This article explores Marx and Engels' infamous theory ideology, which I argue is best understood as a critique of ideation. The piece explores what the pair did and did not say about ideology and similar concepts, focusing on six key terms: alienation, mystification, commodity fetishism, social consciousness, ideology, and false consciousness. I read across the Marxian corpus, from The 1844 Manuscripts and The German Ideology to the three volumes of Capital and Engels' late writings. Along the way, the article advances two fundamental claims: 1) Marx and Engels' views on ideation are more multifaceted than is often assumed; 2) the two authors provide a broad lexicon for the critique of ideation, one that allows for the construction of a dynamic portrait of consciousness within the social totality of capitalism. Ultimately, the account is not designed as a master theory meant to replace all other forms of analysis, Marxist or not. As a result, the critique of ideation operates in tandem with their other intellectual contributions (to economics, history, and the like). Further, it is compatible with perspectives from aesthetics, the natural sciences, and a range of other disciplines. Even so, it offers potent resources for analyzing forms of thought under capitalism, supplementing larger discussions within Marxism and without.