Full Idea
The reality of the past (a 'heavyweight implication') ...is something we know to be implied by things we remember, but it is not itself something we remember.
Gist of Idea
We know past events by memory, but we don't know the past is real (an implication) by memory
Source
Fred Dretske (The Case against Closure (and reply) [2005], p.35)
Book Reference
'Contemporary Debates in Epistemology (2nd ed)', ed/tr. Steup/Turri/Sosa [Wiley Blackwell 2014], p.35
A Reaction
If I begin to doubt that the past is real, then I must necessarily begin to doubt my ordinary memories. This seems to be the modus tollens of knowledge closure. Doesn't that imply that the modus ponens was valid, and closure is correct?