by Jove

• The phrase ‘by Jove’ means ‘by Jupiter’, referring to the Chief Roman God. The Romans would swear an oath in the Law Courts beginning with ‘By Jove…’
• The Roman Playwright Terence (c.185-159 BCE) used the phrase ‘Pro Iuppiter!’ (by Jupiter!) several times in his Plays.

Modern Usage

• ‘By Jove’ was in common useage again by the 16th century CE.
• It was used as an oath to avoid saying ‘I swear by God’, which was considered profane: ‘I swear by Jove that..’
  • Chaucer
    • The OED shows the earliest example was from Chaucer’s Troilus and Cressida, written in c. 1374.
  • John Webster
    • Another example appears in 1575, in a play by John Webster called Apius and Virginia set in the Ancient World.
  • Shakespeare
    • He used the phrase in eight of his Plays.
    • He used it in 1588 with ‘Love’s Labours Lost: ‘By Jove, I always took three threes for nine.’