Do You Still Know After Forgetting the Original Reason?

You know that Canberra is the capital of Australia, yet you can no longer recall the book or teacher from which you learnt it years ago. Have you lost the knowledge, or only the ability to state your reason on demand? Epistemologists call this the problem of forgotten evidence: we often retain a judgement after losing access to the evidence that first supported it.

Internalist views that require justification to remain mentally accessible face a difficulty here, because much ordinary knowledge persists in memory in exactly this way. Externalist or reliabilist approaches instead emphasise that a belief may retain its epistemic standing if it was originally well grounded and was then preserved by a normally functioning memory process. Memory primarily preserves the justification; it does not create a new one.

Forgetting cannot, however, cleanse every belief. If the judgement began as ungrounded gossip, forgetting the source does not turn it into knowledge. If strong counterevidence later appears, continuing to rely on the old memory may also cease to be justified.

My view is that losing the original reason does not usually destroy knowledge at once, but it can reduce our entitlement to insist on it in disputed or high-stakes settings. Ordinary knowledge may rely on reliable preservation. Once challenged, we should recover evidence rather than treat “I have always remembered it that way” as a final proof.

https://plato.stanford.edu/entries/memory-episprob/
https://iep.utm.edu/epis-mem/