Plant taxonomy is an empirical science, a science that determines what constitutes a particular taxon (taxonomic grouping, plural: taxa): e.g. "What plants belong to this species?" and "What species belong to this genus?". The definition of the limits of a taxon is called its 'circumscription'. For a particular taxon, if two taxonomists agree exactly on its circumscription, rank and position (i.e. the higher rank in which it is included) then there is only one name which can apply under the "ICN". Where they differ in opinion on any of these issues, one and the same plant may be placed in taxa with different names. As an example, consider Siehe's Glory-of-the-Snow, "Chionodoxa siehei":