Quotes Uncovered: Spelling, Logic, and Frenchmen

Twelve weeks ago, I invited readers to submit quotations for which they wanted me to try to trace the origins, using The Yale Book of Quotations and more recent research by me. Hundreds of people have responded via comments or e-mails. I am responding as best I can, a few per week.
Ben asked:

I have always wanted to verify one of my favorite quotes, attributed to Samuel Johnson (author of the first English dictionary): “It is indeed a dull man who can think of but one way to spell a word.”

The Yale Book of Quotations notes that this is frequently attributed to Mark Twain, but the earliest occurrence found in research for the YBQ was in Marshall Brown‘s “Wit and Humor” (1880): “A man must be a great fool who can’t spell a word more than one way.”
Steve Schwartz, a New York City LSAT tutor, asked:

Would love to find the source for: “Man always has two reasons for the things he does: the logical one and the real one.” Thank you!

The YBQ lists this under J.P. Morgan:

“A man always has two reasons for what he does: a good one, and the real one.” Quoted in Owen Wister, Roosevelt: The Story of a Friendship (1930).

Jonathan asked:

“Impossible n’est pas Français.” [“Impossible is not French.”] I’ve often, but not always, seen it attributed to Napoleon Bonaparte. Just wanted to know if it was true.

The Yale Book of Quotations cites Napoleon’s July 9, 1813 letter to Lemarois:

Ce n’est pas possible … cela n’est pas Français.

The YBQ then notes that this is usually quoted as “Impossible? The word is not French.”