In the case of catenanes containing a stereogenic centre in each ring, ligand permutation (Supplementary section 14.2) reveals four diasteromers (Fig. ) and their enantiomers (eight stereoisomers total), consistent with two covalent and one mechanical stereogenic unit. However, the nature of the mechanical stereochemistry is ambiguous; each structure can be assigned both a mechanical axial or a mechanical topological stereodescriptor, but only one of these is required to fully specify the structure. This analysis suggests that it would be incorrect to describe such catenanes as simultaneously topologically and mechanically axially chiralone of the stereolabels would be redundantbut that it is unclear which description should take priority. This analysis may appear philosophical in nature but has implications for the synthesis of chiral catenanes. If a single diastereomer of such a catenane could be isolated, it could be converted to an axially chiral catenane by selective symmetrization of the in-plane substituents, or a topologically chiral catenane by symmetrization of the out-of-plane substituents (Fig. ). This analysis further highlights that how a stereogenic unit is conceptualized can guide the development of new methodologies.