[T]he structure of the dialectic, both between Berkeley and his real-world opponents and between his fictitious characters Hylas and Philonous, is a debate about whether ‘the vulgar’ or ‘the mob’ or ‘the illiterate bulk’ have knowledge of familiar objects like apples, tables, and cherry trees, and if so how. Berkeley’s complaint against his opponents is that, on their theories, it cannot be proved that the gardener knows his cherry tree. He claims that his own theory does not have this defect: the philosopher who has grasped Berkeley’s arguments thereby comes to know that the gardener knows that his cherry tree exists.
Berkeley’s problem with representative realism – we don’t know if we know. From Kennypearce.net