A fundamental fact is “pure” just in case it has no grounded entities—ex. Tokyo, President Biden, the River Nile, {Socrates}, etc.—among its constituents. Purity is the thesis that every fundamental fact is pure. I argue that Purity is false. My argument begins with a familiar conditional: if Purity is true, then there are no fundamental “grounding facts” or facts about what grounds what. This conditional is accepted by virtually all of Purity’s defenders. However, I argue that it is also the (...) first step toward Purity’s undoing. For, if every grounding fact has a ground, then some grounded entities have “groundmates” or distinct grounded entities that share their full grounds. But, if there are groundmates, then Purity is false. So Purity leads to a contradiction. Therefore, it is false. I close by noting that my argument against Purity also gives us a powerful reason to think that some grounding facts are fundamental. (shrink)