Your problem was believing in a misattributed quote. The phrase doesn't appear in Hemingway's works nor letters.There is, on page 174 of "A Moveable Feast" this;"My training was never to drink after dinner nor before I write nor while I was writing." -- Hemingway. Abusive comment hidden. (Show it anyway.)
There is, on page 174 of "A Moveable Feast" this;
"My training was never to drink after dinner nor before I write nor while I was writing." -- Hemingway.