Book IV of the commentary of Proclus (412-485) on the Parmenides of Plato, the longest of all the work is devoted to Parm . 130 E 4-135 B 2, continuation and end of the discussion of ideas between Parmenides and Socrates. After discussing, in Book III, the first and second of four issues listed at the beginning of Book III, namely the existence of ideas and the realm of ideas, Proclus happening here in the discussion of the third and fourth problem, namely the nature of ideas and how they are investees. These two issues are discussed in reverse order: first, the way ideas are investees ( Parm 130 E 4-132 B 2.) then the nature of ideas ( Parm 132 B B 3-135. 2). Six paradoxes raised by Parmenides against the doctrine of ideas are interpreted as maieutic questions to be traced from Socrates body to intangible forms and transcendent passing through all intermediate degrees. The first two paradoxes come the problem of participation, the last four, the problem of the nature of ideas. Examination of six paradoxes by Proclus is one of the most complex and most important treaties that metaphysics of Late Antiquity has provided. This volume follows the first three volumes appeared, too, in the Collection of the Universities of France (vol. I: 2007, vol II. 2010 Vol III., 2011). It contains an introduction, critical edition of the text, the French translation and a rich commentary that addresses all the issues raised by the text, both philological and philosophical. It will be supplemented by a series of four indexes: (1) Index Nominum, (2) Index locorum (3) Index rerum notabilium (4) Index of passages discussed in the notes.