Full Idea
If the mental image of a train timetable cannot itself be tested for correctness, how can it confirm the correctness of the first memory? (As if someone were to buy several copies of the morning paper to assure himself that what it said was true).
Gist of Idea
We cannot doublecheck mental images for correctness (or confirm news with many copies of the paper)
Source
Ludwig Wittgenstein (Philosophical Investigations [1952], §265)
Book Reference
Wittgenstein,Ludwig: 'Philosophical Investigations', ed/tr. Anscombe,E. [Blackwell 1972], p.94
A Reaction
An important point for the epistemological sceptic. Could God do an infinite regress of checks on the truth of his mental images?