The basic natural philosophical questions, which led in the 14th century to the transformation of cosmology, are thoroughly analysed and commented upon with the aid of the Quaestiones of Franciscus de Marchia (d. after 1344), edited here for the first time, and in the light of Aristotelian and Medieval debate. In his precise critique of Aristotle Marchia proved himself to be a precursor of several essential turning point in the development of modern cosmology.