From Greek EISAGOG , introduction, import, initiation, EIS, inside, inward and AGO, drive, drive : enter, carry inside. Book written by the neoplatonic philosopher Porfirio, disciple of Plotino, of the neoplatonic school of Rome in the 3rd century, on Aristotelian categories. This Introduction to Aristotelian Categories was used as a text of Aristotelian logic in European universities throughout the Middle Ages.