〜すら / 〜でさえ (even — register distinction)
〜すら / 〜でさえ Formality Level: すら = Literary/Formal; でさえ = Semi-formal; さえ = Neutral; でも = Casual Classical Origin: すら is one of the oldest particles in Japanese, appearing in the Man'yoshu (8th century) and Kokinwakashu (905 CE). In classical Japanese, すら marked "even X (the minimum or most unexpected element on a scale)." The Heian poet Fujiwara no Teika used it to mark extreme emotional states: "even the spring...