[1] Michael Quinion, a British etymologist, writing on his website on linguistics, says, "It is thought that the expression was originally to set on cinque and sice (from the French numerals for five and six).
In 1484, the Lord Mayor of London Sir Robert Billesden decided that the companies would swap between sixth and seventh place on an annual basis.
This story is disproved as a source, according to Quinion, by the "brute force of the evidence" that the phrase was in use and that it occurred in Chaucer a century before the trade guild dispute was decided.
Pinafore (1878), where Captain Corcoran, the ship's Commander, is confused as to what choices to make in his life, and exclaims in the opening song of Act II, "Fair moon, to thee I sing, bright regent of the heavens, say, why is everything either at sixes or at sevens?"
In chapter three of the 1926 Clouds of Witness by Dorothy L. Sayers the maid, Ellen, says, "Anyhow, it was all at sixes and sevens for a day or two, and then her ladyship shuts herself up in her room and won't let me go into her wardrobe.
"[4] The phrase occurs in Sabina's opening monologue from Thornton Wilder's 1942 Pulitzer Prize winning play The Skin of Our Teeth: "The whole world's at sixes and sevens, and why the house hasn't fallen down about our ears long ago is a miracle to me."