At the beginning of Hesiod's Theogony, there are two odd verses (
v. 54-55):
Μνημοσύνη, γουνοῖσιν Ἐλευθῆρος μεδέουσα,
λησμοσύνην τε κακῶν ἄμπαυμά τε μερμηράων
Mnemosyne (Memory), who reigns over the hills of Eleuther, gave birth
to a forgetting of ills and a rest from sorrow
The Nine Muses are daughters of Memory and the gift of Memory is Forgetting (through the Arts).
Nice pun on Μνημοσύνη ( = ἀλήθεια) and λησμοσύνη (= λήθη). The Greeks identify Memory (ἀνάμνησις) and Disclosure of Truth (ἀλήθεια) but here Hesiod also says that Oblivion is the godly gift by Memory, instead of its negation.
The Muses have just defined themselves by the verses:
ἴδμεν ψεύδεα πολλὰ λέγειν ἐτύμοισιν ὁμοῖα,
ἴδμεν δ᾽, εὖτ᾽ ἐθέλωμεν, ἀληθέα γηρύσασθαι.
we know how to speak many false things as though they were genuine;
but we know, when we will, to utter Truths
The Muses are Memory and Oblivion because they are beyond Truth and Falsity through poetry.