Larry McMurtry, in his NYRB review of Grant and Twain: The Story of a Friendship That Changed America, by Mark Perry, quotes Grant’s famous description of meeting the defeated Lee at Appomatox, one paragraph of which reads:
What General Lee’s feelings were I do not know. As he was a man of much dignity, with an impassible face, it was impossible to say whether he felt inwardly glad that the end had finally come, or felt sad over the result, and was too manly to show it. Whatever his feelings, they were entirely concealed from my observation; but my own feelings, which had been quite jubilant on the receipt of his letter, were sad and depressed. I felt like anything rather than rejoicing at the downfall of a foe who had fought so long and valiantly….
(I urge you to read the rest of the quote at the linked article; Grant was a wonderfully vivid writer.) McMurtry then remarks on one word in the passage:
Spelling, in the nineteenth century, was, in the main, a field for creativity; Grant spelled as the spirit moved him. In the passage quoted, from the Library of America edition, there is one word that bears looking at: “impassible,” referring to Robert E. Lee’s face. Jean Edward Smith, in his excellent biography of Grant, corrects this to “impassive,” which is no doubt what was meant; but the word suggests at least a few of the seven types of ambiguity the critic William Empson used to brood over. Was Grant merely saying that Lee had such perfect control over his emotions that no shadow of what he might be feeling could pass across his features? But might the word also have a military shading? The fact, or at least the legend, of Lee’s “impassibility” was a big problem for the Union generals, until Grant came along and started winning battles.
However, Merriam-Webster gives ‘impassive’ as a second meaning of impassible, so I’m not sure why Smith would feel the need to emend it. In any event, I always enjoy such ruminations over the implications of a word.
Addendum. While I’m on the subject of Grant, I should quote the last of the notes he passed to his doctors as he was dying of throat cancer:
I do not sleep though I sometimes doze off a little. If I am up I am talked to and in my efforts to answer cause pain. The fact is I think I am a verb instead of a personal pronoun. A verb is anything that signifies to be; to do; to suffer. I signify all three.