Wikipedia
Partiinost' is a transliteration of a Russian term from Marxism-Leninism. It can be variously translated as party-mindedness, partisanship, or party spirit. The term can refer to both a philosophical position concerning the sociology of knowledge and an official doctrine of public intellectual life in the Soviet Union.
The term was coined by Vladimir Lenin in 1895, responding to Peter Struve, to counter what he considered to be the futility of objectivity in political economic analysis. Class interests and material conditions of existence determine ideology, and thus, in a Marxist-Leninist view, true objectivity (in terms of non-partisanship) is not possible in a society of antagonistic classes. Marxists, in Lenin's view, should openly acknowledge their partisanship on the side of proletarian revolution. Bourgeois emphasis on the normative goal of objectivity is thus considered to be delusional. In this sense, partiinost' is a universal and inevitable element of political and ideological life, but its presence is not always acknowledged, or is often flatly denied, by the ruling class.
Descriptively, partiinost' was not a novel concept, and had been described in different words by Thrasymachus, Xenophanes, and Karl Marx. However, Lenin's term has a normative element that was not present in prior descriptions of the phenomenon. In other words, Lenin insisted that partiinost' should be publicly expressed whenever possible.
A clear expression of partiinost' can be found in its entry in the Great Soviet Encyclopedia:
The Communist Party consistently upholds the principle of partiinost'. Defending and substantiating the goals and tasks of the working class and the policies of the Communist Party, Marxist-Leninist theory mercilessly criticizes the exploiters' system, its politics, and its ideology. ... By contrast, the bourgeoisie, whose interests conflict with those of the majority, is forced to hide its self-seeking aspirations, to pretend that its economic and political aims are those of society as a whole, and to wrap itself in the toga of non-partisanship
Partiinost' is also used by Lenin in Materialism and Empirio-criticism to refer to the concept of philosophical factionalism, which he defined broadly as the struggle between idealists and materialists. The term is also commonly used in modern Russian to describe political affiliations.