Four experiments investigate a novel finding in the area of symbolic magnitude comparisons: Congruity effects may occur with subsets of objects.  Such multiple congruity effects appear to signal the creation of size-ordered categories.  Experiment 1 observed separate congruity effects for large and small pairs despite the intermingling of pairs within a session.  Experiment 2 determined whether this result was an artifact of the items used.  Experiments 3 and 4 examined whether linear separability on a dimension of size or some other correlated dimension was a prerequisite for multiple size-ordered categorization.  The results of these experiments suggest that congruity effects are properly regarded as indicating the presence of an organized structure or category.  Thus, to the extent that congruity effects typify magnitude comparisons, the processing of relational information appears to implicate categorization.