 In mathematics, it is generally possible to frame absolute demonstrations, because the premises both supply the cause and are better known than their conclusions. In the natural sciences, however, and even in metaphysics, this ideal situation is generally not achievable. Here we begin with the accidental sensible features of things, and so extensive use must be made of the demonstration of existence (EpiPhys 1.105 {9}; Sylla 1979; Cerami 2014). Ibn Sīnā, whose views are often the target of Ibn Rushd’s logic, had denied that these count as a demonstration at all, on the grounds that they establish no substantial connection between the posterior cause and the prior effect. Ibn Rushd rejects this view (LongPostAn I.95 {349}), but admits that the demonstration of existence is less reliable than the other demonstrations. Certainty comes in degrees, and the differentiation in certainty between these demonstrations is one of the reasons why some sciences are superior to others (ParaPostAn §88–9).