  In the 1920s, American jurisprudence came under the influence of another version of the critical view of ideology and law. The school of legal realism abandoned Marx’s specifically historical materialist explanation, but took up the idea that social forces outside the law are central in determining what the law is (see Cohen 1935, 818–21). Realists opposed traditional ‘formalist’ accounts of adjudication, where judges are understood to rely on uniquely and distinctively legal materials in rendering their judgments. Instead, the realists contended that law is inherently indeterminate, and thus judicial decisions must be explained by factors outside the law. Ideology emerges as one kind of realist explanation, where judicial decisions are the effect of political ideas, be they of the judge, the legal profession more generally, societal elites, or majority public opinion. The realists aligned their critique of law with a progressive politics. The inevitable influence of factors external to the law meant that social and political changes augured by the emerging welfare state were no threat to the purity of law. Indeed, the expanding regulative power of the administrative state would make it more likely that the influences on the law were now those of popular sovereignty and social justice, rather than the more nefarious influences of the past.