Hugh of Novocastro, Landolfo Caracciolo, John Baconthorpe, and some other medieval authors argued that there are real contradictions in nature. The background of this early fourteenth-century theory was the Aristotelian question of how to determine the instant of change between p and ~p. The argument was that these are simultaneously true at the temporal instant of change if it is an instant of changing. The author’s aim is to discuss the background of this view in Henry of Ghent’s theory of (...) instantaneous change from potentiality to actuality at that very instant. (shrink)