In this paper I reconstruct the central concept of the young Lukács's and Mannheim's sociology of knowledge, as they present it in their writings in the early decades of the twentieth century. I argue that this concept, namely Weltanschauung, is used to refer to some conceptually unstructured totality of feelings, which they take to be a condition of possibility of intellectual production, and this understanding is contrasted to an alternative construal of the term that presents it as logically structured, quasi-theoretical background knowledge. This concept has Kantian reminiscences: it is a condition of possibility of intellectual production in general. The young Mannheim and Lukács rely on "Weltanschauung' so understood as a phenomenon mediating between the facts of society and individual intellectual production and reception: it is seen as being conditioned by sociological facts and therefore as a historical and sociological category through which, and therefore indirectly, society enters into intellectual production.