The Introduction to philosophy written by Porphyry at the end of the second century AD is the most successful work of its kind ever to have been published. Porphyry's aim was modest, but he gave highly influential treatments of a number of perennial philosophical questions. Jonathan Barnes presents a complete new English translation, preceded by a substantial introduction and followed by an invaluable commentary, the first to be published in English and the fullest for a century, whose primary aim is to analyze and assess the philosophical theses and arguments which the Introduction puts forward.