Master Nicholas of Amsterdam was a prominent master of arts in Germany during the first half of the fifteenth century. He composed various commentaries on Aristotle's works. One of these commentaries is on the 'logica vetus', the old logic, viz. on Porphyry's 'Isagoge' and on Aristotle's 'Categories' and 'On Interpretation'. This commentary is edited and introduced here. Nicholas is a 'modernus' - as opposed to the 'antiqui', who were realists - which means that he is a conceptualist belonging to the university tradition that accepted John Buridan (ca. 1300-1360 or 1361) and Marsilius of Inghen (ca. 1340-1396) as its masters. In medieval philosophy, a parallel between thinking and reality is generally upheld. Nicholas makes a sharp distinction between the two; this may be interpreted as a step towards a separation between the two realms, as is common in philosophy in later centuries. Other characteristics of Nicholas are that he defends the position that science has its place in a proposition, and does not simply follow reality. Furthermore, he emphasizes the part played by individual things. 0Fifteenth-century philosophy has hardly been studied, mainly because that century has long been considered unoriginal. Nicholas of Amsterdam certainly deserves the historian's interest in order to evaluate how medieval philosophy prepared the way for modern philosophy.