The River of Forgetfulness According to Greek Mythology
Planescape : Torment (PS:T) suggests, that the waters of the river Styx causes one to loose ones memories if one drinks from them. But is that true? Did the waters of Styx cause forgetfulness according to greek mythology? The answer is no. The waters of Styx did not cause forgetfulness according to greek mythology.
But if the waters of Styx of not cause forgetfulness what do they do then? Let us turn to Hesiod, who in his work "Theogony" will give us the answer:
 And there dwells the goddess loathed by the deathless gods, terrible Styx, eldest daughter of backflowing Ocean. She lives apart from the gods in her glorious house vaulted over with great rocks and propped up to heaven all round with silver pillars.
 Rarely does the daughter of Thaumas, swift-footed Iris, come to her with a message over the sea's wide back. But when strife and quarrel arise among the deathless gods, and when any one of them who live in the house of Olympus lies, then Zeus sends Iris to bring in a golden jug the great oath of the gods
 from far away, the famous cold water which trickles down from a high and beetling rock. Far under the wide-pathed earth a branch of Oceanus flows through the dark night out of the holy stream, and a tenth part of his water is allotted to her.
 With nine silver-swirling streams he winds about the earth and the sea's wide back, and then falls into the main; but the tenth flows out from a rock, a sore trouble to the gods. For whoever of the deathless gods that hold the peaks of snowy Olympus pours a libation of her water and is forsworn,
 must lie breathless until a full year is completed, and never come near to taste ambrosia and nectar, but lie spiritless and voiceless on a strewn bed: and a heavy trance overshadows him. But when he has spent a long year in his sickness,
 another penance more hard follows after the first. For nine years he is cut off from the eternal gods and never joins their councils or their feasts, nine full years. But in the tenth year he comes again to join the assemblies of the deathless gods who live in the house of Olympus.
 Such an oath, then, did the gods appoint the eternal and primeval water of Styx to be: and it spouts through a rugged place.
(Hesiod, Theogony, section 775-805)
But if it is not the waters of Styx, which cause forgetfulness, which waters are it then? Let us look to Nonnos for the answer in his work "Dionysiaca":
"Lie there, you corpse, in foreign waters; and may your father Hydaspes cover dying Deriades. I will destroy you both, goodfather and goodson, shaking my Euian thyrsus with point wreathed in vine, instead of bloodstained spear and wellsharpened sword. But you killed yourself with gory steel, and so you never drank the luxurious water of the honeyd-distilling river; a river has covered you, but you missed the delicious wine. Drink up the whole river alone, if you like; but you shall have river-water enough when you drink the fatal water of Acheron. Your belly swells already with the bitter water of a murdering stream, and teems quick with Fate; buttaste of Cocytos, and drink Lethe if you like, that you may forget Ares and the bloody steel."
(Nonnos Dionysiaca 17.292-305)
The river of forgetfulness, according to greek mythology, is thus not the river of Styx, but the river of Lethe. But why has this error been made in PS:T? Why is it suggested in PS:T, that the waters of Styx cause forgetfulness when that is incorrect according to Greek mythology? As far as I see it, it is not very likely, that the PS:T team knew the difference between Styx and Lethe in greek mythology. Why should they on purpose implement a lore error in the game? It is therefore more likely, that the lore error stems from the original Planescape rulebooks, which the computergame PS:T was based on. It is an error, however, which has no bearing on the game plot's overall stability. Should an updated version of the game be made sometime in the future the name could easily be changed from Styx to Lethe, thus correcting the problem.