Every individual event, qua individual, is unique. THought renders events non-unique through classification and generalization. Historical explanation demands understanding causal connections, in turn requiring the use of generalizations. History is a consumer of established laws which introduce a locus of non-uniqueness into history. Also, history is a producer of limited generalizations, covering temporally confined structual patterns which constitute the locus of uniqueness in history. It is the temporal limitation of these patterns, and not the chronological description of facts, which gives history its character of uniqueness