Commentary Purg XXVIII 127-132

Having answered both of Dante's questions ([Purg XXVIII 85-87]) Matelda now turns her attention to the twofold river in this garden.  The Bible says there are four rivers in Eden, Phison (Ganges), Gehon (Nile), Tigris, and Euphrates (Genesis 2:10-14).  Dante says there are two, Lethe and Eunoe.  The first of these is looked forward to by Virgil ([Inf XIV 136-138]) in response to Dante's wrongful assumption that it is a river in hell.  The second, Eunoe, appears to be no less than a Dantean invention.  Thus Dante has first of all reduced the number of the garden's rivers from four to two.  Cioffi suggests that he does so in order to avoid having the same numbers of rivers in this good place as there are in hell (four): Acheron, Styx, Phlegethon, Cocytus (see 'Eunoe' in The Dante Encyclopedia [Lans.2000.1], p. 358).  It was probably also Dante's intent to replace the two he does later name (Tigris and Euphrates at [Purg XXXIII 112]) both for practical and symbolic reasons.  It would have been difficult or impossible to argue that the Tigris and Euphrates ran from Eden to Armenia and thence into the Persian Gulf; in any case, and as Singleton (Sing.1958.1), pp. 167-68, has argued, Dante wanted two rivers here that would serve a purpose in 'the process of man's purgation and redemption from sin.'  And so, while indicating that he knows we expect those other four rivers, he gives us these two.  Thus, when he in fact does refer to the 'orthodox' rivers, Tigris and Euphrates, he is winking at the reader who expects to find them here along with two others.  The fact that, when he does mention the 'correct' paradisal rivers, he chooses to refer to only two of them seals his playfulness, for these two rivers, Lethe and Eunoe, look just like them.  For a study of Dante's highly idiosyncratic hydrography, see Donno (Donn.1977.1).

      Lethe is the classical river of oblivion, present in the poets best known to Dante: Virgil (Aen. VI.713-715, where drinking from it deprives the soul of its entire remembered experience and thus prepares it for another life), Ovid (Metam. XI.602-604), Statius (Theb. I.296-298), Lucan (Phars. V.221-222).  As for the word Eunoe, a Dantean Greek-derived coinage, Tommaseo (DDP Tommaseo.Purg.XXXIII.127-129) was perhaps the first commentator to consider Dante as having cited himself (Conv.II.iii.11), when he says that the Empyrean heaven was formed by the divine mind alone, or Protonoe (protos = first; nous = mind).  Here Dante reformulates that Greek term, itself derived by Uguccione da Pisa from Martianus Capella (see Vasoli [Vaso.1988.1], p. 138n.), into eu (good) and nous (mind -- or here perhaps 'memory').