As a Titan daughter of Ouranos (Heaven), Mnemosyne was also a goddess of time. She represented the rote memorisation required, before the introduction of writing, to preserve the stories of history and sagas of myth.
In this role she was represented as the mother of the Mousai (Muses), originally patron goddesses of the poets of the oral tradition.
Finally Mnemosyne was a minor oracular goddess like her sister-Titanes. She presided over the underground oracle of Trophonios in Boiotia.
The Titanis Mnemosyne was sometimes described as one of three Elder Titan Mousai (Muses), who preceded the nine daughters of Zeus as goddesses of music.
Elder Titan Mousai
THE MOUSAI TITANIDES were three or four elder Muses, the Titan goddesses of music. They were named Melete (Practise), Aiode (Song), and Mneme (Memory). The last of these was surely identified with the Titanis Mnemosyne (also Memory), mother of the nine celebrated Olympian Muses by Zeus.
The two sets of Muses, however, were really just alternate versions of the same set of goddesses. A third group were the Muses Apollonides.