The aim of this paper is to take Galileo's mathematization of nature as a springboard for contrasting the time-honoured empiricist conception of phenomena, exemplified by Pierre Duhem's analysis in To Save the Phenomena (1908), with Immanuel Kant's. Hence the purpose of this paper is twofold. I) On the philosophical side, I want to draw attention to Kant's more robust conception of phenomena compared to the one we have inherited from Duhem and contemporary empiricism. II) On the historical side, I want to show what particular aspects of Galileo's mathematization of nature find a counterpart in Kant's conception of phenomena.