Sinistrisme is a neologism invented by political scientistAlbert Thibaudet in Les idées politiques de la France to explain the evolution and recombination of party systems without substantial changes occurring to party ideology. Thibaudet saw that, over time, issues that previously had not been politicised would emerge, drawing public concern and stimulating a demand for political action. A new political movement would form to champion the new concerns, and this would send repercussions throughout the existing political system. The old party of the left would be split, with some accepting the new issues as legitimate, agreeing to cooperate with the newcomers and adapting their ideology accordingly. Others on the existing left would double down on their existing ideas, refusing change: without having changed their ideas, they would end up pushed de facto one space to the right, and end up as the new centre. Meanwhile, the old party of the centre would be pushed to the centre-right, and so on. As for the very far right, over time the issues of social conservation that motivated them would gradually lose their appeal, and as old issues died off space would be freed up for the old right to become the new far right. France provided the quintessential example. The socially-conservative Liberal Monarchists had been the centre-left of the 1820s, but were pushed to become the new centre by the emergence of socially-conservative republicans in the 1830s. These were pushed to the centre by the emergence of the Radicals in the 1870s; these were pushed to the centre by the emergence in the 1900s of the Radical-Socialists, who were pushed towards the centre by the growth of the socialist French Section of the Workers' International in the 1920s, who were in turn pushed towards the centre by the emergence in the 1950s of the French Communist Party. This process thus explained, to Thibaudet, the tendency of social-conservatives, particularly in France, to disavow the label droite, long associated in French history with monarchism, in favour of left. The emergence of new rivals to their left meant that a political bloc suddenly found itself shifted one space to the right, without considering itself to be a party of the right: thus, political groups in France usually used labels that to an outsider would seem to belong one space to the left:
Radical deputies who had once belonged, unambiguously, to the Radical political family were forced to decide whether or not to join the new Radical-Socialist and Radical Republican Party when this was created in 1901. Those who did not, such as the historic Radical leader Georges Clemenceau, were thus pushed into the centre-right though still considered themselves men of the left. As a result, the non-Radical-Socialist Radicals continued to call their parliamentary party the "Radical Left", though they were now a party of the centre-right almost indistinguishable from the Liberals to their immediate right.
Liberal deputies with socially-conservative views but who accepted economic laissez-faire, parliamentary sovereignty and constitutionalism, were in 1900 situated on the centre-left. As a result, they labelled their parliamentary group the "Republican Left", even when, twenty years later, they were situated firmly on the centre-right of most issues. After the Second World War this terminology persisted: the group that gathered up miscellaneous Radicals and Liberals situated between the Socialists and the Christian-Democrats termed themselves the Rally of Left Republicans.
Catholics and conservatives who accepted the legality of the Republican regime could be found in two groups by 1900. The first, ideologically conservative but tactically accepting the existence of the Third Republic, labelled themselves the "Constitutional" or "Republican Right", whereas those who had a more sincere acceptance of the republican constitution formed, between 1899 and 1901, a party labelled "Liberal Action". Thus the
Monarchists who were elected to parliament under the Third Republic at first proudly displayed that label. Over time, however, it became politically unacceptable to do so, and they shifted their terminology. Thus by the time Thibaudet was writing in 1931, the monarchists on the far-right of parliament labelled themselves "Conservatives", "Independents", or "National Republicans" —labels which to an outsider might seem more logical belonging on the centre-right.
This phenomenon was still at play well into the 20th-century. Historian René Rémond observed that after 1924 the term "right wing" vanished from the glossary of mainstream politics in France, such that "at the 1974 presidential election, only one candidate declared himself as belonging to the right: Jean-Marie Le Pen; in 1981, there was none." Conservative was a synonym of "right wing" often used under the Third Republic, in particular by the Bloc national Chamber. Independents, used in the 1920s for deputies close to the Action française royalist movement, was later used by less reactionary politicians.
