The Importance Of Primary References

I've mentioned it before, but one of the premier Civil War blogs, captained by a high school history teacher named Kevin Levin, is Civil War Memory. I especially enjoy this blog because a primary focus of it's content is how we think and learn about the Civil War (as the blog title makes quite evident).
There has recently been a fascinating storyline unfolding about slaves in the Confederate army that I encourage you to read up on.
In the fourth paragraph of the post, Mr. Levin makes a most salient and important point about how we must utilize primary resources and avoid postwar resources as much as possible in doing good historical research. This is an issue I've been obliquely touching on in my Lost Cause posts, which I promise I will get back to this week, and is a cornerstone of accurate historiography.
Anyway, I posted a comment to his post, and thought I'd share it here...

Hi Kevin,
Great post! You make a point that I want to expand on just a bit, because it is a tremendously important part of good and accurate historical research. You mentioned staying away from post-war sources as much as possible and this is a most salient point. One can never underestimate the effect that retrospection will have on the thoughts, speeches and writings of those involved in a historical moment, thus, as responsible historians we must strive to find the primary sources and the data as close to the moments in question as possible to formulate our conclusions.
Unfortunately, this was not the approach followed by ex-officers, politicians, and historians on both sides in the decades following the war. Just look at Gen Pope's essay on 2nd Manassas in "Battles and Leaders of the Civil War", Jefferson Davis' comments on slavery's role in secession before and after the war, or the multi-volume "Southern Historical Society Papers" These texts are rife with statements collected and recorded after the war and are clearly built around an agenda that was most distinct from that which was present before and during the war. These documents propagated into influential texts by Foote, Freeman, and others, and these inaccurate statements and revised agendas took root. Now, we are left nearly 150 years later not only trying to piece together what really happened, but fixing the extensive damage that these misperceptions wrought.
Now we have a responsibility as historians to be faithful to primary data as we do our research. What we find may be disappointing, painful, surprising, but our own opinions of the findings are not as important as providing a clear and correct interpretation of the data.