This article investigates how framing processes lead to polarization in the public debate on a large infrastructure project. Drawing on an analysis of newspaper articles about the Oosterweelconnection in Antwerp (Belgium), it concludes that framing through imaginative appeals and framing through evidence mutually reinforce each other in a spiralling pattern. When evidence backs up appeals to the imagination, such as when facts back up metaphors, these appeals are endowed with authority and hence legitimacy. While this strengthens appeals that have been ”proven” to be true, it also makes actors backing these appeals increasingly frustrated with other parties that still refuse to accept them. Because of their frustration, the former are spurred to launch new imaginative appeals conveying their anger and to seek new evidence to substantiate these new appeals. Over time, as parties in a conflict grapple with evidence and imagination, their tolerance for ambiguity decreases and the debate polarizes.