Legal fictions are usually defined as consciously false assumptions. This definition is suitable for distinguishing fictions from presumptions, but it conceals some important nuances about the role of fictions in a legal system. For this reason, this paper proposes an alternative definition of legal fictions as discrepancies between different conceptual systems. In doing so, it makes it possible to focus not primarily on external fictions, which consist in a discrepancy between legal terminology and colloquial language, but rather on internal fictions, which consist in a discrepancy between two versions of a legal conceptual system. The juxtaposition of two versions of a legal conceptual system makes it clear that the addition of an internal fiction, as the most trivial form of representation for the result of an analogy, increases the distinctiveness of a system in an expedient way, but at the cost of a significant loss of perspicuity. As long as the internal fiction plays only a marginal role, it can provide a clever and elegant solution. But when it assumes a structural role, it is accompanied by too great a loss of perspicuity, and is therefore an indication that the system could profitably be restructured by explicitly adjusting the meaning of some of its key concepts.