In one of his many stories of Lincoln, his law partner, W. H. Herndon,
told this as illustrating Lincoln’s shrewdness as a lawyer:
“I was with Lincoln once and listened to an oral argument by him in
which he rehearsed an extended history of the law. It was a carefully
prepared and masterly discourse, but, as I thought, entirely useless.
After he was through and we were walking home, I asked him why he went
so far back in the history of the law. I presumed the court knew enough
history.
“‘That’s where you’re mistaken,’ was his instant rejoinder. ‘I dared
not just the case on the presumption that the court knows everything--in
fact I argued it on the presumption that the court didn’t know
anything,’ a statement, which, when one reviews the decision of our
appellate courts, is not so extravagant as one would at first suppose.”