The Questiones libri Porphirii is a commentary on Porphyry's Isagoge by the fourteenth-century logician Thomas Manlevelt. It is edited here in full. Not much is known of Thomas Manlevelt, but his work is remarkable enough. Following in the footsteps of William of Ockham, Manlevelt stresses the individual nature of all things existing in the outside world. He radically challenges our conceptional framework. He applies Ockham's razor in a ruthless manner to do away with all entities not deemed necessary for preservation. In the end, Manlevelt even maintains that substance does not...