Social democracy was theorized as a bourgeois instrument continuous with fascism.

Evidence

These uncertainties about how fascism should be defined were accompanied by equal uncertainty about its stability and historical prospects. It was still widely believed by communist leaders that the ruling class might decide that the fascist option was too costly, and switch to a social-democratic alternative. The notion that social-democracy was the “left wing of the bourgeoisie” had been generally accepted, for example, by Italian communists since Zinoviev first put it forward in 1922 (by 1924 this had become “the left wing of fascism”). Moreover, it was true that the fascists had not entirely suppressed bourgeois political institutions; indeed, even communist members still sat in the fascist-dominated parliament. — Antonio Gramsci, Selections from the Prison Notebooks, 32

Categorization

• XREF: This Zinoviev formula ‘social democracy as left wing of fascism’ carries into later critical-theory readings of the Third International’s fascism analysis, and prefigures the Frankfurt School’s collapse of liberal into fascist forms.
• DEFINE: Establishes the Comintern’s stage-theory of bourgeois rule where liberal and fascist forms are interchangeable instruments of capital.