Arcanist Archetype, Unlettered Arcanist

oldraven

The Unlettered Arcanist has a few problems. 

This character gains spells from the Witch spell list instead of the Wizard/Sorcerer spell list, and stores those spells in a familiar in place of a spell book. 

HOWEVER, the archetype does not gain an Outsider patron as a Witch does. The Outsider is the source of the Witch's spells so they do not have spell books. Does the Unlettered Arcanist have the ability to learn spells from a Wizard/Sorcerer spell book? Or do they need to find a Witch to teach them new spells?

This seems a significant omission. 

sindenky

Familiar

An unlettered arcanist does not keep a spellbook. Instead, she gains a familiar in which she stores her spells as a witch does, though she does not gain a witch’s patron. Treat her arcanist level as her witch level for determining the abilities and benefits granted by the familiar. Anything that would allow an unlettered arcanist to add spells to her spellbook allows her to add spells to her familiar instead.

This ability replaces spellbooks.

As per the bolded text I would assume their Familiar is mechanically the same as a spellbook when adding new spells.

oldraven

The Familiar takes the place of the spell book in regards to storing spells. Not as a source of finding new spells. 

For a Witch character the source of those spells is an Outsider Patron. 

The Unlettered Arcanist does not get that source, and no other source is described. 

As Witches clearly do not keep spell books, and the Archetype is described as pulling spells from the Witch list, this question remains open.