Sixth year LPS graduate student Michael Ernst presented his recent research at two international workshops on the philosophy of mathematics in Europe in late June and early July. His paper describes a new paradox in the important foundational area of mathematics known as category theory. This paradox suggests that it is not possible to formalize category theory in a way that at some mathematicians and philosophers have argued would be desirable. The first event was hosted by the SPHERE working group at the University of Paris, 7, on June 25; the second was a conference titled "What can Category Theory do for Philosophy?", hosted by the University of Kent from July 9 to the 11th.