You're confusing something here.Immanuel Can wrote:Knowledge claims must be based on reasons and evidence, or there's simply no reason to regard them as knowledge claims at all. So making any claim to have knowledge amounts to writing a promissory note to have reasons and evidence for that claim.
That is a voluntary taking on of the "burden of proof."
What's at issue isn't whether someone has reasons and evidence for a claim. When someone makes a(n apparent) claim and doesn't go into detail about reasons/evidence, they may or may not have reasons and evidence that they consider to support it. The mere fact that they didn't express or go into any detail about their reasons or evidence that they consider to support a claim doesn't imply that they do not have any reasons or evidence that they consider to support it.
Burden of proof is about rhetorical or conversational behavior--rhetorical or conversational etiquette. It's something that other people are demanding about behavior--that one present one's reasons or evidence if one has them, because given the context--the nature of the claim in question, the context in which it occurred conversationally, etc., it's "claimed" that one has the burden of proof, and often contra someone else participating in the conversation who is also making claims.