I ought to be working but I have to amplify on Den Beste's latest on form vs. substance.
Human memory is notoriously unreliable. Unbelievable memories can be made up out of whole cloth. (False memory, memory, and repressed memory therapy from the Skeptic's Dictionary.) It is also extremely difficult to project a lack of knowledge back in time, as I discussed in my Learning to Expect the Unexpected post.
One of the differences between "form" and "substance" is that to the extent that form lives in our human minds, it is much easier to change than substance is. Changing the substance of history... well, that is objectively impossible. Changing the current perceptions, ah, thanks to the nature of the human brain, now that is easier.
