Full Idea
Either you perceive the being of matter immediately, or mediately; if immediately, pray inform me by which of the senses you perceive it; if mediately, let me know by what reasonings it is inferred from those things which you perceive immediately.
Clarification
'Mediately' means 'via some other process'
Gist of Idea
If existence is perceived directly, by which sense; if indirectly, how is it inferred from direct perception?
Source
George Berkeley (Three Dialogues of Hylas and Philonous [1713], II p.208)
Book Reference
Berkeley,George: 'The Principles of Human Knowledge etc.', ed/tr. Warnock,G.J. [Fontana 1962], p.208
A Reaction
A problem for strong empiricists, and he is right that existence can't be directly perceived, but it seems a good explanation (for which some reason can be shown), and supports a more rationalist view.