaceful road to socialism’ and gained unprecedented influence in parliamentary and municipal politics as well as in the trade unions. Drawing on central party archives, municipal records, and a complete survey of SKP parliamentary motions, as well as selected regional and local cases, the analysis centres on concrete action within these three practices, including at grassroots level. The study also includes several quantitative examinations, including analyses of internal membership statistics.

The findings show, first, that the SKP did not pursue a ‘people’s democratic’ coup d’état; no subversive practice change was attempted vis‑à‑vis the military and police, and the Swedish ‘peaceful road’ was demilitarised. Second, parliamentary and municipal work was largely adaptive: bread‑and‑butter issues dominated, and the party adjusted itself to consensus‑oriented practice. The party’s actions rarely functioned as a bridge because links to the socialist aim were seldom articulated. Third, trade‑union activity was only modestly practice‑changing, mainly challenging the unions’ Social Democratic orientation where the SKP held decisive influence; otherwise, it adapted to reformist practice. In a few strongholds, union work could operate as a bridge by channelling political and material support to the party.

Organisationally, the SKP pursued and partly succeeded in creating a mass party between 1944 and 1948, which can be analysed as a bridge because increased support promoted the ‘peaceful road’. However, this membership expansion was reversed after 1948 amid the Cold War and tighter membership terms, resulting in a drastic decline. The party’s organisational structure increasingly adapted to parliamentary, municipal, and trade‑union practices, e.g. through geographical segmentation, representative forms, and workplace organisations aligned with trade‑union practice. Organisational security measures were primarily aimed at safeguarding the party’s survival and protecting its relations with fraternal parties, rather than enabling subversive practice change.

The thesis provides a method for identifying adaptation and change within practices and introduces the bridge as a way to analyse how everyday actions may, or may not, connect to long‑term socialist goals. It argues that accumulated adaptation generates path dependency that constrains revolutionary capacity, that the absence of practice change reinforces this path, and that temporal and spatial displacement of the revolutionary goal (towards a future moment and the socialist world) helps explain reformist development without complete ideological renunciation. In conclusion, the SKP was characterised by a specific contradiction between social reform and revolution.