A Franciscan friar who collaborated with Leonardo da Vinci codified modern accounting.
In 1494, Luca Pacioli, a Franciscan friar and mathematician, published Summa de arithmetica, geometria, proportioni et proportionalità in Venice.1 The book was a comprehensive mathematics textbook, but a single section on bookkeeping alla veneziana, the Venetian method, would outlast everything else in it. Pacioli described a system in which every financial transaction was recorded twice, as both a debit and a credit, so that the books always balanced.2
Pacioli did not invent the system. Venetian merchants had been using double-entry methods for at least a century before he wrote about them. The earliest surviving examples of double-entry records date to the commune of Genoa around 1327, and Florentine merchants used a version by the 1380s.3 What Pacioli did was codify the practice in print, making it teachable and exportable.
He was a collaborator and friend of Leonardo da Vinci. Leonardo drew the illustrations for Pacioli's later book De Divina Proportione, published in 1509.4
Written in Italian rather than Latin, the Summa was accessible to merchants and tradespeople. The section on bookkeeping became an accounting textbook used across Europe through the mid-sixteenth century.5 Jan Ympyn Christoffels published the first adaptation in Antwerp in 1543, and James Peele wrote the first English-language accounting text in 1553.6
The essentials of the system Pacioli described, debits on the left, credits on the right, every transaction entered twice, have remained largely unchanged for over five centuries. In early modern Europe, the system carried theological overtones, recalling the scales of justice and the symmetry of divine order.7